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TITLE: HIGH INTENSITY SRF PROTON LINAC WORKSHOP (VUGRAPHS) S° £*§!* 2 5 ItfS § •s^2,§ I?

AUTHOR(S): •-(3D CD « Brian A. Rusnak and AOT-1 o g CD a II Several external authors So --I; !-' i J*> a . c ca a g E a a o..2 (500 double-sided a 4> ,0 u £ 00 O •" « 6*3 o g • vugraphs) TS S 2 c _. ,1 o. «> ""S8SI Is M E t S II 'S « O O Si * 5- II "S2 O« g B.to & S - p l'i is 8 » s* « '3 o s ii 1? SUBMITTED TO: High Intensity SRP Proton Linac Workshop. •?« I Santa Fe, NM •It! •5 -c May 7-10,1995 o o li §2 n J3

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NATIONAL LABORATORY

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Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. Proceedings for the High-Intensity SRF Proton Linac Workshop

May 7-10, 1995 Hotel Santa Fe Santa Fe, NM General Introduction

Opening Remarks P. Lisowski Page APT Accelerator Overview G. Lawrence Page

Operating Experience Talks

TRISTAN SRF System S. Noguchi Page CEBAF: status, outlook, C. Leemann Page and lessons learned H. Klein Page ESS Linac Design D. Chan Page APT Superconducting RF Linac High Current High Gradient Superconducting Cavities H. Padamsee Page Cavitv-Structures Working Group

Summary Report T. Wangler, J. Delayen (Chairmen) Page Summary Viewgraphs J. Delayen Page

Presented Viewgraphs Linac Architecture T. Wangler, E. Gray Page Cavity Design F. Krawczyk Page Structural Considerations R. Genzlinger Page CEBAF Experience A. Hutton Page Beam Physics C. Bohn Page Cryostat Candidate Design R. Gentzlinger Page R&D Program and Discussion T. Wangler Page Couplers and rf Working Group

Summary Report P. Tallerico, H. Padamsee (Chairman) Page Summary Viewgraphs H. Padamsee Page

Presented Viewgraphs rf Architectures D. Rees Page Coupler Comparison H. Padamsee Page Window Assessment H. Padamsee Page Power for HPP H. Padamsee Page HOM Coupler H. Padamsee Page R&D Recommendations H. Padamsee Page Upgrade Paths J. Delayen Page System Integration Working Group

Summary report T. Moore, Chairmen Page Summary Viewgraphs K. Bongardt Contributed Viewgraphs RT linac For Protons J-M. Lagniel Page Design Of A Superconducting H. Heinrichs Page H-Linac for ESS GENERAL INTRODUCTION Opening Remarks

Presentation to the High-Intensity SRF Proton Linac Workshop May 7-10, 1995 Paul Lisowski Los Alamos National Laboratory APT Project Leader APT Major Subsystem Features

Accelerator Target/Blanket • Produces and • Produces neutrons accelerates from proton beam proton beam • Converts 3He (or 6Li) into tritium

High-Energy Tritium Beam Transport Processing • Proton beam delivery • Continuous tritium to Target/Blanket extraction • Expands and shapes • Purification to weapons beam grade tritium APT Design Objectives

Meet tritium production requirements with adequate margins

Use existing technology wherever possible

Simplicity

High reliability

Safety by Design

Waste minimization APT Design Parameters Over Time

1989 1990 1991 1992 1993 1994 1995

1600 MeV 800 MeV 1000 MeV 1000 MeV 250 mA 150mA 200 mA 100mA Full Goal 1/4 Goal 3/8 Goal 3/16 Goal

JsBk A ERAB 1992 JASON 1995 JASON Review Review Review Expectations from Project Office

• Update on status of SCRF technology worldwide

• Get concensus opinion from SCRF community - Technology maturity - Applicability to APT

*

• Identify areas needing further work - Identify where that work can be done - Determine how to proceed APT Accelerator Overview

George Lawrence Los Alamos National Laboratory

Workshop on High-Intensity SRF Proton Linac Design

Sfttita Fe, NM 8-10, 1995 Evolution of APT Linac Design Raa*awigaaMaanMM(iMiMHiMaaBWM^^

•• 1992 Basic linac concept reviewed by JASONs - conservative design philosophy _. — design choices within present technology base, or moderate extensions • 1992-3 DOE-funded design study - 200-MW beam power requirement; production by 2008 • - 1000-MeV, 100-mA tunneled RT linac - preconceptual design report - detailed cost estimate • 1994 Power requirement reduced to 100 MW, with upgrade potential to 200 MW - non-funnelad 1000-MeV, 100-mA RT linac - upgrade to 200 mA by adding LE linac, funnel, RF power

/ LANL High-Power Linac Concept 1000-MeV, 200-mA CW Funneled System

Funnel 350^. Coupled Cavity Linac (CCL) (700 MHz, 200 mA) .

BCDTL 14-Cell Tanks (700 MHz) 100 MeV Doublet Focusing 1000 MeV 20MeV 7.0 MeV Matching & Halo Scraping 75keV

30 m 110m- 1040 m-

Beam power 200 MW Total RF power to %i*K> 264MW RF to beam'tffkttwitey 0J87 AC to RF efflQJfcrtoy \ 0,582 RF trans^ort^tf^l^ricy 0-950 AC to beam effifefeticy 0.435 AC power faqutferftertt 405 MW CCL structMne^r&$#r»t 1,3-1.5MV/jn

Transverse, .9$$!$ £jnjjttance 0,04 n cmTii)ravd CCL apm^M^m^m ratio 13-26 1000-MeV, 700-MHz Coupled-Cavity-Linac for APT

Side-couplea n/2-mode structure similar to LAMPF 1000 MeV module Short tanks (14 cells) allow strong focusing • Structure power: 130 kW CW cooling for 1.4 MV/m • RF efficiency: •• 0.83 structure gradient • Energy gain: 3.0 MeV

wr.ir—*•

Los Alamos APT Output Beam Distribution From End-TorEnd Linac Simulation Ideal Linac —1000 MeV, 10,000 Macropartirles

.005 .005 xp vs. x

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10.0

] Beam loss in LAMPF CCL estimated from activation (3 months operation at 1 mA)

w Relative beam loss predicted by simulation w o (normalized at 100 MeV) "8 E W 111

R°rrn-i-iQ|U°i 300 400 500 600 700 800 Proton Energy (MeV) LAMPF APT Design Beam loss in much of CCL is very low Losses must be < 10-8/m at 1000 MeV. (<2x10-7/m). Strong focusing provides very large Activation levels are a few mR/hr. aperture ratio (13-26 in CCL). Most loss is from RF/beam mismatch Large acceptance transitions avoided, in turn-on transients. above 20 MeV. High losses from longitudinal and Precise matching between adjacent . transverse acceptance transitions. accelerating structures. Moderate aperture ratio (4-6.3). Halo scraping at 20 MeV. Evolution of APT Linac Design

1994-5 New RT linac design, based on - CCDTL .to replace low-p, transition-p structures - improved focusing lattice (short-period FODO) - RF modularization scheme for increased availability 19.95 Reviews by LLNL, JASONs - agree presented baseline design would do the job - endorse move to new RT concept (CCDTL, FODO lattice) - suggest assessment of SRF technology for HE linac 1995 Recent discussions with "customers" suggest - beam power requirement will be about 130 MW - desired initial production date is late FY2005 700-MHz CCDTL as Basis for Improved Linac Design

iy*-mounted TMoi* coopSog ceB Low. energy - 2 drift-tubes per cell - 5pA/2, 3pA/2 - Could follow R.FQ - Increases, fuonefeg energy options.

Quadrupole lens Two-

Longer coupling celt Intermediate energy - 1 drift-tube per cell - 3pX, 1 $\ - Replaces BCDTL

Short coupling ceR

Sideways-mounted coupling cefl Conventional coupling cefl spanning the pX/2 bead spsce between cavities High energy - Conventional SCL - 7 cells per tank -.- 7 pA/2, 1 pA/2 - Cell can be omitted for diagnostics.

Los Alamos Baseline Conventional Linac for 3/16-Goal

Potential Beam Transport Injector Funnel Point I 350 MHz 700 MHz / 700 MHz 700 MHz m WWP Targets 100 mA | 100mA 100 mA 75 keV 7 MeV 12MeV 100 MeV 1000 MeV

100MW ppwer J355\!V!W %£:££& ^ 130 rfi - ! *$<

APT Advanced Linac Concept for 3/16-Goal

Beam Transport Injector 350 MHz 700 MHz

APT Principal Issues for High Power Linacs

• Cost - construction post (RF power dominates) - life-cycle cost (NPV) • Power conversion - AC-RF efficiency * -' RF-beam efficiency • pperability - beam (oss control; halo suppression - function of key components at high power levels - RF generator/cavity/beam control - turn-on, fault handling, system protection • Availability - component lifetime; failure diagnostics - replacement/service time intervals - component redundancy Neutron Production Efficiency vs Proton Energy (cylindrical Tungsten target 50-cm diam x 100-cm-long)

100

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Waveguide AC-DC Conversion Losses Losses 8MW 5MW

, **:*::i::':iiU:::::i:i!iSiii::ji':'!'' Present Baseline RT Linac Design for Comparison with SRF Point Design

100-MW non-funneled linac (1000 MeV, 100 mA) 7-MeV, 350-MHz RFQ 100-MeV, 700-MHz CCDTL 1000-MeV, 700-MHz GCL FODO focusing lattice in CCDTL, CCL (8pX) Aperture factor > 13 - 26 (100 MeV -1000 MeV) Linac is divided into modules, each driven by seven 1-MW klystrons; can tolerate single tube failure Objectives of the High-Power SRF Linac Workshop

• Critique a strawman SRF linac point design. • Determine the main technical issues for an SRF -V high-power proton linac. • Assess the state of SRF technology and its relevance to high-power proton linacs. • Outline a technology development program that would provide the confidence to build APT linac as an SRF system. • Assemble preliminary cost information that will allow a comparison of SRF and RT point designs. OPERATING EXPERIENCE TALKS

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£\ V^^p, Le-tck Kt &€*.* Pipe r CEBAF: STATUS, OUTLOOK, AND— ^ LESSONS LEARNED

Christoph W. Leemann

^CEBAF !—:—• The Continuous Electron Beam Accelerator Facility lls [cwltalks]Santa Fe wrkshp, 5/8-10/95 8 May 1995 ^ AT A GLANCE

CEBAF is: • A nuclear physics laoratory with a strong program and a bright future • A $600 M project on cost and schedule • World's largest srf (superconducting rf) and 2 K cryogenics installation • A resource in advanced accelerator science and technology

It is a success because we: • Anticipated expanding user needs • Analyzed and accepted the risk of forefront technology • Managed the project soundly

0SE8AF* ~~ The Continuous Electron Beam Accelerator Facility ' lls [cwltalksJSanta Fe wrkshp. 5/8-10/95 8 May 1995 SITE PLAN iTD.A

BEAM SWITCHYARD s:t=PL3Cjm 4/11/92 — Boundaries of DOE Owned or Leased Property 0 500"

Boundaries of SURA Property p-i OVERVIEW

• Electrons for strong interaction physics: the CEBAF program and its

accelerator requirements

• The CEBAF accelerator: from concept to upgrade plans

• Why srf is so great: spin-offs and applications

• $600 M on cost and schedule: lessons learned from a high-tech project

The Continuous " ~ tron Beam Accelerator Facility lls [cwltalks]Santa Fe wrkshp, 5/8-10/95 8 May 1995 ELECTRONS FOR STRONG INTERACTION PHYSICS FIRST ROUND OF PHYSICS EXPERIMENTS

Totals of Approved Experiments

Topic Hall A HallB Hall C Total Nucleon and Meson Form Factors; Sum Rules 3 3 4 10 Few Body Nuclear Properties 7 . 4 3 14 Properties of Nuclei 4 8 3 15 N* and Meson Properties 3 20 2 25 Strange Quarks 2 7 3 12 TOTAL 19 42 15 76

542 users from 114 institutions in 20 countries are collaborators on approved experiments User Group currently has about 960 members

A The Continuous Electron Beam Accelerator Facility lis [Leemann/talks] APS mtg/4/95 18 April 1995 SIMULTANEOUS COMPLEMENTARY EXPERIMENTS VUGRAPH

lis [cwltalks]Santa Fe wrkshp, 5/8-10/95 8 May 1995 The Continuous Electron Beam Accelerator Facility r MAJOR ACCOMPLISHMENTS IN HALL CONSTRUCTION

• Hall C • High momentum spectrometer (HMS) achieved its design specification • Short orbit spectrometer (SOS) complete in March • First physics experiment in Hall C scheduled in April • Hall A ; • First superconducting dipoles for high resolution spectrometers (HRS) assembled and will be mapped in March • Assembly of the rotating carriage systems well underway • Three of the large superconducting quadrupoles successfully tested at the manufacturer • HallB • Assembly of the large superconducting magnetic toroid completed with cool down and full field testing planned for late February (CEBAF large acceptance spectrometer (CLAS) • Three of the largest drift chambers successfully strung and construction of other detector items is well advanced

^feggJkP ' The Continuous Electron Beam Accelerator Facility ' lls NltalksJSanta Fe wrkshp, 5/8-10/95 8 May 1995 THE ACCELERATOR REQUIREMENTS:- YESTERDAY, TODAY, AND TOMORROW

Yesterday Today Tomorrow

Energy [GeV] 4 to 6 8 to 10, possibly more

Polarization [%] None 40 in 1 hall; 80 in 3 halls working towards

80 in 3 halls

Current IMA] At least 200 100 to 200 100 will do Duty factor [%] 100 100 >50 Ap/p [10i <1 ~1 A few

I lis [Leemann/talks] APS mtg/4/95 18 April 1995 The Continuous Electron Beam Accelerator Facility THE CEBAF ACCELERATOR

»• THE CHALLENGES AND THE SOLUTIONS OF THE cw ELECTRON ACCELERATOR

• Control the power cost: srf

• Control capital; expense: beam recirculation

• Leave room for energy upgrade: arcs design

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^T . " ?r , r, A ,MfBHC„««„ * lis [cwltalks]SantaFewrkshp, 5/8-10/95 8 May 1995 The Continuous Electron Beam Accelerator Facility l J /-CHALLENGES: POWER

• For a 4 GeV normal conducting linac, neglecting beam loading: P = ?]rf1EG/(r/Q).Q-1 r/ = rf conversion efficiency [<- 50%] rf G[MV/m] L[m] P[MW] E = beam energy [~ 4 GeV] 1 4000 160 G = accelerating field 2 2000 320 r/Q = shunt impedance/unit length (r/Q)-Q = 5 • 107 QJm] 3 1333 480 Q = quality factor

• For a 4 GeV superconducting linac:

1 P = ?7^0EG/(r/Q).Q- ?7 = cryogenic efficiency [~ 10-3] cryo G[MV/m] L[m] P[MW] {r/Q) -1000 Q/m 5 800 10 9 Q =2-10 10 400 20

The Continuous Electron Beam Accelerator Facility ' lls [Leemann/talks] APS mtg/4/95 18 April 1995 RECIRCULATEDLTNAC CONCEPT •'CEBAFf r BIG ARCS MAKE UPGRADES POSSIBLE

Avoid degradation due to quantum excitation: low fields, large radii, strong focusing; for % bend with radius p over length L + Tcp, .

5 Ae s 1.32* x 1(T27m2 - rad-^r- {tt)

oi s 1.182 x 10"33 GeV2m2 %? P

where (H) = I -JJ bends ds< Tf + \prf-U'Ti

Site limit: s 30 GeV with present tunnel

.^~^^L The Continuous Electron Beam Accelerator Facility lis [cwltalks]Santa Fe wrkshp, 5/8-10/95 8 May 1995 MACHINE CONFIGURATION , MX?

45 ~McV Injector (2 114 Cryomodules)

End. <& Stations M«xi«gC«»«|«> 1/1&-04 r SUMMARY ACCELERATOR DESCRIPTION

Beam performance objectives: • > 4 GeV, 200 JIA, cw • Emittanpe and energy spread: e ~ 2 • 10"9 m, a /E ~ 2.5 • 10'5 • 3 simultaneous beams, independent energy and current adjustment Design concept: recirculating, superconducting cw linac • cw for high beam quality • rf superconductivity for efficiency • 5 pass beam recirculation for cost optimization, multi-energy operation Key design features: • 1 rf system per cavity for control of microphonics and operational flexibility • 2 K operation for cost optimization • Isochronous, achromatic beam recirculation arcs • Strong focusing optics to minimize synchrotron radiation effects

^."1 The Continuous Electron Beam Accelerator Facility lals[leemann/talks]SRF Tech & Ace's March 16,19952 SIMULTANEOUS BEAM DELIVERY CEDAF

Experimental Halls Linac

0 ®o®#o®

Observation at A-A Completed turn Energy 1 • © o • © o • © o 1/5 2 © o • © o • © o 2/5 3 o • o • O 3/5 4 > • • 4/5 5 > • • Full Observation in Experimental Halls Hall A © © <•) Hall B • •% • • Hall C o o o

liiniiillniinoilsUonml JolivoiyMrr.nllJwij n.ln SYSTEM OVERVIEW

• srf Accelerator System • 338 cavities in 42 1/4 crymodules • rf System 340 klystrons in 43 HPAs 344 low level control modules Master oscillator and distribution 3 beam injector rf separators, HPAs, controls Cryogenic System 4800 W, 2 K CHL ESR (end station refrigerator) Transfer lines CHL operational at 2.1 K, -5000 W

V. ,^„EL Tho Continuous Electron Beam Accelerator Facility lis [Loomann/lnlks] APS mlgM/05 l()A[)(il 1005 /-SYSTEM OVERVIEW (conf d.) • i&c • 100,000 i/o point control system operational . • Successfully migrated to EPICS • Supporting operation; improvements ongoing • Beam Transport • 2241 magnets and stands • 4.5 km of vacuum line • Beam clumps, LCW system • Magnet measurement system • Survey and alignment • DC Power • 1831 trim supplies (10"4) • 21 dipole supplies (10-5) • 11 septum power supplies (10"5) . • 84 shunts (10*4)

^-OEBAF = • • : 77)e Continuous Electron Beam Accelerator Facility ,ls [Leemann/lalks] APS mtgM/95 1 o April 1995 r CEBAF COMMISSIONING A MULTI-YEAR PROGRAM • Primary goal: • Preparation for safe and efficient accelerator operation by the time the experimental physics program is ready for beam. • Secondary goals: • Verify (and Correct as necessary) performance of accelerator subsystems • Develop procedures for setup and operation of accelerator • Establish and train accelerator operations staff • Accomplished by tightly linking accelerator commissioning with installation - each major accelerator segment or subsystem was tested with beam as soon as this was practical. • A staged commissioning effort like this is necessary because of the considerable complexity of the CEBAF accelerator.

The Continuous Electron Beam Accelerator Facility * W [WhosefolderAalks] name of talk 3 January 1992 /-MAJOR STEPS IN CEBAF COMMISSIONING s

• 1989/1990 - Injector Tests (conducted in shielded area in test lab) • First test of SRF cavities and RF controls with beam • Develop injector elements, test beam diagnostics • Operation to 5 MeV, 540 pA CW n • 1991/1992 - Front End Test • Operation of full 45 MeV injector, to 330 \UK CW • Study BBU yvith single pass recirculation, to 215 |iA CW • Measure beam characteristics d 1992/1993 - North Linac and East Arc Tests • Operation through north linac (cryogenics limited) to 245 MeV • Beam transport and detailed studies through 3/4 of east arc • Delivery of 110 JIA CW to north linac dump • 1994 • Delivery of single pass (600 MeV) pulsed beam to Hall C for spectrometer commissioning • 1995 • Setup three pass recirculation to 2.1 GeV, interleaved with beam delivery (0.75, 1.46, and 2.17 GeV) beam to Hall C . • Setup five pass recirculation to 4 GeV, delivered beam to Hall C

The Continuous Electron Beam Accelerator Facility ' W [Whosefolder/talks] name of talk 3 January 1992 r CEBAF PERFORMANCE MEETS OR EXCEEDS SPECIFICATIONS • Momentum spread (4a) < 10"4 • Emittance smaller than specification - 2 x 10-9 m (4a) at 1 GeV • Bunch length setup yields < 0.5° • Path length around recirculation paths adjustable to < 0.5°.

• M56 around each arc adjustable to < 10 cm • SRF cavities routinely operated with gradients > 5 MeV/m • 2 K refrigerator performance is spectacular • Beam stability is very good without energy and orbit feedbacks operational • RF separation scheme performs as designed

• First beam transport through the entire third pass was accomplished in six hours, from downloaded magnet settings!

^-®JB3JbF :—: The Continuous electron Beam Accelerator Facility W [Whossfolder/lalks] name ol talk 3 January 1992 ^NEAR-TERM PROGRAM THRUSTS v

• Complete installation of the major experimental equipment in Halls A and B and begin carrying out the approved experimental program • Delivery of 4 GeV beam into Hall C was scheduled for Mar^ch • First delivery of polarized beam to Hall C planned for fall 1995 • Hall A start-up in January 1996; data taking planned for late summer • CLAS detector in Hall B complete in September 1996

• Capability for simultaneous delivery of independent energy and intensity * beams to the three halls available by late 1995

• Evolutionary upgrade to 6 GeV beam available by late FY97 • Accomplished as part of routine, ongoing accelerator maintenance/ development efforts • Transparent to reliable delivery of beam to the end stations

The Continuous Electron Beam Accelerator Facility lls [Leemann/talks] APS mtg/4/95 18 April 1995 f LONG-TERM OPPORTUNITIES

• Highest priority over^the next five years is running presently approved experimental program • Evolutionary extension of the upper energy from 4 to 6 GeV

• User-driven workshop recommended an upgrade into the 8 to 10 GeV region; this energy upgrade particularly cost-effective • Add additional cavities

• Upgrade performance of installed cavities

• Upgrade major dipole power supplies • Further evolutionary upgrades in the performance of the linac structures will allow energies up to about 10 GeV

J The Continuous Electron Beam Accelerator Facility ' lls [Leemann/talks] APS mtg/4/95 18 April 1995 Energy Upgrade to 8 Ge¥ J

® Add 10 high gradient cryomodules in empty slots ® Rework low gradient cryomodules >- Hr ® Upgrade all dipole power supplies ® Replace 5 dipole magnets Cryomodules €> Beef up 1/3 of quadrupoles and suppl Installation in normal shutdowns during 2 years

.# Afo interruption of

;,v normal running , 20 Total cost of Cryomodules Machine Upgrade 5 New ~30M$ Cryomodules

•-,••(... (loiiiiii|*(i/cnr^y.ti|i|*r.('ii jm 1/2.5/95 T/ie Continuous Electron Beam Accelerator -Facility f STATUS SUMMARY

• Construction complete

• Cavities exceed G, Q specs significantly; cryo plant performing flawlessly at 2K

• Commissioning and operation start-up on schedule

• Well positioned for:

• Near-term program goals

• Upgrades to meet five and ten year user expectations

• Applications of technology

K^gggftP , _ / The Continuous Electron Beam Accelerator Facility ' Ils [cwltalks]Santa Fe wrkshp. 5/8-10/95 8 May 1995 I

APPLYING CORE COMPETENCIES

*rt r CEBAF TECHNOLOGY DEVELOPMENT AND v TRANSFER • For CEBAF, cooperative development with industry via an Industrial Advisory Board is a natural by-product of constructing a state-of-the-art accelerator • Innovative and exciting technical approaches have been transferred to industry Examples: • Low co^t technique for fabricating microwave waveguides was developed • Developed a remote radiation monitoring device which is now a commercial product • Developed a new ceramic for absorbing microwave power • An improved method for leak detection is under commercialization • Inexpensive flexible liquid light guides developed • City of Newport News developing 150 acre site adjacent to CEBAF for high- tech research and development park; cornerstone building construction to begin April 1995 • LPC (Laser Processing Consortium) formed to promote industry-led FEL ' project

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The Cont, -. Electron Beam Accelerator Facility lis [cwltalks]Santa Fa wrkshp, 5/8-10/95 8 May 1995 SOME CEBAF STRENGTHS AND ASSETS

World class staff and facilities in srf and cryogenics • $20M srf and surface science lab • Successful tech transfer to and collaboration with industry • Doubled the world's supply of sub X helium A working accelerator as test bed and "reality check" Outstanding expertise in conceptualizing, designing, building, and commissioning; integrating many disciplines: accelerator physics, engineering, software, operations Achieving technical success on cost and schedule through effective project management

V. JSL The Continuous Electron Beam Accal&rator Facility lis [cwltalks]Santa Fe wrkshp, 5/8-10/95 8 May 1995 /-WHY SRF IS SO ATTRACTIVE

• High gradients (5 to 25 MeV/m) in cw mode of operation c Reduces capital cost of structures • Minimizes site space requirements • Reduces impact of wake fields/HOM impedances on beam • Low wall loss (Qo ~ 5 -109) • Reduces operating cost • Reduces rf power capital cost • No need to push shunt impedance r/Q, allows large bore apertures (kr~1) • Combined .with damping leads to excellent HOM performance • Improves condition for low loss operation • Applications that rely on these qualities • TESLA • FEL • Intense proton beams

v-^gg^^— ——:—_. « J 7/7p Continuous Electron Beam Accelerator Facility lls (cwltalks]Santa Fa wrkshp, 5/8-10/95 8 May 1995 CEBAF FEL SALIENT FEATURES

9 Recommended application of srf technology (Industrial Advisory Board) • Intended use: large volume, industrial processing with UV light

• Organization: industry-led consortium assures customer and end user focus

9 1 kW UV Demo: a test bed on CEBAF site on the way to develop 10OkW UV capability • Funding: federal, state, and industry

V ML The Continuous Electron Beam Accelerator Facility lis [cwltalks]Santa Fe wrkshp, 5/8-10/95 8 May 1995 ^•^••^•MlilSllii..;:' •^m^ Ms«$ay- zz^mmmm^ssS*5-?.»S'--S5i .

CEBAFS FREE-ELECTRON LASER A Unique User Facility Struggles to be'Born

University of Illinois. Argonnc National and Norrhrop-Grumman into partne^shio Laboratory, and die- Nadonal Bureau of wim CE3AF and several SURA univcrsirie;. Standards, die contract went in 1984 to a induding Virginia Poiytcchnic Institute. consortium, the Southeastern Univcrsides Kamptan, Old Dominion, die College of Research Assccarion (SURA), now number• Wifllam and Mary, and die Univcsiries of ing 41 'academic partners. Construction DckwafafjVirginia. and Nora Carolina Sate. began in 1987, and me first espeoment took Tbgcriicr dvrse enddes fotmuiatcd a ptooosal place last year as scheduled. that CESAFs superconducting tadio-treauen- Currendy CEBAF has asdenrinc and cif avida be employed as a driver for Jiigh- _ meal staff of 400. Fariiirirt indude das 100 powcr FELs; which could; supply, tunable, dean chenueal etching, a dun monochromaric fctscr light for industrial-scale film deposition bboraroty, high-vacuum dec- processing. A peer review by a-pan'd spo nsored tron beam wddes, and mote. Managed and byNASAAdmirusaatocDan Goldin fast year operated under a DOE contract by SURA, confirmed the sSgnfnrsnr, potential of the FEL ScssrKte examhing CSAFs suoocanouctng t»~ dicfacHitr 5600 million invest• Eghc for industrial processing, ailing die pro• bum cavities, wrteft *w«y <*** me pfarwao* *w- ment by die federal government, die posal *a mode! for an mdusxcy/nadonal labo Commonwaldi of Virginia, me Gcv of rarory/univesary parrnrnhip." Newport News, several foreign contributors, o by observes, die Continuous and the US nuclear physics research commu• A "Wcaldi of Applications Electron Beam Accdcrator Fadlity nity. The 200-acrc she induces federal, sate. " As currendy planned. CEBAFs FEL fadii- T(CEBAF). located in Newport News. and SURA land. ty would provide 1-5 kW oflaser fight broad• VA. might seem to be a complex laboratory BVynmngm 1990. CEBAF has idcndSed ly mnabtc over two wavdengdi ranges: 1-20 with an obscure puie-scienee mission fikdy to ways its technologies could be exploited for pn and 190-550 nm. Consordum industry bar it from any dual-use' role. In (ace it industrial development. An Industrial members point to a number of industrial premises to be a unique example of coopers- Advisory Board (IAB) was set up to examine applications, some already demonstrated in don between government, acidemia, and how rhe faculty — its superconducting accel• rieir corporate laboratories using convention• industry. But as die budgct-curring noose erator cavities. reaJ-droc control system soft• al lasers. Among diem are: tightens around die Department of Energy, ware, accdesror-drivca Eghc source cryo- . * Surface modification of polymer film, CEBAF may be forced to 50 to the mat to Scnic systems, magnet technology, accelerator fiber, and composite products: secure its technology transfer future despite diagnostics, parade detectors, and data * Miuum-ichiningand surface finishing of its merits. acquisition systems — could parddpate in metals, ceramics, semiconductors, and As far back as 1976. physicists first envi• technology transfer iniriarives. One area sirt- polymers: and sioned CEBAF as a basic research laboratory gled out was a free-eJccnon laser (FEL) user * Materials analysis and process monitor• to probe atomic nudei for an understanding .facility for materials processing. ing instrumentation: of die quark structure of matter. After devcP • The next step was tic formation of a Laser •But die experience of membcrs-often is opmcrit of a •preliminary -dr-ngn. die'DOE Processing Consorrium, which brought such that in-bouse lasers are nooadequate to'mak• called for proposals. In a comperirion -rmh_ ' leading US firms as DuPont. 5M. IBM.. ing riiesc applications commercially viable — the Massachusetts Institute of Technology/" Xerox. ATScZ Newport News Shipbuilding, rhus their interest in a user EtcShy; According to rhc CEBAF sources, its FEL fadlity could Superconducting provide laser usht for process devdopment Driver Accelerator and testing at high power, lower -unit cost, and more tunabilhy than those currendy sraibbk. In addirion, it would funhcr the ^^H^^HSS advance of high-power FELs dicmsclves covmu comiut-M iitmuon. Consorauni manben who currendy use wcr diemtstry to impart spedftc surface prop- <—8 i 1 r -i 6- S^S±^ erdcj such as adherence and compatible met• allization charactcristia to polymers have found diat decp-UV radiation using exdmer LR Wiggler UV Wiggier lasers is a workable alternative. Patents have (53 m) • (2.4m) been obaincd for laser processes, all with hidi marker potential given a powerful indus• .208 ft. trial ksee. to do die following: K (64 m) * improve the adhesion of meals on poly• mer for decronic applications: A scoorarc v*?*- tjl r>e byos. cl me p-oocseS trve-eis^zr. sssr 3/ CS3*f. * imorovc the adhesion of polymer dims in packaging applications: and funding initiative faces an uphill bardc in the But for Frederick Dylla. CEBAFs • Add microtaxturing to fibers and film current fiscal climate. On December 20 Technology Transfer Manager and also man• for better adhesion in composite Energy Secretary Hazd OTcary announced ager of the FEL program, the spirit of collab• products, improving their efficiency as a chat the department will cut SI 0.6 billion oration that marks CEBAF's tics with state filter material. from its budget over the nest five years. and local governments and its industrial part• Of interest to consortium members who Within the department; it has been die Basic ners make it a first-class example of the kind manufacture semiconductor, photonic, and Energy Science (BES) directorate that has of project thar enhances US industrial com• magnetic materials would be the high-avcr- funded die development and operation of petitiveness and leverages existing national age-power infrared laser lines. They would existing synchrotron ught-source user facili• laboratory resources. More important, he make possible important nonlinear spectro• ties, and BES underwrote the NAS review. But says, CEBAFs industrial partners believe this scopic techniques with these applications: the directorate received SAO million less than to be true. CEBAF and die consortium part• • Basic characterization of complicated requested for its fiscal year 1995 operating ners will continue working with DOE and materials growth processes; budget, and existing BES user facilities want other federal agencies on a funding plan • Ptoduajon-qualirjr control monitoring: and to increase their budgets to meet customer because, as he purs ic "the project is such a • Nondestructive testing of intermediate demands. So the oudook for any new DOE wonderful idea, it is not a question of Sfiz will or final products. money for CEBAFs FEL is at best uncertain. be funded, but only of mien." • Commitments from consoraum indus• tries, the Commonwealth oFVupnia, onivcr- • sides, and the Cry of Newport News already total S27 nuHion. The state has pledged S5 million and Newport News S12 million for an Applied Research Center building, and industry in-kind contributions total 510 mil- Don. A conceptual team is at work to opti• mize the EEL design; •with industry partidpa- rion, it aims to minimize cost and technical risk*- provide reliable cost and scheduling esti• mates, and prepare die final design report. •Work that will accelerate die projects com• pletion when fully funded has begun at CEBAF and in die laboratories of both indus• try and university members of die consor• tium. With Commonwealth, funding, FOR EVERY DETECTOR. CEBAF is constructing a continuous-wave photocmission electron gun, a key compo• nent in die FEL driver accelerator. The tech• A HIGH VOLTAGE POWER SUPPLY nology is also used in CEBAFs main acceler• ator, dedicated to nuclear physics. At the THAT MATCHES PERFECTLY. same time DuFonc is funding laser applica• Bertan is the world leader in detector tions studies at rhree consortium universities, high voltage power supples and can meet ' the Aerospace Corp. is collaborating with virtually every deteaorrequirement. from CEBAF on FEL micromachining applica• lab to OEM. We can give you everything tions, and several CRADAs for FEL-re!atcd from regulated modules that are as design studies this year are being negotiated inexpensive as unregulated supplies, to with consortium industry partners. highly regulated instruments. Whichever you But in spite of possessing all die ingredients choose, you can be sure you're using the industry's standard for performance and THE for apparent success, in particular die crucial reliability. In feet, we have MTBF success cooperation between government, industry, stories that others only dream about MATCH and academia, the project has yet to receive a WhaCs your application? commitment of federal financing. The Laser Photomultipiier tubes, proportional •RS. Processing Consortium puts die total antici• counters, avalanche photo diodes? pated federal cost at about S27 million for a Miaochannel plates, channel electron diree-ycar construction project for die laser multipliers or image intensifiers? system. Call Bertan because nobody knows high voltage power supplies like An Uphill Battle Bertan Our units are being used A recent National Academy of Sciences across the board in research and review pane! recommended that the DOE industry. This unparalleled fund a user facility operating only at far- experience means that our people can help you get the best match of infrared (10-1000 micrometer) wavelengths. power supply to detector application That groups mandate was confined to the Ask for our.fxee 102 page reference study of facilities for scientific research alone, manual and catalog, "High Voltage not industrial applications, but sources at Power Supply Solutions". Call or CEBAF fear that the report's impact will write. Toll free: 800-966-2776. reach beyond its mandate, creating further lnNY:516-433-31I0.Fax: obstacles. 516-935-1766. Bertan High Volume. TKEHIGHVODXGEPEOPLE W Surely, ar.y new Dcoartmcnt of Energy Hicksvilie.NYUBOi. FEL BACKGROUND SUMMARY

• There are industrial applications for cost-effective, high-average-power UV light sources 0 There exists technology to build these light sources: • Superconducting radio frequency (srf) driven FELs 0 The Laser Processing Consortium was organized to develop, test and apply high-average-power FELs • There is a program plan: • Phase 1 UV Demo: • Focus of present request to DOE for 3-yr, $27M construction project • Significant project assets from state ($5M), city ($5M), industry ($10M) • Phase 2 Industrial Prototype (future: 5-7 years) • Scaling of Phase 1 effort: higher powers, higher reliability, lower cost

.41.

I lls 77)0 Continuous Electron Beam Accelerator Facility fCWLlalks] CEBAF at a Glance/EH visitors 20 April 1995 FEL USER FACILITY LOCATION ON CEBAF ACCELERATOR SITE i t> NORTH Machine Control Center

To o o South Linac / L FEL User Facility Self-contained, using CEBAF infrastructure and assets L. Nuclear Physics Experimental Halls

i i J L 0 100" 200" 300" 400"

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111 Wiggler UV Wiggler (5.3m) (2 Am) I—10 m ^ 190 ft. (58 m)

L »»0»IIIIWl I" T»l »W>WWI DyllVUVfel/ccb.fel.clemo.lyol.IOC jin 3/29/95 U¥ DEMO PERFORMANCE

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- : Exc^^lHawHH^HH^^^^^H Q - 0- -nHNI^HU^^^H 102 103 104 Wavelength (nm)

M«III- EXPERIENCES AND LESSONS LEARNED ^"ORIGINAL WORRIES" AND THEIR DISPOSAL-^

• "You can't change the design radically when you're that close to project approval" • Yes, you can • CEBAF's long term future derives from that change • "HOMs in srf cavities will lead to multi-pass BBM making recirculation impossible" • • Work at Cornell, DESY, CERN: HOMs damped to levels comparable to . copper cavities • "Frontal assault" (a few 102 Cray X-MP hours) demonstrated that CEBAF currents are factor 50 below threshold 0 "2K sub X operation will lead to troubles with 'super leaks'" • Never saw a 'super leak' • "srf is a lab technology, not ready for application" • Focused R&D and tech transfer led to four viable commercial bids for cavities

The Continuous Electron Beam Accelerator Facility ' lis [cwltalks]SantaFewrkshp, 5/8-10/95 8 May 1995 r ACTUAL CHALLENGES AND THEIR s RESOLUTION • srf: problems with leak-free assembly at start-up of mass production • Stopped assembly; focused on solving problems • Developed ultra-sensitive leak detection methods; all leaks were detectable at room temperature • Proceeded to produce on schedule 2 cryomodules per month in '92 & '93 0 Cryogenics: problems with cold compressors and matching 2K section to 4K section delayed start-up, forced work-around • All problems were in execution, implementation, and subcontract management; not in technology or concept • Today plant performs flawlessly at 2K, 5000W, 96.5% availability last year, and is completely under computer control, even for pump-down * Computer control: • An in-house system, excellent for small systems and start-up, was not up to full task; migration to EPICS while commissioning successful

The Continuous Electron Beam Accelerator Facility lls [cwltalks]Santa Fe wrkshp, 5/8-10/95 8 May 1995 r ARE WE ON THE WAY TO A UNIVERSAL v CONTROL SYSTEM? • Control system "Standard Model" has two network tiers • Operator interfaces and high-level applications • Device control • EPICS general- purpose low-level device control software has been developed by a multi-laboratory collaboration • Invented and pioneered by LANL • Large-scale application at CEBAF and Argonne's Advanced Photon Source (APS) • Planned for use worldwide • Being adopted rapidly for telescope controls • Consensus: analogous development possible for high-level control applications • Momentum building for defining a "software bus" to facilitate applications exchange

$tp£^&^&IF~mmi * ' -»-^»'""-" »'•'" -™ • ' ' "•• ' * The Continuous Electron Beam Accelerator Facility ' lls [cwltalks]Santa Fo wrkshp, 5/8-10/95 8 May 1995 r MISCELLANEOUS LESSONS LEARNED • The world of classical physics is predictable • Right calculations, right specs, right executions, right set-points, equipment tracking set-points: beam is on! 0 You get what you pay for • You can spend up front on R&D or later assign contingency; risk analysis tells you what is better • You succeed ih the areas that scare you • CEBAF's srf: only system needing no contingency assignments ° God (or the devil) is in the detail • Most problems causing delays in construction and ops are basically trivial 0 You've got to move fast to succeed • Optimal funding scenario: enough up front R&D; then build at a challenging pace 0 Technology is only a small fraction of success • Execution, organization, people will dominate issues 0 The myth of "off the shelf" technology • There are only "off the shelf" designs • EPICS is "off the shelf" technology: we still employ 20 software people

imftuj»iu»iin—IIWIWI—miw miummmmimmmmmmamotwammmaammmmmmmmmmf The Continuous Electron Beam Accelerator Facility lls [cwltalks]Santa Fe wrkshp, 5/8-10/95 8 May 1995 f-AN OPINION s

• If an accelerator is the right approach, a superconducting accelerator is superior 0 . Superior because of: • Lower power cost • Lower maintenance • Higher availability • Lower activation • The technical, cost and schedule risks are readily managed • Develop baseline design with cross cutting team (from R&D providers to end-users) • The necessary R&D infrastructure is in place in the US • With early industry involvement, the srf linac portions are readily built in 3 to 4 years

^^^SAF- !—•—— ' The Continuous Electron Beam Accelerator Facility lls [cwltalks]Santa Fe wrkshp. 5/8-10/95 8 May 1995 SUMMARY

9 " Reaching" in the high-tech direction enhances chances of success

• if the APT is worth building, it's worth building it right: Make it superconducting

• A properly managed, collaborative R&D effort assures success

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Spaltung UU ^ RETTf1 SLOW NEUTR. • langsames Kettenreaktion durch Neutron moderierte Neutronen U-235 Spaltung des angeregten Kerns KI82/BQ82-40 Pulsed Spallation Neutron Source General Setup

Synchrotron or H -- Source LINAC Compressor Rings (» 50 Hz)

Target

Pb, Pb-BI, U238

long pulses (« 1 ms) short pulses (« 1 u,s) Experimental c L stations ^ „ £ A? , ^£ tb-Z>L£ t 'A VM LAISLE Accelerator Options for the ESS

, 5 MW • ~ 1 [is pulse 50 Hz and 10 Hz Targets

1 Linac + Compressor Rings

2 Linac + FFAG

3 Linac + RCS

4 Induction Linac

5 Kaon Factory (50 GeV) SPECIFICATIONS FOR ESS

5 MW AVERAGE POWER AT TARGET(s)|Lf^ average thermal neutron flux comparable to high flux reactor ILL

~1 JUL SEC PROTON PULSES (100 kj, peak power,about 30 x higher than ISIS)

10 AND 50 HZ REPETITION RATE

TWO TARGET STATIONS

A MAJOR CHALLENGE H Linac normal or superconducting high energy structure

5MW,1 .334 GeV, 50 Hz, dc» 6.6%, X =Umsec I = 3.8 mA I = 100 mA

TWO 1.334 GeV, 50 Hz ACCUMULATORS T=1.9mA 60 ]iA FOR OTHER !=100A

MUON V •m- HIGH POWER BEAM DUMP

3rd target with msec pulses 14 50 Hz TARGET from Unac? \ « * / Nr. of partFctes: 2.34-10 / ring T = 600 nsec °rev.

Tb -j = 240 nsec voids . > pulse- length : 360 nsec 1000 turn injection circumference = 163 m

10 Hz TARGET

EUROPEAN SPALLATION SOURCE G, frees fp

1.25 KD (Coy^fl- 4>;ff»*j)

H°(N^S

•: V4

PREFERRED OPTIMISED H" INJECTION SYSTEM / 0 00 fZiy '.;.. jot/,'en I SCALED ESS LAYOUT

SCALE 1/2500

ALL DIMENSIONS IN METRES

200 750 EQUIPMENT BUILDINGS BEAM LINE SUPPORT CONTROL .".ROOM SERVICES ft R:1:NG. P/S 10 Hz TARGET 50 Hz TARGET MUON FACILITY ENGINEERING SERVICES WASTE HANDLING FACILITY BEAM DUMP SCIENCE BLOCK VENTILATION BUILDING

2 ms TARGET

ACCOMODATION TWO 1.334 GeV ACCUMULATOR ADMINISTRATION . RINGS

COOLING TOWERS

H° FACILITY

1.334 GeV LINEAR ACCELERATOR

ELECTRICITY SUB-STATI ON

.•{••• SECURITY EUROPEAN SPALLATION SOURCE SITE z y ^v $ iudi ^y pro f0 ->ui

£ Z.* ft

Project Assistant: M. Spatzek, KFA

Costs: F.H. Bohn, KFA Science Coordinator Project Leader: Sofety: NN J. Finney, RAL H. Lengeler, CERN Parameter Committee K. Bongardt, KFA . H.Conrad, KFA •: Q, Rees, RAL ff»t»"H'F' HWI()|ll>W^^W •linn ' ii •••••« ii

m—m Llnac Linkman Linkm.an Targets H. Klejn, Univ. Frankf. K. Bongardt, KFA Gardner, RAL -, H. Conrad, KFA H. Sleohenmesser, KFA

!S""BB"*' J Foreseen Scheme for ESS Linac

RFQ1 ; 50 KeV 175MHz RF0 2 70mA High Energy ^^ ^^50 MHz Linac nc.:7Q0MHz Bunchrotator Chopper ^^/^ ,punnel sc 350 MHz E-ramping 2MeV . < s^w RFQ2 70MeV 1334 MeV Accumulator Rings. Injection by RFQ1 H"- stripping „ Fast Chopper r .^erae-mA ••. (2rings, 2x2,5x10 ppp, I=80A) LEBT Wropulse-f^ insuiui tut AUIV/Qwentutt? r-i/ycam, vtuvtttsucti naiwuti n. i\H$t.t>l Source requirements for ESS

1. CURRENT Q

>70mA f ~ 2 **>"

2. EMITTANCE o I / * a) after RFQ I:

Wm«><0.3xmmmrad

b) end of Linac (1,334 GeV, py = 2.3):

< £(norm,rms) t37rmmmrad

Ap/p=±10-3 in tails only +5-10"5 particles with energy deviation > ±0,5MeV

3. PULSE SHAPE chopping: rise time: 10-20 nsec prechopping at ion source: ?

4. Low NOISE rippfe < 1 %

5. HIGH RELIABILITY AND AVAILABILITY rf - generafiinig; of plas#¥a

fact ayrhonrto e-Vf #w£i rfiToftinn eve^tom «c * Oh YC t ^o vA ? L p

Oc to ly( ?

Hoi ->h.h _s/ ^U Qy4 I * Jf -\^» J \j V^ *#•»%•"• >-*• W*_^ • > «« W«# 4. ' V- • \^J f v

Schematic drawing of the HIEFS

Insulator Ground Copper electrode

• -T-':ir.xt^*'. Ceramic Filter magnet Water

Magnet Anode

-•»ax2*.•£ .-j^^vsW^^'--^^-

Gas inlet ;^£S»2£K3

B,

:3S S^HH jriwS ££££ iytvj ?£.-"?§>• £sillf r^^T^T"^? Cathode Solenoid

Plasma electrode 50mm Screening electrode K. Volky T. Ludwig InstitutfurAngewandte Physik Expected emittance

Best measured emittance with the HIEFS

for atomic gas:

snor, 4nns, 80% * 0,OG3TC mm mrad

[9mA He+]

. for molecular gas: Snor, 4rms, 80% * ^,01% Him IDTad

. [4,8mA N+]

Realistic estimate for H" Snor 80% ~ ^'^7I mm mra

Li. aa^aHMM<- o UJ O" & 4v r*1) +. J! + X O

• k ao t ' ., oo +

(0 <—1—H —J—1—1—1—1—H—I- H—I— re [•n"B] ;^ISU9;UI [n-B] ^IISU9;UI vt fur Angewandte Physik, Universitat Frankfurt A. Maaser Schematic drawing of the H" source Copper 40° Bending magnet Water Plasma Screening electrode Insulator electrode Ml Ceramic

~usp magnets Dumping tube (90° bend)

Hole for sparking Ground plug electrode Institut fur Anaewandte Phvsik A.' Mssaser- H-SPECTRUM

UEx = 8kV IES = 1ft

* •

H"

.eg.

impurities

A/£[u} Layout for the 140mA D+source

field strength in the gap [kV/mm] luuitk radius of the emitting hole [mm] [5,5/ Op* 6 emitting area [cm2] 0.95 - . gap distance [mm] 13 aspect ratio 0.42 extraction voltage [kV] 65 extraction current [mA] current density [mA/cm2] rms emittance [-K mimmradj. <0,1 CtcLi Beam trajectories for a 65kV f4&m& D^ fe^pi plasma screening ground electrode electrode electrode ' IOUN 3.109(C)t 992 R.BECKER. BASED ON EGUN(C) 1988 W.BJHEF m emitting area

20 40 60 80 100 120 140 160 180 200 220 240 deuterium Instttttt fur Angewandte Physik, Universitat Frankfurt K. Volk D+spectra

UEX = 20kV lEX = 20mA ~^ bo ^ A A V- "#

13

CO c (D c

r _i «. 11

^ P. GroO. IAP Frankfurt

LEBT with Solenoids for ESS (Space Charge Compensated)

30

25 - decompensated ,ast ] ° cm decompensated

0 200 400 600 800 distance /mm two solenoid match: 70mA, 50keV H", 8^= 0.1 mm mrad

Source Output: r = 8mm, r' = 66mrad RFQ Input': r = 1.5mm, r' = 60mrad

. Transport Solenoid 1 S$len$id:2.. selffocussing 0.377 T &m¥ • compensated 0.391 T 0.3S5T . last 1 Ocm decompensated 0.320T. 0:495 T decompensated .0.480 T ' 0.562 T

Design Aspects:

Transmission Stripping Rise Time Emittance Growth Nonlinear Focussing Instabilities Charge Redistribution Dumping Neutrals Electrons Head of the Beam Pulse Steering Diagnostics P.Gro0.1APFranklurt LEBT - preexperiment: He+, lOkeV, 2.5mA

Comparison of beam parameters:

I W P K A

Similar beam dynamics concerning space charge effects

10 cm

>-LEBT similar to a simple ESS LEBT (without steering) 4 x^esiauai uas ±011 Energy Anaiyser

>r

r..«37.5 mm

160 The compensation process - different stages

•uacoaipeasated: c=0 paraai compensated: 0

SOOH

100-

radius [mm] Selfconsistent state for homogeneousdistributedBIf TcE=2 -5 eV, pe{r=0)/ phl{r=0) = 2-5,'T^GACRGI =0J.5m. rms-emittance growth due to charge redistribution

JL 2 _ K 2 £ (x ).^U

for <^V ? -Comi X. . K •

with generalized perveance K ... 27T€Qf3-5_c^'y:im A

Assagrarog 70mA, .50 keV H"

fid* VOL M j-Oi' —"*> f^£F& en,rms — OTUm ini

ctewgjiing from gausslan. to homogeneous S'n^ip'e;:

££=- 1 JL KJ^)- 0.038=6 „ •'.-. ti 2 ef F.-GroB, lAP'Franklurt Emittance Growth due to Decompensation of the Last Drift (55keV,70mA IT, PARMTRA Simulation)

100 100% RFQ input: KV-Distribution 0.1039 *JVJ 95% $ = 0.1 mm mrad 0.1038 98 90% £f= 0.1 mmmrad o 0.1035*

0.1045 •i 80% 0.1039 •i 70% [ 0.1037 m 50% -100 i I I i \ i \ I i I'll i i i i| t i I I i 1 i I i | i 0.1036 -2 -1*0 1 ' X [mm]

100 RFQ input: initially Gaussian beam :.:ioo% f 0.1611 and 5 cm decompensated li 95% • 0.1398 last drift. : sis 90% o •0.1180 £; = 0:1 mm-mrad- g^85% I 0.1010.. er = O'.'l 6.-mm-nirad. Hi 80%- |- 0.0878 H 70% 0.0676 -100 » 50% 0.0432

Emittance growth rates for initially Gaussian beam and decompensated last drift. & = 0.1:mmmrad

0 2 4 8 10 P. GroO. 1AP Frankfurt

Source Emittance: Measurement and PARMTRA-Input (10keV,2.5mA He+, compensated, 108mm drift)

Emittance measurement Density profile calculated fix)m emiftance measurement

€*_ Tim OV T00%« 0.0085 •*-S 95% 1400 250 0.0060 0.00 1200 j

PARMTRA input (10000 particles) PAKMEKA input dJsoQSit^proJSle.

100 100% 0.0114 •m 95% 2500 f 0.0089 m 90% a 0.0077 E 2H 85% 0.0067 • 80% -50- 0.0059 m 70% 0.0048 -100 09 50% 0.0032 -5 0 5 10 X [mm]

Simulation input is in good aggreement with measurement! /)»•:// -# So hn.MO*:ft- i**m ]**v+*\

Hl+jJOM/ftiSinfl

Da to t

0./ - / AiH^

OCLh & C C CV 05014035 30 I"" "'" i1 rTTTTT-TTT-m e**» *1000

20 7 -1.00%: 1.1-8.3'-

10

XI o 85%: 62.2 X

•10 30%: 52.7

-20 70%: 37.6

50%: 20.5 -30 i '••• •,, • • * • • •« -20 -10 0 10 20 X [mm] LEBT Conclusion / Questions

• How to estimate and minimize the length, of the final decompensated drift ?

• How to model a magnetic LEBT for intense beams!

• How to handle secondary electrons?

• How to dump neutrals and stripped electrons?

• How to handle front end of the i&ajeffQ?^uil^f? • How to handle steering ? • How to measure 'real' RFQ-input emittances?

• How do 'rqal' RFQ input distributions effect the RFQ output?

Detained experimental investigation necessary! I-

I Example of parameters of the ESS-injector-RFQs

RFQ1 RFQ2 or RFQ2 f [MHz] 175 175 350 Tin [MeV] 0.05 2.0 2.0 Tout [MeV] 2.0 5.0 (7.0) 5.0 (7.0) L [m] . 2.9 5.5-.- ' 2.9' Nrf [kW] 350 700 350 Nbeara-"' [kW] 100 150 150 Ilim [raA] lOQ. , 100 200 , , Funneling

Without funneling the ion source has to deliver about 140 mA with the required good eraittance, and the RFQs had to accelerate the full current. The preferred frequency would then be 350 MHz from the beginning to avoid a second frequency jump. This scenario is not impossible, but funneling relaxes the requirements for ion source and RFQ, promises a better beam quality and low emittance growth, allows the chopping at 175 MHz and improves the reliability. The investment costs for the front end is nearly doubled of course, but this is a small part of the overall cost anyway. For these reasons we" propose to have a funnel section at about. 7 MeV, where the two beams with a 175 MHz time structure are combined to a beam on one axis with a 350 MHz time structure and a doubled beam current without intrinsic emittance growth (Fig. 15). Funneling [22] bas been successfully proven experimentally [23,24], but further work has to be done, especially for the deflecting and the rebuncher. cavities, for which the IH-structure is advantagous [25]. Starting, with a 350 MHz RFQ one could think of funneling also, if the high j3 linac is operated at 700 MHz; in this case the funneling could occur after 350 MHz DTL at a higher energy. In case of a superconducting high energy linac operated at 350 MHz, this option is not possible, of course.

RFQ 2 175 or 350 MHz

Fig. 15: ESS - Funneling line. Di, D2: rf-deflectors, 175 MHz, S : septum magnet, Q: quadrupols T: triplett, B : bunching cavity, 350 MHz.

DTL

The drift tube linac (350 MHz, 1=75 m, cavity peak power=13 MW) has 'to accelerate from 5 (or better 7) MeV to 150 MeV. It is in principle state of the art, a post coupled Alvarez structure has been considered so far, but a bridge or cavity coupled DTL or an IH-strucnire are also possible structures. D TL oOLK'fK ( M- ?«)>*+) fa ~:*&J*UU Y^: Sc^/yUJ £&F OT£.(.ro*A, ^eo/i/^J

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3 x X a 3 H<*J # (e**.o.)

-£ / S *zCuu./e C.U/

SHUNT IMPEDANCES 700 MHZ FOR SIDE COUPLED CAVITY LINAC

iff S.'-n'' • •

0.4 0.5 •0,"6 0.7 0.3 0.9 1.0

/?• CAVITY PRODUCTION TECHNIQUES

ESS-linac 70 -1334 MeV : approximately 3S00 cells; material : e.g. OFHC Cu

5^JW#

iP^ODUCTION SEQUENCE: 1) Rough macliining of the cavities. / Forging of the . material. 2) Finish machining the cavities to frequency specifications (with iterations). 3) Finish cut of coupling slot and cooling channels (with iterations). 4) Fiai-sb machining side coupled cavities from rough macfeimg forgings (with iterations), 5) FiMisih side coupled cavity interface to match cavity

6) Braze cavities together to form tanks (several steps). 7>- Assembling subsections to form groups of tanks (bridge coupled sections). D(L\b COSTS / CELL

Option one,time 100 . 400 800 1200 charge MeV MeV MeV MeV machined $10200 $875 $1360 $1578 $1674 (700 MHz) +40 h. +24. k +28 k +30 h. +32 k forged $14500 $425 $675 : $soo $838

(700 Mhz) +37 h. +21 k +23 h. : +25 k : +27 k forged $41000 $3100 $ W>0 : $610© : $.6,404- (350 MHz) +35 h. +60 h. + 66h. +72. h. : +76. k

Remark: These costs are for a gradient |3 design, which means 10 minutes extra programming time per cavity. Non gradient (3 design would save only'^pOb^atiely 500h.-==> Ohl sx>

,U\ . Costs (MDM)

LOT AUTHOR: A.SI21C *2/2\/M 15l3»!lS CCL PARAMETERS

Input energy 70 MeV Output energy 1334 MeV Frequency 70.0 MHz Repetition rate 50 Hz Duty cycle / 6.0% Effective pulse current//? £ w c u c C> •* «w r 64 mA/Zt¥ Average current 3.84 mA . Accelerating gradient EAT 2.8 MVm Synchronous phase - 25 deg Realistic shunt impedance • '20...39MQ/m Transit time factor 0.83 Peak power beam 81 MW Peak power structure 113 MW Average CCL power' 12;MW Peak power per klystron for beam and strmete& 31W: Peak power per klystron including 30 % coBfrof IW' Number of klystrons 66. Number of tanks 264 Tank length 1.3 ... 2.0 m Cell number per tank 16... 10 Focusing doublets Quadrupole gradient 21... 15 T/m CCL length without/with extra sections for diagnostics 600/663 m Bore hole diameter 4.4 cm tune (deg) t^o 04 -P» cn CD \1 CO CD o o O O CD O o O

m to

* 1 1 GO GO GO X

PLOT AUTHM: A.SI2CC «i/;3/SS *«:5S:IS

£> 0 JO 100 1J0 200 230 300-

Fig. 7-3 Normalized, transverse rms emittance

0 50 ICO U0 200 2<0 500

Fig. 7-4 Longitudinal rms emittance

The eTnittances are obtained by multiparticle calculations of the coupled cavity finac. Space charge is taken, into account by summing up the Coulomb forces between the jnacrogarticles. The multiparticle calculauon shows a very well behaved beam -without rms ennttaace s-i-tywch- although equipartitioning is fulfilled at injection, only and the longitudinal time <$eg?ressi©B: is large at high, energies. This results in a much, smaller decrease "of the phase width, iisa* eSf^odL' from the zero current adiabatic datopinglaw. For the determination of particlss.lcigs^.fe-^e: CCL further work has to be done. —

The beamloading ratio is about 2. As the cavity response time is by a factor 2 faster man for the 350 MHz DTL additional 30% control power are foreseen for stabilizing the transient behaviour. Superconducting Linear Accelerator Cryo-Module

rf input couplers '/^ teoJLw) two-cell structures He ga* lein with tuning frame out

u • H-J in P.. .i, '„>., •"^r.';^^---iv -r" 'Li'—tr WW ^

about 7 to \2-:0§#% (according to/.fjefe)' ai^*?vr cu t ICLH a ffi^Sm&FBZ® »^to(i Gener^Ls^##

if input /,/„ /?/; ^ V y ^ Nb two-cell structure 3 S-Jfrfa

input coupler gate valve

tuning fram gher field. Due to the high loaded Q-value of a supercoildi^ag 'structure as given in Table 2 e increase of the fields during the time of the notch is rrw^'toaller for a superconducting an for a normal conducting structure..With superconductm'|'S'tr\ictures the required energy solution better than 10~3 can be reached.

p 0.43 0.57 : 0,79 . 0.90 ^peak'^acc 2.59 2.12 1.87 1.81 "peak^acc Oe/MV/m 52.2 44.9 34.5 34.2 r/Q n/m • 236 293 360 387 T - . 0.764 ; 0.751 . 0.737 0.732 Q (design) 3*109 3*109 . .... 3*109 3*'.l09 Qext 7.6*105 6.2*105 5.2*105.' 4.9*105 • QL . -V 3.8*105 ." 3.1*105 2.6M05 2:4* 105 Afl/2 Hz 458 564 675 .720 Afield ms 0.69 0.56 0.48 0,44 ,

EQT MV/m 10 10 10 10 .P-anaime>t

• Version A B C D Material Mob Niob Niob Nl^Sn Frequency MHz 352 352 700 . 700 Injection energy MeV 150 • Final energy MeV 1334 Opecafeg teHapecaiaase K 4.3 4.3 2 4.3 A^etageibimchicun:ent mA 60 rJDjity

•Peak rfjpower &>r beam MW " acceleration • 72 SEeakipower ofMystoons mvr 5 Number:dfstructunes.:pir 16, 14, > 1*16, 14, equal to equal to '•klystron 3*12, 18*12 A B" 3*10,12*8

:Number of klystrons 20 : Peak rf power in one input KW 465 300 465 465 coupler O 3 o ST r-t- o O . 3 o < o fl •-CD! r-t- v> CD J\ c^ P3 B o S4 fr -J ^2> < .s- < ~2 -"K» C s* fe <3

*. % - <<•

•< <3 r \*3 RF Control for TESLA TEST FACILITY (1)

O Goal: Develop design for RF control system which - -meets technical specifications (amplitude and phase stability) - is reproducible - is operable -is reliable - is well wratasfc**! =- ka^to-simpfe design for TESLA

#$$|j§§8g^ l®ite{«ar iioksown) range of parameters ' -^^B^m^im^sam^ caviity dynamics) i^e&oise - iTiniay^isim operable gradient (ttesholii for field emission, quench, HOM or fundamental coapter limitations) - component characteristics (phase drifts, failure modes, reproducibility, reliability) - calibration procedures, validity of calibration

0 TIF meeds extessive diagnostics and a flexible control system architectiare to ensure that system will be well understood. J..

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A> 9L/- ifra t fur e-S

TTF

by APTSCRF Team

High-Intensity SRF Proton Linac Workshop May 8-10, 1995

5/6/95 APTSCRF HIGH-INTENSITY PROTON LINAC

100 MeV

INJ RFQ CCDTL CCL

\ / \ 350 MHz 700 MHz

• High reliability and availability • High efficiency and cost-effectiveness • Existing technology • Low beam loss

Can an APT-accelerator system based on superconducting linac be a better system?

5/7/95 APTSCRF GOAL OF APTSCRF PROJECT

• Evaluate SCRF-hnac system in performance, risk, and cost • Define a SCRF-linac point design (above 100 MeV) to a sufficient leve! to determine: - technical feasibility - key technical issues and risk factors - cost drivers and estimates • Deliverables - a technical report » a point design ; » a technical feasibility assessment » a technical-risk assessment » a technology-development program - a cost report » construction and 40-year operating cost

5/7/95 APTSCRF PROJECT SCHEDULE

• February 1 Beginning of Project > March 1 Meeting at LANL > April 1 Meeting at LLNL > April 15 Strawman design complete

*» May 7 APTSCRF Workshop » June 30 Point design complete • July 31 Cost estimate complete •• September 15 Report to DOE

5/6/95 APTSCRF PURPOSE OF WORKSHOP

To review strawman design To survey SCRF technology worldwide for high-power proton linac application To gather design rules To improve strawman design To collect cost information To evaluate risk

5/7/95 APTSCRF OUTLINE OF PRESENTATION

• Strawman design • Issues • Design options

5/6/95 APTSCRF STRAWMAN DESIGN

Choices Reasons of choices

5/7/95 APTSCRF WHAT IS APTSCRF LINAC?

• It is a 10O-MW-class proton linac - high power - CW - proton beam - graded-p accelerating structure • It is different from most SCRF-linac application • It is a replacement of the normal-conducting APT linac above "100 MeV" • It is a superconducting linac assuming elliptical structures

5/7/95 APTSCRF APTSCRF LINAC PARAMETERS

Power = 100 MW Energy = 1.2 GeV Current = 83 mA Frequency = 700 MHz Operation temperature = 4.2 K

Injector NC Front End SC Linac mn>JWJ-

100 MeV 1.2 GeV

5/7/95 APTSCRF SIMPLE COST ESTIMATE

• Capital cost - RFcost = 198 M$ - structure cost = 112 M$ - refrigeration cost = 34 M$ • Operating cost per year - RFcost = 71.6M$ - refrigeration cost = 6.4 M$

Strategy to minimize cost - minimize RF capital and operating cost by choosing minimum RF power needed - minimize RF capital cost by optimizing $/W - minimize structure cost by using low beam energy and high gradient

5^7/95 APTSCRF BEAM POWER REQUIREMENT

400 •Q— Beam Power (MW) -*— Beam Current (mA) Beam energy 300- = 1.2 GeV - to avoid neutron 200- production inefficiency at lower beam 100 energy - to minimize structure length 400 800 1200 1600 2000 Beam Energy (MeV)

5/7/95 APTSCRF FREQUENCY CHOICE

• Frequency of 700 MHz instead of 350 MHz - advantages » better mechanical strength under vacuum load » less material cost » easier fabrication and handling » better match to front end - disadvantages » higher RF loss/bigger refrigerator » higher power density • RF loss of SC linac - 350 MHz, 4.2 K 8.3 kW -700 MHz, 4.2 K 17.1 kW - 700 MHz, 2 K 3.5 kW

5/7/95 APTSCRF RF-SYSTEM OPTIMIZATION

Minimize $/W with larger RF package - maximum coupler 400 kW couplers power - maximum klystron 2 cavities/klystron power 800 kW klystron Satisfy control requirement - minimize split per klystron

5/7/95 APTSCRF RF-SYSTEM ARCHITECTURE

800 kW Klystron

Circulator 3 dB Hybri 400 kW Coupler

Feedback Summation «

5/7/95 APTSCRF RF CONTROL SYSTEM • APT-Iinac specification - 1 degree phase and 1% amplitude regulation

Stability One Cavity Multiple Cavities per Amplifier per Amplifier 1 deg., 1% simple moderate <1 deg., 0.1% moderate difficult 0.1 deg., 0.01% difficult very difficult

Source: S. Simrock, CEBAF, "Experience with Control of Frequency, Amplitude, an'd Phase," Proc. of 6th Workshop on RF Superconductivity, 1993

Potential Sources of Phase and Amplitude Errors - Splitter imbalance - Thermal variation - Calibration errors - Beam coupling - Beam noise - Cavity tuning errors - Multipacting and field emission - Cavity coupling

5/7/95 APTSCRF RF-COST SUMMARY

Beam Power SC 92 MW Beam Power NC Funnel 100 MW Beam Power NC No Funnel 92 MW Beam Loading NCF Case 0.77 Beam Loading NCNF Case 0.68

Generator APT GeneratorHVDC PS AC Operating $AVFor Capitol Total Cost Type Type Power Power Power* Cost** Generator Cost Over 40 Yr (Millions/yr) Power (Millions) (Millions) Klystron (1 MW) NCNF 135 231 243 91 3.39 459 3,625

Klystron (1 MW) NCF 130 222 234 87 3.39 440 3,480 • Klystron (.8 MW) SC 92 157 166 62 3.98 366 2,465

Klystron (.5 MW) SC 92 157 166 62 4.82 443 2,465

Klystrode (.125 MW) SC 92 131 138 52 11.33 1042 2,060

Klystron Effc 0.585 Klystrode Effc 0.7

* .95% effic. for HVPS ** $.05/kWhr, 85% ava lability

5/7/95 APTSCRF RF-SYSTEM SUMMARY

• RF unit cost favors higher coupler power and klystron power • Cavity field control prefers single split of RF generator power • Primary RF architecture - 400-kW couplers - 800-kW klystrons - RF-field control to 1° phase and 1% amplitude stability - 3-dB hybrid coupler for added klystron protection • Secondary RF architecture - 250-kW couplers - 1-MW klystron split four way

APTSCRF SECONDARY RF ARCHITECTURE

1.0 MW Klystron

Circulator

3 dB Hybrid

250 kW • Coupler m H m m m w dJ

^ ] Feedback Summation

5/6/95 APTSCRF LINAC LAYOUT WITH A SPREADSHEET

• Guidelines - Make full use of power delivered by power coupler

- Follow maximum E0T as a function of (3

» Epeak = 16.7 MV/m - Smboth real-estate gradient to minimize longitudinal mismatch » constant real-estate gradient » match well with gradient below 100 MeV • Parameters - Power-coupler power of 400 kW - Synchronous angle of 30° - 30 cm/ warm-cold transition - Warm section of 1 m for diagnostic and quadrupoles - 32 cm for decoupling between cavities - Four cavities/cryomodule; 6-3 cells/cavity

5/6/95 APTSCRF ACCELERATOR PARAMETERS ALONG LINAC

3 T 700 T

E 2.5 •• S 2 -• •a

O 1.5 -• 1 -• HI Real St G (MV/m) 0) 0.5

-+• 4- H 200 400- 600 800 1000 1200 200 400 600 800 1000 1200 Energy (MeV) ,Pnai*nw /MM/\ 9 - 7 T 8 - •o 6 •• 0) CO 7 • -•"*/ - , | 5 "a 6 • > CO o 4 5 • o cells /cav 2 • • LU i use 1 o (MV/m) UJ 1 • •+- 0 • 1 1 1_ 1 1— 1 200 400 600 800 1000 1200 200 400 600 800 1000 1200 Energy (MeV) Energy (MeV)

5/6/95 APTSCRF APTSCRF CELL GEOMETRY

• Elliptical shaped cells at representative energies of 100, 650, and 1200 MeV • Similar shape as for PILAC and LAMPF "Afterburner" - elliptical noses and circular dome connected with straight-section sidewall • Beam aperture radius of 5 cm - two times of the normal-conducting design to minimize activation by beam halo • Nose-shape optimization criteria - low peak surface fields - mechanical constraints • Design consideration of intermediate-p cell - deflection of sidewall - multipactoring - fabrication am : APTSCRF CELL SHAPE AND PARAMETERS

_3.610 ln_ 9.169 cm yh X^es1.04i4 cImn R

7.362 in 18.700 cm 1.57 in_ 1.181 ln_ -4.00 cm 3.000 cm 3.15 in 2.362 in 8.00 cm 6.00.0 cm

1.969 in 1.969 in 5.000 cm 5.000 cm

100 MeV. 700MHz 1200 MeV. -700MHz

E (3 QO ZT2/Q0 Epk/EoT Hpk/EoT (MeV) (109) (Q/m) (A/MV) 100 0.43 0.645 180.4 3.42 5168 650 0.81 1.160 533.3 1.78 2813 1200 0.90 1.254 583.4 1.61 2682

5/7/95 APTSCRF CRYOMODULE LAYOUT • Cavity material: RRR 250 niobium • Operating temperature: 4.2 K • Four cavities per cryomodule (5 m) • Canities separation - greater than 32 cm for cavities decoupling - equai to (N+1/4)PX due to RF splitting • Bath-cooled cavities • Double warm windows - double protection - less multipactoring • Horizontal flange-mounted, LN-cooled, coaxial coupler - easy to fabricate, keep clean, and cooled - established technology i^i ' APTSCRF Los Alamos NATIONAL LABORATORY Engineering Sciences & Applications Division Cryomodule

'i9MMMr wvlMinlnlny

MM! ATM "K!A!A!A!A!A!/JJ8 DECOUPLING DISTANCE

• Coupling between cavities can introduce control problem • Coupling between cavities of aperture radius \ a by a beampipe of radius b and length h is

c Nb3

where the cavities have Ncells and coupling of/cc • To avoid coupling between cavities

kQL «1

where QL is the loaded Q of the cavities

5/6/95 APTSCRF kQLVALUES AMONG LABORATORIES

4/29/95 APTSCRF BEAM SIZE

• For SC linac, beampipe aperture can be enlarged without efficiency penalty • A larger beampipe-aperture radius to beamsize radius will minimize beam loss which is a major concern of APT normal- conducting linac • Assuming same quadrupole doublets as the normal-conducting APT linac, the matched beam size along the SC linac is calculated • The aperture to beamsize ratio between 100 MeV and 1.0 GeV is 20-55 for SC linac compared to 13-26 in normal-conducting linac

5/7/95 APTSCRF Issues

Coupler Cavity structure Reliability and availability Development program

5/6/95 APTSCRF EXISTING DATA ON COUPLER

• CESR at Cornell - Frequency at 500 MHz - RF tested to 340 kW, CW ; - Operated at 155 kW at 120 mA • HERA at DESY - Frequency at 500 MHz - RF tested to 300 kW - Operating at 60 kW at 35 mA • LEPH,CERN - Frequency at 350 MHz - RF tested to 200 kW equivalent, CW • KEK - Frequency at 500 MHz - RF tested to 800 kW CW

^ APTSCRF QUESTIONS ON COUPLER

• What is the achievable power capability for coupler likely in two years? • What should be the coupler scheme? - coaxial or waveguide • How can the coupling between the coupler and cavity be achieved? • How should we arrange the RF windows? - warm or cold window - locations and number of windows

5/7/95 APTSCRF CAVITY STRUCTURE

• Special problems with intermediate-p elliptical cavity - mechanical stress under vacuum load - peak field and gradient - multipactoring • Cavities per cryomodule, cells per cavity • Separation of cavities - coupling between cavities - compatibility with RF architecture • Miscellaneous items - tuning scheme - warm/cold transition

5/7/95 APTSCRF QUESTIONS ON CAVITY STRUCTURE

What is the lowest-p cavity achievable with elliptical cavity? What is the optimum frequency? 350 MHz vs 700 MHz, or others. What is the optimum cell and cavity arrangement in the cryomodule? What is the intercell coupling and field flatness needed? What is the alternate approach to elliptical cavity? - multicell spoke structure

5/7/95 APTSCRF RELIABILITY AND AVAILABILITY Existing Operation Data

HEPL - seven 1300-MHz cavities, 30,000 hours of operation TRISTAN, KEK - 32 508-MHz 4-cell cavities, 25,000 hours of operation HERA, DESY - 16 500-MHz 4-cell cavities, 15,000 hours of operation CERN (SPS) - one 352-MHz 4-cell cavities, 6,500 hours of operation CEBAF - 338 1497-MHz 5-cell cavities, 4,000 hours of operation CERN (LEP) - 28 352-MHz 4-cell cavities, 500 hours of operation

5/7/95 APTSCRF QUESTIONS ON RELIABILITY AND AVAILABILITY • How does the availability data differ between normal- conducting (NC) and superconducting (SC) linacs? • Is a SC-linac system more complicated compared to the NC-linac system? • With a larger beam aperture, can we relax the requirement on beam dynamics? • How do we recover from a quench? - What will be the cavity performance after a beam accident? - Can we operate with the loss of a cavity? - Can we replace cavities readily? - Can we adequately provide spare modules? • Is the SC linac a better system overall? • How flexible is the SC linac in the future upgrade?

5/6/95 APTSCRF DEVELOPMENT PROGRAM

• Tests without beam is well defined - two-year development program » similar program as for 805-MHz cavity • » single-cell RF tests » multiple-cell RF tests » power-coupler RF tests - facility available at Los Alamos • Prototype cryomodule tests - high power tests without beam - integrated test with beam » test cavity and power coupler at full beam » demonstrate RF control of cavity » obtain operating experience with SC module as part of a linac system

5/7/95 APTSCRF QUESTIONS ON DEVELOPMENT PLAN

• What is the definitive test that SCRF linac is viable for APT? • Is a beam test simultaneously demonstrating both the intermediate-p cavities and the high- power couplers necessary? • Where can such a beam test be carried out?

5/7/95 APTSCRF SPOKE STRUCTURE • Two-cell Spoke Structure at (3=0.3 has been demonstrated at Argonne National Laboratory

- E0T = 7.5 MV/m, Epeak = 60 MV/m, at 850 MHz • Advantages of spoke structures - high magnetic coupling

- localized high EpeakJ potentially less multipactoring problem^ - mechanically stronger under vacuum load * - ^ • Benefits of Spoke Structure to APTSCRF Project - early 100-mA beam test at the APT Front-End Demonstrator - possible backup for elliptical structure at lower (3 - flexibility in transition energy to SC linac • Disadvantages - distraction and possible irrelevance of tests required for elliptical-structure development program

5/7/95 APTSCRF 3-CELL SPOKE STRUCTURE

5/7/95 APTSCRF FRAME: 19/04/95 - 17:25:57 VERSION [V320.0] SP7M8.DRC

MAFIA 3D PLOT OF THE MATERIAL DISTRIBUTION IN THE MESH M--:3 .20 tt3DPLOT COORDINATES/M FULL RANGE / WINDOW XI 0.0000. 0.14200) ( 0.0000, 0.14200) Y( 0.0000, 0.14200] [ 0.0000, 0.14200] Z(-0.0020000, 0.41819) (-0.0020000, 0.41819] MATERIALS: 1,

PROJECTION: 0.5

Y X

V FRAME: 17/04/95 - 17:19:58 VERSION|V320.0] SP4M5.DRC

FREQUENCY/HZ 7.3962528000000E+08 MAXIMUM ERROR OF CURLCURL-E 1.1352833826095E-03 MEAN ERROR OF CURLCURL-E 5.2486182539724E-05 MAFIA MAXIMUM ERROR OF DIVERGENCE-D 3.1964961S22135E-07 TIME HARMONIC ELECTRIC FIELD IN V/M 3.20 #ARROW COORDINATES/M FULL RANGE / WINDOW X( 0.0000, 0.093000) ( 0.0000, 0.093000) Y| 0.0000, 0.093000) ( 0.0000, 0.0000) Z[-0.0020000, 0.30504) [-0.0020000, 0.30504)

SYMBOL - E_l 9.300E-02 < i \ i » » > Y-MESHLINE: CUT AT Y/M: •• ^ \ 1 It* INTERPOLATE.- LOGSCALE - » / i- *«- v \ i f / •* - MAX ARROW •• 77.808 1 t / 4.650E-02 _ - - N \ r / >K^< v - - / x \ ~m ^* f , \ x\-Wt»-/ f \ -« ** ^ > \ *>

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0.

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X

,+Y LB •> Options

• 700 MHz, 250-kW coupler - modest R&D effort on couplers - 1-MW klystron split two time - transfer risk from coupler to RF control • 350 MHz, 125 kW coupler - conservative design - closest to existing SC technology - R&D on klystrode • 350 MHz, 400-kW coupler - existing R&D program for coupler

5/7/95 APTSCRF SUMMARY OF OPTIONS

Coupler Generatoi Cry o- Length Average Power Power modules (m) Gradient (kW) (kW) (MV/m) 125 125 221 988 1.20 125 250 221 98 8 1.20 250 500 112 611 1.82 400 800 7 5 447 2.59

Coupler Capital Cost Annual Power (M$) Oper. Cost (kW) (M$) RF Unit RF Cost Structure Total Cost Cost Cost ($/W) 125 4.70 520 323 90 2 5 9 125 2.94 325 323 70 7 7 1 250 2.03 227 205 49 3 7 3 400 1.65 198 151 413 7 8

I

5/7/95 APTSCRF CONCLUSION

• Goals of the APTSCRF Project and this Workshop has been described. • A strawman design has been presented with issues and options to form the basis of discussions in the Working Groups • Discussions will be needed so that results can be summarized for the benefit of APT and other high-intensity superconducting proton linac

5/7/95 APTSCRF S UP&K Co Aft) u c T/A>£ C* C /T/£S

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NC Cavity shape SC Cavity Shape

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• Single cell to reduce power/coupler

• Waveguide input coupler * • • Large aperture beam pipe to reduce R/Q of HOM

to propagate HOM power out of cryostat

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49 High Power Window

Requirements -Ay CE$R~Jll Travelling wave power CW 325 kwatt Reflected power CW 125 kwatt Preferred aspects hidden from cavity line of sight located far from cavity field Would avoid x-rays from cavity lost particles from beam Working with two companies Premier Microwave Thompson BBB?**

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Needed for CESR-IH: 6 MV/m Single bunch current =11 mA Total beam current 1 amp [Window and Input Coupler

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Total loss factor of cavity/HOM loads/taper system = 0.4 V/pC HOM loads = 0.2, tapers=0.1, cavity = 0.1 Compared to CESR total loss factor: 10 V/pC

• Look for beam instabilities and resonant heating of HOM loads use single bunch current: 30 mA vary spacing between two bunches from 0.5 - 3 m Found none

• Look for beam instabilities and resonant heating of HOM loads use 9 bunches, total 100 mA vary frequency of HOMs across beam revolution harmonics Found none Outlook Need 4 SRF cavities for CESR-ffl All components successfully tested off-line and with beam

Refrigerator ordered one 600 watt unit to be installed in . Sept 95

2nd niobium cavity ordered - delivery June 95

Compact cryostat for tunnel ordered - delivery Dec yj

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i REPORT ON THE CAVITY-STRUCTURES WORKING GROUP OF THE HIGH-INTENSITY SRF PROTON LINAC WORKSHOP

May 8-10, 1995 Sante Fe, New Mexico

T. Wangler and J. Delayen, Chairmen June 19, 1995

SUMMARY

The following main topics were discussed in the working group: 1) Linac Architecture/Spreadsheet Studies, 2) Accelerating Structure Issues for (3 < 1 cavities, 3) Beam Issues, 4) Operational Issues, 5) Cryomodule Issues, 6) Alternative Approaches, 7) Upgrade Paths, 8) R&D Program, and 9) Advantages of the Superconducting Accelerator. The main objectives of the working group were to evaluate the strawman SC linac design presented in the earlier talk by D. Chan, to discuss possible alternatives, to identify outstanding technical issues,- and to propose essential elements for an R&D program. The basic task of the study is to identify a technically defensible superconducting (SC) linac system, which will become the basis of a cost estimate for comparison with a comparable room- temperature (RT) linac system for the APT project.

The working group found no technical reason, why the superconducting option could not be made to work, or might be impractical for the APT application. In fact in the opinion of the chairmen, there was considerable enthusiasm among many of the participants for the potential advantages that a SC linac could provide, including the prospect for significantly lower cost over a 40- year life cycle.

One of the most important recommendations for which a group consensus was reached, was that the superconducting design study should consist of two parts. As the first part, a SC design should be identified that is conservative, and as close as possible to the RT design in terms of the primary parameters (energy, current, rf frequency, and rf power source). This initial approach allows an easy comparison of- the two linac systems, which the group "believed would show that the SC design is viable, and offers some real

1 advantages, without claiming that the SC design is optimum. As the second part, it would be important to carry out a design optimization study to utilize, most effectively, the specific characteristics of the SC technology. The second part is important because SC opens up the parameter space that can provide increased flexibility and a wider range of design options. The final design may end up being quite different than the NC scenario both jh the parameter choices, and in the way the accelerator could' be upgraded. This recommendation for a two-part study, with the first*part corresponding to the present SC/RT comparison study, is consistent. with the time spate and the resources for the present study. _ ^f'":"„.

The second major recommendation was to replace the^basic module of the present "strawman? design-with a new bjisic JjBBd&dn<.which four cavities are driven by a single 700-MHz, I-MW^ystcpn,; as;.— shown in Fig. 1. This has the additional benefit of reducing _the nominal power-coupler requirement from ,400 kWfto.250:£W per cavity. In addition itwa|Fsuggested* that"two rf/drives pei^gavity would reduce the powef^duplerj^requirement?!) ,only.. 125 KW per coupler, a value that is* believed to be;already" attainable £with beam). This would essentially eliminate ffie-hlghrpower coupler as a significant risk in the. .design, and ;an R&T> program .would not need to advance the state-of-the" art for the ^T^ppUca^nv^i R&D program would be directed towards an_upgrade to rag^'power coupler performance, which would further Jncra^ could the

The choice of the elliptical cavity, which^ha^p^h-soisu^^sMlJfor

(5 = 1 applications, for the entire velocity range Q.£ <~;g :<,jf-Vas^ „ generally believed to be reasonable and workable^ Preliminary mechanical design studies for a p = 0.43 (100 MeV) elliptical structure showed that it looks mechanically feasible. M|ny believed that multipacting in the medium-p" elliptical structure was unlikely to be a serious problem. However, this could be confirmed very easily from laboratory measurements in the early stages of the project.

The issue of availability and reliability was discussed. Based on the present operational experience with superconducting accelerators, very few of the problems resulting in down time are associated with the superconductivity or the cryogenics. At CEBAF no long-term* performance concerns have arisen after 1 to 3 years of running. There is no evidence at present that says that the reliability will be much different for the SC accelerators than for the RT accelerators. CEBAF, partially commissioned, has reached 69% availability during the first year of beam delivery, and expects to reach 85% over a three year period.

The R&D program needed to address specific cavity or coupler issues was not believed to be significant problem, in terms of either the scope or the schedule, because the parameters of the new reference design are very conservative. Indeed, the APT schedule does not appear to provide time for very much real R&D, and therefore, the choice of a conservative design removes the need for a major R&D effort. The group believed that the earliest possible test of a single module with beam is important to eliminate technical surprises, and to reduce the risk of schedule delays. Such a test would involve cryostat, cavities, couplers, rf components, and focusing magnets, operating as a complete system. However, the method of conducting meaningful tests with 100 mA of CW proton beam within the required velocity range is not straightforward, because no such such beam source exists. The matter was not resolved within the limited time frame of the workshop, but alternatives were presented, and it was agreed that further study of this issue would be necessary before a final recommendation should be made.

At the final session of the meeting, a summary of the working group activities was presented by J. Delayen to the complete workshop audience. The vugraphs of that talk are included, along with a collection of some of the vugraphs presented in the working group. Not all vugraphs of all the working-group presentations were available to the chairmen, and for those that are not included the chairmen apologize.

LTNAC ARCHITECTURE AND SPREADSHEET STUDIES

A presentation was given by E. Gray on architecture and spreadsheet studies, emphasizing the strawman design that had been introduced earlier by D. Chan. This design was characterized by an rf module with a nominal 800-kW klystron that drives two multicell cavities. The number of cells vary from 6 to 3. There are 9 different cavity types, each characterized by a geometric (3, which defines the cell length. A of number points were raised in the discussion that followed. 1) The value of the maximum peak electric field is not simply a constant value (slightly more than 16 MV/m was assumed

3 for the spreadsheet studies) that is the same for all P values. There is a evidence for a gap-dependent effect that was reported by Bollinger (L. Bollinger, Review of Superconducting Ion Linacs, 1992 Linear Accelerator Conference, Ottawa, Ontario, Canada, AECL-10728, August 24-28, 1992, p 13), where the achievable field increases with decreasing gap. Another approach for choosing the peak field is based on an analysis of the density of field emitters versus Epeak> which was discussed'by F. Krawczyk. The latter approach suggested that.the fields we^had used in the study were conservative. There was-no statement that the fields had generally been chosen too conservatively. 2) There was no known reason why. a single cavity could not be driven with two rf drives, which ;w|ail4 lower the rf power requirements for the windows and couplers. 3), The number of different p types, 9 in the? spreadsheet stagg&s&as obtained. byr - assuming that the velocity range would be determined by allowing the"lransit-time factor of a multicell cavity .to, drop -byi 1%. It was suggested that this drop might be allowed to increase.. A large number of p values is probably favored by-the. -fbeam; dynamics, and by the rf-to beam-efficiency. A small number- is-favored to reduce the number of cavities to test, and to reduce the number of different kinds of spare modules, and cavities. 4) We have assumed that the longitudinal beam dynamics depends more on the^realrestate averaged accelerating gradient, rather than the gradient within the active region of the cavity. This seems like a reasonable assumption if the longitudinal,oscillation period is much greater than the structure period^ Qx^zp^o^^- Was jto k^eptfie^real-estate gradient— smooth, even tFou^|^,tfie3tfue^^ gradi^f^im|fifey3^ffb'm^avity to cavity. This assumplion^^[s^be^ested^ Jb^cpmjtfter SKnuiationft""-- and not enough simulatibir^Ss 'b^een^doneT^t^o^y'slua'te^^his- J; assumption. 5) A principle of "constant parameters wa#"suggested. The idea was to maintain constant parameters throughout the linac, and that in the long fun this would minimize the overall cost. It was agreed that this is easier to do for an electron linac, where p = 1 throughout. When p varies, as is the case for the proton linac, the principle might be modified by maintaining piecewise-constant parameters.

The discussion also yielded the following general conclusions. The cost of the rf power is the biggest driver for the total capital cost. Furthermore, the efficiency of the rf power system is the biggest driver for the operational cost. Because the final cost and the optimum choice depend so strongly on the assumptions made about the rf costs, it is important to determine a) how accurate are the if costs? b) what will those costs be in a few years?

As was described earlier, it was suggested that a SC design should be identified that is conservative, and as close as possible to the RT design in terms of the primary parameters (energy, current, rf frequency, and rf power source). The second recommendation is to replace the basic module of the present "strawman" design with a new basic module in which four cavities are driven by a single 700- MHz, 1-MW klystron, which means that the SC linac uses the same klystron as the RT design. This has the additional benefit of reducing the nominal power-coupler requirement from 400 kW to 250 kW. Nominal gradients of about 4 to 6 MV/m will be a conservative choice. Another optional configuration that was suggested was to combine pairs of cavities to obtain longer cavities that are each driven by two 250 kW couplers.

EUJPTTCAL STRUCTURE ISSUES FOR &

Short presentations were given by D. Schrage on the mechanical issues, and F. Krawczyk on the rf structure calculations. The main conclusions from the discussions about Elliptical Structure Issues for P < 1 are: 1) Preliminary mechanical design studies for |3 = 0.43 (100 MeV) elliptical structure show that it looks feasible. 2) Most believed that multipacting of the structure was unlikely to be a serious problem. 3) At 700 MHz and for the gradients being considered, there is no reason to go to 2 K operation. 4) With a loaded Q of 2 x 105,Af = 3.5 kHz, microphonics should not be a serious issue. It will be much less than at CEBAF. Low level .rf control of the group of four cavities is believed to be sufficient, but this issue needs further study, because the requirements for the proton linac are more strict compared with electron linacs, where most of the experience base is derived. This leads to-the-simplest rf system for an initial reference design concept. The optimum frequency choice depends on a balance of many issues. The 700-MHz choice results in smaller, and cheaper structures, which are easier to handle. This frequency also allows funneling of two 350-MHz beams, as an upgrade option. The 350- MHz choice results in fewer cells for the same length of structure, giving a broader velocity acceptance and more operational flexibility. It allows a design with no frequency transitions, which could translate into reduced beam-halo formation. This choice would lower the refrigeration requirements for a given aperture, but refrigeration

5 is not a significant cost driver. The recommendation for the study was to choose 700-MHz, because it corresponds to the RT choice (in accordance with the recommendation made earlier to keep as many parameters the same as possible). For a final optimization, the frequency question must be reopened and studied more carefully.

BEAM ISSUES C. Bohn and J. Lagniel gave short presentations on beam dynamics issues. Bohn concluded that there was less concern about production of higher-order modes (HOM) induced by the proton beam than by relativistic electrons. The HOMs cause concerns about extra-power dissipation in the niobium, and about possible field enhancements in the cavities that might introduce field emissions or quenching. S. Ruggiero concluded that the HOM power is expected to add about 1 to 2 W/m into the LHe, which is comparable to the expected static heat input. This was based on the assumption of a 1 mm long bunch. This suggests that the HOM couplers would not result in a major reduction of heat input into LHe, since the static load is not a serious effect in our case.

Another concern is the beam-breakup instability (BBU). Cumulative BBU is the main concern, where a displaced beam centroid can excite a cavity mode, which can deflect trailing bunches, leading to an instability. Bohn concluded that if QL < 106 that there would be no problem exciting this instability. It was pointed out that because of the expected fabrication errors in nominally identical cavities (even for the same design P), there would be a spread of resonant frequencies for the deflecting modes, and an effective broadening of the corresponding Q curves, resulting in effective loaded Qs for these modes of the order QL = 104. Thus, HOM couplers would not be needed for control of BBU, if, indeed, BBU is not a problem. However, it was suggested that ir would be prudent to assume that HOM couplers would be installed on each cavity. This would not affect the total cost very much, and it would reduce the chances that field enhancements caused by excitation of HOMs could for some reason limit the field. The main reason is to diffuse any concern that the design might not be addressing a problem that has been serious in electron linacs.

The distance between focusing elements must be kept short enough to maintain a significant beam-aperture to rms beam-size advantage for the SC design. A first pass at the beam dynamics on the strawman

6 design, based on a computer simulation with space charge, indicates the focusing in the right ball park, but more detailed study remains ^ to be done.

Another important issue is the deflection of the beam by the fields in the vicinity of the coupler. The relative placement of the pair of couplers can be used to cancel this efecL

CRVOMOMJLE TSSUES

A presentation of D. Schrage and R. Gentzlinger (presented by Schrage) outlined an approach to the cryostat design. Many requirements for the design had not yet been specified, such as the frequency tuner requirements. A "CERN-like" design was proposed. The main conclusion of the cryomodule discussion was that with sufficient care, the design of a satisfactory cryostat should not be an issue.

OPERATIONAL TSSUES

The starting point for the discussion of operational issues began with the talk by A. Hutton, which was presented to the full workshop audience. The discussion of operational issues resulted in the statement that, based on the present operational experience with superconducting accelerators, very few of the problems resulting in down time are associated with the superconductivity or the cryogenics. At CEBAF no long-term performance concerns have arisen after 1 to 3 years of running. There is no evidence at present that says that the reliability will be much different for the SC accelerators than for the RT accelerators. CEBAF, partially commissioned, has reached 69% availability during the first year of beam delivery, and expects to reach 85% over a three year period.

ALTERNATIVE APPROACHES

Alternative approaches were discussed. One recommendation was that because most of the benefit is at high energy, one should optimize the high-energy section and work backwards. Another question was how low in energy can we go with the SC section of the linac? This was discussed in a short presentation by J. Delayen. There appears to be no reason why the minimum energy cannot be at least as low as 10 MeV,. if one chooses. A spoke-cavity structure might be an ideal choice in the energy .range of about 10 to 200 MeV. Another

7 interesting alternative, suggested in a talk by Ruggiero, is to drive each cavity from a 250-kW klystrode. The high efficiency of the klystrode leads to a low operating cost, even though the capital cost is high (see the last column of Fig. 2). it was suggested that this alternative should be investigated further after the present study is completed.

UPGRADE OPTTONS * Four upgrade options were considered that could provide up to twice the beam power. 1) Build a whole new linac. 2) Double the if power in the existing linac, (double the coupler power capacity, and funnel) 3) Double the rf power in the existing linac, (double the number of coupler ports at the same coupler capacity, and funnel). 4) Increase the energy of the linac. Option 3 avoids the coupler-limitation issue by having two 125 kW couplers per cavity, each of which might be upgraded through an R&D program to 250 kW later. Option 4 could be achieved by adding more structure, or by increasing the field in the cavities, although the latter approach would not be likely to double the energy.

RESEARCH AND DEVELOPMENT PROGRAM

The discussion of the R&D issues led to several conclusions. Even so, at the end there appeared to be general agreement that this. subject was not yet in a completely resolved state. It was agreed that the R&D must be done early, probably within the first two years. Major technical questions must not be left unresolved later than this. There was no time to address questions of cost and schedule for the R&D. Generally, the suggestion to provide two power couplers per cavity and to reduce the maximum input power per cavity to 250 kW, means that the maximum input power per coupler is only 125 kW, a value that is considered-to-be achievable today, even with beam. This means that the new reference design that was recommended in this working group, requires no major technical advances in terms of required performance of the components. Still, there remains to be demonstrated, the performance of prototype cavities, couplers, and complete test of the operation of a basic module, including acceleration of the full-current beam.

The basic components of the laboratory R&D program can fall into four categories, 1) a single-cell cavity program, 2) a multicell cavity program, 3) rf-coupler program, and 4) an integrated test with beam.

8 The single-cell work would address mechanical and multipacting issues for the different design p values. The multicell work would focus on a) demonstration of the design accelerating field with adequate safety margin, b) demonstration of cavity tuning methods, and c) reconditioning tests after a simulated accident Finally, the integrated beam tests should test the complete system composed of cavities,' cryostat, magnets, power couplers, and a full-current beam. . One wishes to demonstrate a reliable performance at the design field levels, and explore potential problems such as those associated with operation of the whole system in the beam environment, including effects of secondary particles produced by the beam, effects of higher-order modes excited by the beam, and effects of higher-order modes on input power-coupler performance. It was felt that all of these issues have been successfully addressed for other projects in the past, and are not unique to the APT accelerator. The real purpose of this R&D is to avoid surprises, especially in the performance of the integrated system. The R&D is not necessary as a means to make major new technical advances, since the proposed new reference design remains very near the state of the art. Integrated Beam Tests on the Front-End Demonstrator.

Ideally, the integrated test requires a 100-mA CW proton beam in the 100-MeV energy range, but no such beam exists at present. Lower energy proton beams result in reduced transit-time factor, and reduced efficiency for transfer of rf power to the beam. Unfortunately, the transit-time factor falls rapidly with decreasing beam energy. This makes it difficult to test the power coupler with a reduced energy proton beam. Several beam tests of the power coupler on the Front End Demonstrator (FED) were been suggested, including a room-temperature drift-tube linac after the 7-MeV RFQ, a 7-MeV multicell spoke SC resonator, and a 40-MeV test of an p = 0.8 elliptical SC cavity .in. a. 3TT/2 mode (this also suffers from a reduced transit-time factor). However, the group concluded that it would be unlikely that even if any of these tests were technically satisfactory, the possibility of tests on the FED would come early enough in the program. Also, none of the tests that had been suggested were sufficiently representative of the real system to address all the issues. Thus, the group expressed no enthusiasm for the proposed FED experiments.

9 Other Ideas for an Earlier Integrated Beam Test

The only suggested tests that might come early enough were 1) a LAMPF beam test with the existing 805-MHz, 4-cell niobium cavity, and 2) a CW electron beam test. With the peak beam currents of 15 mA at LAMPF, for a £ = 0.9, 4 cell, 805-MHz cavity at 12.5 MV/m, and zero synchronous phase, we obtain 125 kW for the peak beam power, which is the desired coupler power of the new reference design. However, we would really like to provide a test with two couplers per cavity for a total of 250 kW for the cavity peak beam power. Also, assuming a 10% duty factor, the average power is only 12.5 kW. Because LAMPF is pulsed, the LAMPF test would "not test the power coupler near the desired high average power of the new reference design.

A CW electron beam might test the performance of the power. coupler at the actual average power level. Whether a suitable beam exists, or whether a small electron accelerator would have to be designed for this purpose was not answered. Thus, it may be that the integrated test issues can not be addressed in a single beam test. The issue was not completely resolved by the group. ADVANTAGES OF AN RF SUPERCONDUCTING LINAC

The final activity was to identify and discuss some of the advantages of a SC linac.

Cost Savings from a Superconducting Linac

There was complete agreement that the operational cost will be less for the SC linac. The issue of capital cost saving from SC resulted in more discussion. The rf system cost and the length costs favor the SC linac, while the cryogenic "system cost goes the other way, and the structure cost depends on the length of structure. Three initial capital cost estimates have been done independently, T. Wangler, M. Prome, and H. Heinrichs, and all three obtained a cost saving for the SC linac of about 30%. It was agreed however that the uncertainties in all three estimates are large, and these results, while suggestive of a favorable capital-cost result for the SC linac, are not conclusive. It should be possible to obtain a good capital-cost comparison from a few man months with the right people and the right input. Of course, this is the objective of the present study. There was agreement that

10 the sum of the capital plus operating costs are expected to be lower for the SC linac.

Flexibility in Operation to Vary Final Energy

We considered the potential advantages of the SC linac associated with increased flexibility in operation. It was pointed out that, unlike many research applications of accelerators, the APT application does not really require a fixed final energy, but over a large final energy range requires an approximately fixed beam power, corresponding to a fixed product of final energy times current Consequently, if the dc injector and low-beta section of the linac perform better at less than the design current, it would be an advantage if the linac could operate at that lower current, and still achieve the required beam power by increasing the final energy. The RT design, because of the cell geometry that is closely tailored to a specific velocity profile, has a nearly fixed final energy, independent of the accelerating field. This is because raising the accelerating field has the effect of shifting the synchronous phase, leading to a new synchronous particle, such that the synchronous energy gain and the final energy are nearly invariant. Even more important, the accelerating field of a CW RT cavity is not easily raised beyond a couple megavolts per meter, without increasing several potential problems such as a rapidly increasing rf power, additional cooling requirements from increasing rf wall-power dissipation, and in some cases, rf electric-breakdown concerns. Thus, even if the RT linac was designed for maximum flexibility like the SC linac with short independently-phased cavities, increasing the accelerating fields beyond a couple MV/m may be not be a very practical option for the RT case. For CW SC cavities, designed for accelerating fields near about 4-5 MV/m, modest increases of these fields, up to perhaps Ea = 7 MV/m are more easily obtained without the typical CW RT problems. Because of the independent phasing of SC cavities, the small number of cells with a broad velocity acceptance,' and the ability to raise the fields without deleterious performance impacts, the SC linac has no strict limitation on final energy. This extra degree of freedom to vary the final energy provides the SC design with the flexibility to change the final energy by raising the accelerating field, as long as the field or the input couplers are not limiting. The importance of having this energy-variability flexibility is not easy to quantify, but would provide another upgrade possibility to be described later, as well as the flexibility advantage just mentioned.

1 1 Larger Beam Aperture Additional design flexibility for reducing beam losses and possible HOM effects is provided by the possibility of having a larger beam aperture for the SC case. As is well known, the penalty of increased rf wall-power dissipation with increasing aperture radius makes large apertures an unattractive choice for the RT case. It is generally believed that this should be a clear advantage for the SC case. However, there was at least one' dissenting voice in the discussion, who raised the concern that the focusing might be necessarily constrained to be too weak to take advantage of the larger aperture. Thus, most in the group concluded that larger aperture has a very high probability of being an advantage for the SC case, but it has not yet been conclusively demonstrated to the satisfaction of everyone.

Reliability and Availability .

The reliability and availability for the RT and SC linacs, show no proven difference at present Some have argued that the SC linac has additional cryogenic and superconducting systems, and more cavities that may hurt the reliability. However, there are also fewer rf modules for the- SC system. The overall reliability also depends in detail on how robust the linac is to the various failure modes. No one was able to present persuasive evidence that either system has a demonstrated reliability advantage, after having been fully commissioned. Typical availability numbers at LAMPF are in the 85% range and have gone as high as 90%. As more CEBAF operational experience is gained, we will have better numbers for a SC linac. At present, CEBAF, partially commissioned, reached 69% availability during the first beam delivery, and CEBAF expects to reach 85% over a three-year period, a number that is comparable with LAMPF. From these numbers, one cannot persuasively argue for a significant reliability difference between the RT and SC technologies.

Upgrading Without Adding New Linac Structure

It was suggested that the SC linac may offer another option allowing an upgrade within the same structure to more beam power at fixed beam current, if higher accelerating fields and higher coupler powers can be achieved; this would allow higher final energy for the same linac structure. This follows from the arguments given previously that the final energy of the SC linac can be increased by raising the accelerating field. One might estimate that this approach might allow

12 an energy increase of up to as-'much as about 30%. Thus, the SC linac may offer important flexibility, both for ordinary operation and for upgrades of the machine.

Improved Longitudinal Dynamics

Finally, it was suggested that higher accelerating gradient in the SC linac may produce direct benefits from reduced beam losses as a result of stronger longitudinal focusing. This suggestion should be investigated through beam-dynamics simulation studies.

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if Power / Coupler (kW) 125 125 125 250 250 400 J so Power Source Klystrode Klystron Klystron Klystron Klystron Klystron Power/ Source (kW) 125 250 500 500 1000 800 ISO No. of Couplers / Source 1 2 4 2 4 2 i £ Cost of if Power ($/W) 4.66 2.94 2.25 2.03 1.57 1.65 4-.C6 AC-to-rf Efficiency 0.700 0.585 0.585 0.585 0.585 0.585 0.7<*o Total rf Power (MW) 86.76 86.76 86.76 87.26 87.26 87.61 t7.SO Tolal No. of Power Sources 558 279 140 175 88 129 If© Tolal Length (in) 756 756 756 594 594 540 Dissipated Power (kW) 5.41 5.41 5.41 5.83 5.83 6.14 7.7* Cryogenic Power (kW) 10.39 10.39 10.39 9.96 9.96 9.98 K1I HOM-Power Dissip. (kW) 1.83 1.83 1.83 1.66 1.66 1.58 M7 Tolal AC Power (MW) 127 151 151 152 152 152 fltf* Operation Cost / Year (M$) 47 56 56 56 56 57 4^ Capital Cost (M$) 697 552 492 418 378 367 40 Years Op.+ Capital (B$) 2.58 2.80 2.74 2.68 2.64 2.64 i.So

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if Power / Coupler (kW) 125 125 125 250 250 400 J SO Power Source Klystrode Klystron Klystron Klystron Klystron Klystron Power / Source (kW) 125 250 500 500 1000 800 No. of Couplers / Source 1 2 4 2 4 2 Cost of rf Power ($/W) 4.66 2.94 2.25 2.03 1.57 1.65 4-66 AC-lo-rf Efficiency 0.700 0.585 0.585 0.585 0.585 • 0.585 Total rf Power (MW) 86.76 86.76 86.76 87.26 87.26 87.61 Total No. of Power Sources 558 279 140 175 88 129 Sfo Total Length (in) 756 756 756 594 594. 540 Dissipated Power (kW) 5.41 5.41 5.41 5.83 5.83; 6.M 7.7f Cryogenic Power (kW) 10.39 10.39 10.39 9.96 9.96 9.98 HOM-Power Dissip. (kW) 1.83 1.83 1.83 1,66 1.66 1.58 Total AC Power (MW) 127 151 151 te 152 152 lid* Operalion Cost / Year (M$) 47 56 56; 56 56 57 Capital Cost (M$) 697 552 492 418 378 367 40 Years Op.+ Capital (B$) 2.58 2.80 2.74 2:68 2.64 2.64 5 ,4 JA/\ ^ ?d

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ftr CM ttSttA IK Mr HK ? ,1 _ Linac Architecture Issues 6A t«y • Beam beta varies from .4? to .9+ • Selected cavity parameters. * • Design logic. • Period layout. • Reference Design 400 kW couplers. Variations because of non-constant betas • Cavity cells change length. • EOT/Epeak ratio strong function of beta. • Cavity spare question. • Cost requires minimum number of cell lengths.

•) Linac Parameters • 100+ Mega Watts on target for goal require• ments. • Copper design used 0.1 Amp per channel. • Simple relative cost estimate shows insensitive cost minimum in 1200 MeV range. t 100 MeV (beta=.428) min level for elliptical cavities ?? Cavity parameters • 16.8 Mev/m average CEB AF peak surface field. • 6 cells per cavity gives reasonable size cavities at 700 MHz. • Power coupler limit 200 to 400 kWatts ??

4 Linac generating logic 1. Calculate EOT(in) from peak field at beta(in). 2. Select number of cells per cavity from EOT(in), coupler power Hmit, and beta(in) less than or equal to maximum number of cells. 3. Calculate beta(design) from the limit table ra• tio of beta(lower)/beta(design) for this num• ber of cells per cavity. 4. Calculate beta(upper) from the Hmit table ra• tio of beta(upper)/beta(design) for this num• ber of cells per cavity. 5. Select EOT (use) from the smaller of EOT(beta(design)) or EOT for coupler power limit at selected number of cells per cavity. . 6. Decoupling length is either 32 cm or for the 90 degree common RF supply, odd number of beta(design) lambda/4 greater than 32 cm + beta(design) lambda/2.

5 7.. Energy gain in a period is calculated with ap• proximate constant beta attenuation formu• las. 8. For the next period, a new beta(design) is calculated when beta(in) becomes larger than beta(upper). 9. To maintain smooth real estate gradient, pe• riod length is not shortened as number of cells per cavity is reduced. period length at 100 MeV 479 cm

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freq 200 400 600 800 1000 1200 700 Energy (MeV) (MHz) Reference Design 400 kW couplers

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Page 16 Cavity-Design for APTS CRF by Frank L. Krawczyk, LANL, AOT-1

1. Overview of Design Criteria

• We assumed ellipticaly shaped cavities for the whole energy range from 100 MeV to 1200 MeV. • Three representative energies at 100, 650 and 1200 MeV have been picked. • The shape descriptions are derived from work done by George Swain for PILAC and the LAMPF "afterburner": — Elliptically shaped noses — Straight section as side-wall (can be short) — Circular dome This setup has been shown to be best in terms of peak surface fields. • For each energy a reasonable inclination for the straight section has to be chosen: 3° @ 100 MeV, 7° @ 650 MeV and 10° @ 1200 MeV. A larger inclination is preferred by mechanical stability. It has been reduced for low and inter• mediate structure to reduce peak surface fields. • The nose shape (part of an ellipse with axis-ratio 2:1) has been used for additional optimization. The equatorial cavity- radius has been used for cavity tuning. The optimization criteria were: — Low peak surface fields — Mechanical/contruction constraints • The cell aperture has been fixed to 5 cm. This is the chosen beam pipe radius for our point-design. • The feasibility has to be demonstrated, especially for the 100 MeV structure (mechanical stability (D. Schrage), mul- tipactoring).

2. Some Data Describing the Cavities

ZT2 (U\ " Epk E (MeV) maj. ell. T 0. W k(%) EOT EOT

100 6 cm 0.78151 180.43 2.305 3.416 5168.2 MV 650 8 cm 0.76876 533.31 1.78 1.78 2813.9 &

1200 8 cm 0.76494 583.35 0.904 1.61 2682.8 MV 7.576 in 19.242 cm

2.700 in 6.858 cm R

1.57 in 4.00 cm 7.441 in 3.15 in 18.900 cm 8.00 cm

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.+ E -> 3. Coupling Considerations for APTSCRP Cavities

Coupling between cells ajid_cavities is an important issue for several reasons:

• An effective use of coupler power at low energy favours 6 to 8 cell cavities. This favours larger cell-to-cell irises. • Iris coupling of input power determines a mmimum pipe- size. C ix.c>

All these influences motivate the investigation of coupling as a function of cavity geometry.

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O.l + + f t too few ^w '6e>° te°° £1 £/UfJ • The comparison of recpiired to achievable coupling indicates that above 100 MeV and-bekw*65Q-Mq¥ multi-cell cavities will require a cell-to-cell iris size larger than the beam-pipe bore radius. When we have a confirmed analytic/numeric model on the coupling - field-tilt relation additional design work will be done to find the necessary multi-cell iris size. • This work will also require the knowledge of the number (6-9) and values of the different /?'s to be picked along the accelerator. 4. On the Choice of Peak-surface Field and Gradient In the baseline design we tried to combine several criteria for the the choice of rf-acceleration at any point in the linac. « • • Choice of the highest possible gradient in each cell. The limit for this gradient is determined by the corresponding

peak surface electric field at this j3 (from Epk/EoT). • The achievable gradient then determines the number of cells chosen at this energy. Enough cells are chosen to make use of as much of the design input-power as possible. The electric peak surface field chosen in our design as maximum tolerable field level is 16.7 MV/m. This number corresponds to the level found tolerable for basically all cavities at CEBAF. To judge this choice a closer into the world-data of achieved peak-surface fields in superconducting cavities is necessary. Padamsee/Weingarten[l,2] developed a heuristic description for the number of emitter-sites S(E) per sq cm in superconducting cavities. (This formula yields emitter densities that correspond to one emitter-site per cavity).

S{E)[-\] = 3.17 x l(T50/i? x S(100MV/m). (1)

E has to be specified in MV/m and S(100MV/m) is 0.15cm"2. The corresponding curve lies in the lowest part of the measure• ments. 0 Under the assumption of a higher "tolerable" number of emitter- sites peak surface fields for a given cavity surface can be de• termined in a less conservative way Such higher numbers of emitter-sites N can be chosen to still reasonably approximate the world-data of Epeak over surface area (See Figure). N(= S(E) x A) =.3.17 x W~5°/E x 0.15cm"2 x A, (2) where A is the surface area of the cavity in cm~2. From this the surface peak electric field can be derived:

E[MV/m] = log{N!{Z.n x 0.15cm-2 x A) (3)

These curves indicate that for most of the accelerator this field limit is appropriate. • At 1.2 GeV, a 3-cell cavity at 700 MHz approximately has the same area as'the CEBAF multi-cell cavity at 1500 MHz • At 100 MeV a 6-cell cavity at 700 MHz approximately has an area of twice the CEBAF cavity value. For the portion of the accelerator with this high number of cells the peak surface fieldmigh t have to be reduced a little bit. Since the curves are fairly flat for higher surface areas, the reduction can be expected to be minor.

i\- world data, peak electric field versus surface area

• Wuppertal • Cornell A Saclay XCEBAF XCERN/DESY • LANL A LANL points

surface area (m"2) Los Alamos NATIONAL LABORATORY Accelerator Operations & Technology Division

PRELIMINARY * STRUCTURAL CONSIDERATIONS for ELLIPTICAL CAVITIES

• FABRICATION CONSTRAINTS

• COLLAPSE UNDER VACUUM

• FREQUENCY SHIFTS

• STRUCTURAL RESONANCES

R. Gentzlinger D. Schrage E. Swensen

APT SC WORKSHOP May 1995 Los Alamos NATIONAL LABORATORY Accelerator Operations & Technology Division

NIOBIUM PROPERTIES: * PROPERTY NIOBIUM COPPER SS303 Density g/icm3 8.66 8.94 8.00 Melting Point °C 2468. 1083. 1400. Modulus of Elasticity 99. 115. 207. GPascal Poisson's Ratio 0.38 0.33 0.31 RRR 250. 70. 1. COST $/kg 75. 2. 0.5 Yield Strength @300°K 48. 48. 193. MPascal Yield Strength @300°K 425. -70. 570. MPascal Therm Cond @300°K 52. 391. 16. W/Meter °K Therm Cond @4°K 50. . 500. 16. W/Meter °K Thermal Expansion -0.15% -0.32 % -0.20 % 300 - 4 °K

NIOBIUM IS NOT AS WELL CHARACTERIZED AS COPPER

AND STEELS (k & ay data @4 °K are from Kneisel & Rao)

HIGH PURITY & HEAT TREATMENT AFFECT GRAIN SIZE WHICH AFFECTS YIELD STRENGTH

APT SC WORKSHOP » M Los Alamos NATIONAL LABORATORY Accelerator Operations & Technology Division

FABRICATION CONSTRAINTS:

• "CONVENTIONAL" FORMED HALF-CELLS WELDED FROM THE OUTSIDE (cosmetic underbead) • MATERIAL THICKNESS ~ l/8th inch - COMPROMISE AMONG THERMAI/FORMING/MECHANICAL RESONANCE CONSIDERATIONS • MUST WITHSTAND VACUUM LOAD AT AMBIENT TEMPERATURE

APT SC WORKSHOP May 1995 Los Alamos NATIONAL LABORATORY Accelerator Operations & Technology Division

CAVITY DESIGN RULES:

. BEAM PIPE RADIUS: 5.0 cm . NO HEAT TREATMENT, RRR -250 • HELICOFLEX VACUUM SEALS on Nb ALLOY FLANGES • MINIMUM 3° CAVITY WALL SLOPE TO ALLOW FLUID DRAIN . MUST WITHSTAND VACUUM LOAD @ 300°K . LOCAL YIELDING PERMITTED BUT von-MISES STRESS SHOULD NOT EXCEED 5000 #/in2

APT SC WORKSHOP Los Alamos NATIONAL LABORATORY Accelerator Operations & Technology Division

FIALF-CELL STRUCTURAL BEHAVIOR @ 100 MeV (p = 0.43) CASE# IRIS STIFF. PRESS. MAX MAX FREQ. NOTES RADIUS AXIAL von-MISES SHIFT DEFLECT STRESS inch #/in2 inch #/in2 MHz 01 Free None N/A 0.000758 N/A -0.278 0 02 Free None 14.7 -0.069500 17518 -8.410 03 Free None 0.0 -0.007760 2202 -0.997 1 04 Fixed None 14.7 -0.011600 13592 0.120 05 Fixed 4.58 14.7 -0.001500 3984 - 0.027 06 Fixed 4.58 0.0 -0.002260 1717 i -0.261 1 07 Fixed • 4.58 14.7 -0.002570 4396 -0.239 1

Notes: 0. Uniform Temperature Increase of 100°F 1.100# Axial Force @ Iris for Tuning

APT SC WORKSHOP May 1995 Los Alamos NATIONAL LABORATORY Engineering Sciences A Applications Division

NATURAL FREQUENCIES OF THE RF SUPERCONDUCTING CAVITIES

UNSTIFFENED CAVITY STIFFENED CAVITY FREQUENCY (Hz) MODE FREQUENCY (Hz) MODE 1 8.6 Transverse 19.3 Transverse 2 8.6 Transverse 19.3 Transverse 3 15.6 Transverse 34.6 Axial / V 4 15.6 Transverse 36.5 Transverse •• • 5 19 Axial 36.5 Transverse > . 1 ~ € ~ 36.2 Transverse 70.2 Axial 1 7 36.2 Transverse 82.6 Transverse W ITH 8 39.4 Axiai 82.6 Transverse 9 43.3 Transverse 102.1 Transverse 10 . 43.3 Transverse 102.1 Transverse

APT SC WORKSHOP May 1995 *

Los Alamos NATIONAL LABORATORY Accelerator Operations & Technology Division

CONCLUSIONS: • STIFFENERS WILL BE REQUIRED TO WITHSTAND VACUUM LOAD AT AMBIENT TEMPERATURE - THESE ARE SIMPLE • STRUCTURAL PERFORMANCE AT 4°K IS NOT A CONCERN • FREQUENCY TUNING FORCES ARE NOT EXCESSIVE: 10# TO NULL PRESSURE FREQUENCY SHIFT OF STIFFENED CAVITY • MORE WORK ON STIFFENERS WILL BE REQUIRED TO INCREASE STRUCTURAL RESONANT FREQUENCIES AND TO DEFINE THE REQUIREMENTS

APT SC WORKSHOP Mav 1995 r SUPERCONDUCTING RF CAVITY OPERATION AT CEBAF

Andrew Hutton

CEBAF

Santa Fe, May 8-11,1995

The Continuous Electron Beam Accelerator Facility an*4AndWifcW«ifcCoi*«noatI Santo Fa Talc May8-11,1995

m*vr*i*m*nm^ MACHINE CONFIGURATION

45-MeV Injector ^ (2 1/4 Cryomodules) y^

End<^ Stations M

• SRF Acceleration System

• 338 cavities In 42 1/4 cryomodules, Installed and functional

• Exceeds G, Q specification twofold

• Operating experience

• Beam-induced microphonics were observed, takes cavity out of phase lock • Varying the beam repetition rate modifies which cavities have problems • Operation with superfluid helium has eliminated this effect

• Helium temperature changes affect the tuning ) • Keeping all of the cavities in tune requires automated software • This effect limits recovery time from (infrequent) CHL crashes

• Extremely few interventions required in the tunnel

The Continuous Electron Beam Accelerator Facility amhJAndrtw'a Work, Confanmcat] 8«nt« Fa TaJk May &-11.1995 The Continuous Electron Beam Accelerator Facility E and Q at field emission onset for 33.8 cavities

Mean: 8.7 MV/m @ Q*8.5 x 10* Best :18.5 MV/m @ Q=7.7 x 10s

6 8 10 12

£acc[FE onset] (MV/m) Problems Requiring Access to Machine by WBS 1 Personnel (May, 1994-May, 1995)

• Cleaning of two field probe connectors (This problem was a result of excess humidity in tunnel, and should no longer be a problem.)

• Diagnosis and /or replacement of eight stepper motors. (Only two motors were found to be problems -excess humidity again.) (Other six turned out to be controls problems.)

• Changes to arc detector hardware (Access to machine required on three occasions). This should be viewed as a systems integration issue, rather than a maintenance issue. .

• Reconnect vaccuum valve cables on one occasion.

• Leak checking required in S. Linac as a result of beam strike on valve. (Access required for three days.)

• Diagnosis and /or repair of two IR detectors.

• Wrapping of waveguide with copper tape on three occasions. (This was done to protect IR detectors from RF leakage.)

Provided by MDnuy CEBAF-SRF r APT OPERATIONAL ISSUES — RELEVANT CEBAF EXPIRliNCE (An^ \kH>„) • Long term performance issues

No degradation in performance seen after 1-3 years running

• Possible changes in niobium if beam hits it

No information

• Quench protection - need it No indication that CEBAFhas ever had a real quench during operation Quench protection trips occasionally for other reasons

• Stray fields from focusing magnets

Never seen any indication that this could be a prdblem

• Robustness of linac if cavities are down

No different from a copper linac

The Continuous Electron Beam Accelerator Facility ' arnhJArHirew's Wo*. Conference^ Santa Fe Talk May 8 -11,1995 APT OPERATIONAL ISSUES (cont) r RELEVANT CEBAF EXPEDIENCE • Reliability and Availability

Start every run with a 5-10% overhead to maintain up time The majority of problems are related to RF, not cavities

• Spare module for each section

CEBAF has not needed this, but one spare cryomodule is in the plan

• Do you need fast acting valves at each end of each cryostat CEBAF has this, useful for isolation, never needed for real vacuum accident

• What if you lose a cavity

LEM, autosteerand continue (10 minute interruption) This is vital in any linac if beam properties are important APT may not require it

——— ! Ill * The Continuous ^inctron Beam Accelerator Facility arnhJAndraw's Worfc, Conferences! Santa Fe Talk Mny 8-11.1995 APT OPIRATIONAL ISSUES (cont) r RELEVANT CEBAF EXPERIENCE • Phase and amplitude control Important for reproducibility, not more Stringent than copper RF system Important for stability if beam properties are important CEBAF uses automated software routines to back up hardware.

V • Coupler performance degradation with beam

Not seen any indication of this effect in CEBAF Main worry at CEBAF is the cavity window (APT is same)

• What overall reliability can we expect ; .

CEBAF, partially commissioned, reached 69% during first beam delivery CEBAF expects to reach 85% over a three year period This is better than other copper linacs of comparable complexity

The Continuous Electron Beam Accelerator Facility amhJAndrew's Work. Conference*) Santa Fe Talk Mny 8-11,1995 ^SRF CAVITY LIMITATIONS-

• SRF Cavity gradient is limited by several different effects

• Field emission

• Initially, limit was set at 1 watt of field emission

• About 20% of the cavities had to be lowered below this by 0.5 - 1 MeV/m • Depending on location, field emission can cause arcs on windows

• Inconclusive evidence that field emission can be beam current related

• Quench }

• Limit was set at 1 MeV below quench onset

• There has never been a quench of a cavity during operations • It would not be a major problem if we had one • Worst case scenario is a cold compressor trip - no damage

ThZcTnfiuous Electron Beam Accelerator Facility amrHAndr.w'e Work, Conferences] Santa Fa Talk MayW1,1995 SRF CAVITY LIMITATIONS (cont.)

Waveguide arcing

• Caused by • Reflected power (usually beam related) • Field emission near cavity window • Field emission in adjacent cavities

• False trip»s were caused by • Beam loss on arc trip detectors (photomultiplier tube) • Solved by putting integrator on detector • Requires trip condition to last longer than tune-up beam pulse

Waveguide arcs (real and false) have been the major source of beam trips

The Continuous Electron Beam Accelerator Facility •mhtAndmW. wortc. Coofti»nc«t) Santa F« T«* M«y 8-11.1995 SRF CAVITY LIMITATIONS (cont.)

Increase in waveguide vacuum

• Usually associated with waveguide arcs

• Used a posteriori to differentiate real from false waveguide arc trips

RF Power limitations

• Currently RF power limited to 1.5 kW • Lowest tap on power transformer • Resulted in power savings of $500k last year, more this year • Dramatically reduced klystron failure rate

• Klystron drive power limits maximum gradient to 9 MeV/m

The Continuous Electron Beam Accelerator Facility «mh{AndreWt Work, Conference! Santa Fe Talk May 8-11,1995 SRF CAVITY COMMISSIONING PERFORMANCE VS. POSITION IN THE CEBAF ACCELERATOR (5 kW RF, NO BEAM)

i i | i i i i 100 150 200 250 300 CAVITY POSITION IN THE CEBAF ACCELERATOR CEBAF/SRF/TJP/12/14/94- CHL OPERATING EXPERIENCE

• Availability Availability - 96.5%

Cold Compressors Longest Run without trips 35 Days Average run between trips 10 days Normal restore time < 4 hours Fastest restore time 1 hour 30 minutes Cold compressor restarts are fully automated

The Continuous Electron Beam Accelerator Facility amh[Androw*8 Wotk, Conferenca*] Santa Fe Talk May 8-11.1995 TRANSFER LINE PRESSURE AS A FUNCTION OF TIME

Trip 10:20 am 0.02 Restart begun llj:40 am

0.01 Stable operation. 14:10 pm

0 SUCTION 81//Q4/'95 10:30 11:03 11:30 12:00 12:30 13:00 13:30 14:00 ' 14:30 B1^B4^95 HilfrMiHi CRYOGENICS DOWNTIME JUN 94 - MAR 95

Hr 80

60

AVAILABILITY 40 96.5 %

20

ifelL 0 %m JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR

4 K SYSTEM 2 K SYSTEM CRYO CONTROLS RF SYSTEM • One klystron per cavity, one High Power Amplifier (HPA) per cryomodule • Operating frequency 1497 MHz • 340 klystrons in 43 HP As • 344 low level control modules • Includes amplifiers for "warm" injector cavities • Master oscillator and distribution

• Operating experience • Low level control loops functioning well • Being tuned for optimum stability under commissioning conditions • High level control software functioning well • Being augmented daily

Software control of RF was a major factor in commissioning success

The Continuous Electron Beam Accelerator Facility . amh{Andn>W. Wock. Confewocaa] Santa Fe Talk ' May ft-ll,iM5 RF SYSTEM (cont.)

• Phase distribution has been a major problem

. • Temperature compensation not yet activated • Operation in hot and cold weather difficult

• Observed thermal drifts and phase jumps of up to 30°

• Currently completing installation of system upgrades • Laser reference system • Temperature stabilization of RF drive line components

This has been one of two major causes of beam tuning time

• r^r^tSOSttti tgagg^tg/fjgtmmmmmmmmUMmmmmmmm , .t.^-.-mnnv^f^fv ^•*-j^ni^jM«F«

Operation of the linacs requires sophisticated high-level software

• Automated Cavity Tuning (Autotune) • Burst i • Sweep

• Autotrack

• Linac Autophasing

• Linac Energy Management

The Continuous Electron Beam Accelerator Facility amhlAndrew** Work, Conferences] Santa Fe Talk May 8-11.1995 r AUTOMATED CAVITY TUNING

Purpose: Automated measurement of cavity resonance frequency and tuning of cavities to the operating frequency. I-. • Cavity tuning procedure is accomplished in three steps:

I 1) Burst Mod6 (Rough tuning)

Cavity resonant frequency f0 is measured by driving the cavity with a noise spectrum.

Phase of incident signal is modulated with a bandwidth-limited (± 5 kHz) psuedo-random signal.

f0 can be determined within ± 50 Hz from the response signal of the field probe

6 which has a narrow frequency spectrum (QL = 6.6 x 10 ).

Stepper motors bring cavity into tune within 100 Hz

TrZ^niirZousElectron Beam Accelerator Facility amhfAndreWa Work, Conferences] San,. Fe Talk May 8-11.1995 AUTOMATED CAVITY TUNING (cont'd.)

2) Sweep Mode (Exact tuning)

Single-sideband modulation is applied to the carrier while sweeping the modulation frequency over a range of ± 200 Hz in steps of 5 Hz.

The measured de-tuning angle *F as a function of modulating frequency is compared to the predicted curve to determine the resonance frequency

\|/ = atan- 2Q Vf + Vo Lfo as well as the phase offset.

3) Autotrack (locks cavity on frequency)

Uses the phase offset *F0 determined above to keep the cavity tuned to the operating frequency

rTe^nUnuousElectron Beam Accelerator Facility amhtAndr^. Wo* Confer***.] Sanf Fe Talk May8-11.1995 LINAC AUTO-PHASING

Purpose: Precise cavity phasing is achieved by maximizing the linac energy.

Phase of an individual cavity is changed by ±30°. • Initial beam position and beam position changes are recorded.

Crest phase is found from

y -y- . t=(t>S+atani + >tan-^ crcs 2 fc (y++y--2y0)

<|>0: initial phase setting, y0: beam position at $0, y±: beam position at <|> = $0 ± Aty

Reproducibility better than 1°, Phasing time 2 min/cavity

^ — • • • c^snn, «nh[AndreW«Wofk,ConferencwJ Santa F8 Talk May S-11,1995 The Continuous Electron Beam Accelerator Facility LINAC AUTO-PHASING (cont.)

A recent improvement uses the energy feedback system

• The phase of a cavity is changed by ±30°

• The energy feedback system restores the linac energy to nominal

• The change in the feedback control variable measures the energy change

• Advantages

• Linac can be phased during operation (4 hour per linac)

• Status

• Operational now including faster cryomodule-by-cryomodule phasing

• Exception handling being incorporated

iZ~~ousElectron Beam Accelerator Facility .mhtAnd™'. Woric. Confer***.] Santa Fe Talk Ntay 8-11.1905 LINAC ENERGY MANAGEMENT (LEM)

For a given energy at the end of North or South Linac and available cavities:

• Optimizes the cavity gradient distribution using individual cavity characteristics \ • Includes the option of balancing cavity gradients

• Calculates energy profile along the linacs

• Calculates linac quad values consistent with calculated energy profile for different FODO cells: 60°, 90°, 120°

• Down-loads and sets RF and Quads (including hysteresis)

(based on a SLAC program developed for SLC)

TheCwuZoWaectron Beam Accelerator Facility .mhtAndreW. Work. Conference] S«nt« Fe Talk Maya-1U995 •it

SRF CAVITY OPERATING FIELD VALUES AND LIMITS VS. POSITION IN THE CEBAF ACCELERATOR, (12/12/94,1.5 kW RF) y ! 14-

itf

•I

•: ! i . r~. r-ap>- 100 , 150 200 250 CAVITY IN THE.CEBAF ACCELERATOR CEBAF/SRF/TJP/12/14/94 M$sM&&&

ACCELERATOR, PRODUCTION

Cavities developed al Cornell ann CEBA* and produced hv indusu \\ ' '

Pairs assembled and tested, at CKBAI

AVI !

Cfvounits fabricated al CEBAI'

.WW. .... > 1—1 ^^ 1—1gjiig§ | Production cryomodules assembled 61§$»2 H dtjwwMfe v__J tested, and installed m tunnel < Sg^r *ww ru < u> oviniu f ^LINAC ENERGY MANAGEMENT (cont.)- ,

• Required input

• Maximum gradient permitted for each cavity • Usually, the minimum of all of the SRF and RF limits

• List of available cavities • Integrated into the maintenance log • Individual cavities and integral information are tracked for analysis • Most useful number - energy overhead available (usually 6 -10%)

• Set-up requires

• Matching calculated linac energy to arc energy setting

• Apply a "fudge factor" to get match • Usual value of "fudge factor" 1.01 - 1.05

^CESAr The Continuous Electron Beam Accelerator Facility arnhTAndrew'. Wo* Conferences] Santa Fe Talk May 8-11.1995 CW CURRENT ACHIEVEMENTS

Maximum current achieved in North Linac 110 jiA CW • Specification 200 |iA CW per pass, 1 mA total

• Current limited by time available for tune-up of beam-loss monitors • 200 jxA CW beam transported to 45 MeV beam dump in the Injector • Gun has produced currents of 340 ^iA

The Continuous Electron Beam Accelerator Facility amhjAndrew's Work, Conferences] Santa Fe Talk May 8-11,1995 r COUPLED BEAMS

Beam coupling refers to a coupling between horizontal and vertical oscillations in the beam

Under normal (uncoupled) conditions, the horizontal and vertical motions of the beam are independent

When the beams are coupled, an oscillation in one plane coupler into the other plane, like two coupled oscillators

This can lead to an apparent increase in the beam omittance

• Note that Louiville's theorem says that phase space (omittance) is conserved, so the increase is only apparent - but very real!

The Continuous Electron Beam Accelerator Facility amhr.Artdrew'8 Work, Conferences] Santa Fe Talk May &-11.1995 UNCOUPLED EMITTANCES

in the absence of coupling, the product of the projections of the phase space area on the X and X' axes is a constant

S3AJMS!ISS>?& ~*>® C&tt&att&as. lEt'&c&oct &esm Acc-eieesiice Fatcc&iY amifo{f&n>iarew":s WcoSgs CoopAmp TFate COUPLED EMITTANCES

in the presence of coupling, the product of the projections of the phase space area on the X and X' axes is a never a constant and is usually much larger than when uncoupled J

T an&fAa&evfs Y/wfc> CcjpSnp TaUx. }3Api»i?35 he Continuous £t'ec(ron Beam Accelerator Facility

TYPES OF EMITTANCE INCREASE • Filamentation

RF focusing In circular machines causes particles of different energies to rotate around the RF bucket at different speeds. This can cause an effect like an egg beater resulting in real emittance dilution. ! This effect is not relevant for CEBAF or APT

• Longitudinal variation of Emittance

If the front of the beam is not in the same position as the back of the beam, the projection of the beam on a screen is apparently enlarged (think of the beam as a banana - the projection is thicker than the cross-section of the banana). This effect is seen often in SLC du

• Emittance Projection

If the beam is strongly X-Y coupled, the projections of the phase space onto the visible axes X, X\ Y, Y' can all be increased -

M r- This is a realproMem M CEBAF, m.av be problem for APT

TTe ^niimJousElectron Beam Accelerator Facility amhlAndrew's Wbrtc Conferences] Santa Fe Talk May 8-11.1995 MAIN CAUSE OF COUPLING • Produced by skewfields in the SRF cavities due to asymmetry in the HOM couplers

• Corrected by installing 50 air-cored skew quadrupoles around the BPMs in the Linacs which a're next to the SRF cavities ; Problem for CEBAF, probably not for APT

Other causes

• Point Coupling in the Linacs

Produced by mis-steered beams or mis-phased cavities * Problem for CEBAF and APT

• Mis-steered beams in the linacs producing large offsets in the SRF cavities Need to learn how to steer higher-pass beams cleanly out of the recombiners into the linac and into the spreaders r Problem for CEBAF, not for APT

The Continuous Electron Beam Accelerator Facility amhfAndrew's Work, Conferences] Santa Fe Talk May 8-11,1995 SUMMARY

CEBAF operates with over 300 SRF cavities

Availability of SRF cavities have never impacted commissioning

• Most problems are with RF drive

• Solution is to take cavity off-line and LEM to restore energy profile

To improve availability, prefer >5% spare accelerating gradient

• Experience at SLC with copper cavities is similar

Only problem caused by superconducting cavities - coupling

• Should be avoided in next-generation design

• Effect is specific to a multipass linac

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Cryostat Candidate Design Cs^ <•, 6*«t*(yen) "CERN Like11 Design (Some Modifications) a) 2 Outer Skins (Original CERN Design had 1 Continuous Skin) b) Small Access Panels c) Upper & Lower Fixed Longerons 1. Upper (He Feed and Return Lines, Electrical Feed Thrus) 2. Lower (RF Feed Thrus, Vacuum Pumps, Diagnostics) Modular Design a) Vacuum Vessels can be Bolted Together b) End Domes at Warm to Cold Transitions 4 RF Cavities Housed in One Vacuum Vessel Assembly

APT SC WORKSHOP May 1995 Los Alamos NATIONAL LABORATORY Engineering Sciences & Applications Division Cryostat Candidate Design • Thermal Radiation Shield a) Self-Supporting Piping Frame b) Uses Evaporated Gas from the Liquid He Bath c) .020 Copper Sheets Mechanically Clamped to Frame (Access Requirement) d) 40 Layers of Superinsulation

• Cavity is Suspended at each end of Vessel by 2 Low Thermal Conductive Support Rods, An Addition Rod (Not Shown) is Used to Fix the Cavity Longitudinal Position at the RF Drive Line • Magnetic Shield Still to be Incorporated • A Cavity Assembly Consists of The Cavity, He Tank, Tuning System, Thermal Shield & maybe the Magnetic Shield?

APT SC WORKSHOP May 1995 Los Alamos NATIONAL LABORATORY Engineering Sciences & Applications Division Cryomodule Los Alamos NATIONAL UBORATORY Engineering Sciences & Applications Division Subcryomodule Assembly (Front View)

STIFFENING RING

HELIUM1- TANK BELLOWS (2 PLACES) VACUUM VESSEL INTERFACE FLANGE

TUNING ARC VACUUM VESSEL OUTER SKIN

BELLOWS

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PICK-UP PROBE

HE TANK APT SC WORKSHOP May 1995 Los Alamos NATIONAL LABORATORY Engineering Sciences & Applications Division Subcryomodule Assembly (Top View) TUNING ROD

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APT SC WORKSHOP May 1995 Los Alamos NATIONAL LABORATORY Engineering Sciences & Applications Division

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APT SC WORKSHOP May 1995 Los Alamos NATIONAL LABORATORY Engineering Sciences & Applications Division

INNER RF Feed Line CONDUCTOR • Maximum Lateral Displacement of Center Conductor • Is Active Longitudinal Adjustment of Center Conductor Required? • Type of Cooling of Center Conductor? • Type of Cooling for Outer Conductor?

APT SC WORKSHOP May 1995 R&D Program (Wangler, 20 min) • What needs to be tested? What are the issues? • 1) Cavity development, 2) Coupler development, and 3) Integrated test capabilitv vyith beam are the three components that we have identified.

• Single cell tests. What (3 values? i • Multicell tes s. How many and what kind? What new issues are being addressed? • Need integrated test capability with beam for development of coupler/cavity system performance in realistic environment. How important is this? Possible Cavity Tests Without Beam

• Single cell tests at different [3 to address multipactina and mechanical issues. • Multicell tests to confirm 1) ability to achieve desired fields. and 2) tuning mechanisms for frequency and field uniformity. Integrated Test Capability With Beam

• Difficulty of finding a suitable beam to perform realistic high-p tests. Tes!s of high-p cavities at low p don't work since you cannot transfer much energy to beam if p « Pdesign. i Some Options Considered:

• Could you do a beam test with room temperature DTL cavity at 7 MeV, using 100 mA CW beam on the FED? • Could you do a superconducting beam test at 7 MeV (p = 0.13) on the FED using a multicell spoke cavity designed for p = 0.13? • How important is it to conduct integrated tests with an elliptical structure if an integrated test with the spoke structure has already been done?

• Could you do a superconducting beam test in 3PW2 mode at 40 MeV on the "ED for elliptical cavity designed for p = 0.8? • Can you do any meaningful tests with relativistic electron beam? • Can you do any meaningful tests wl*h LAMPF proton beam? Some Beam and System Questions That Could be Answered by Tests.

• Cavityvfecovery after breakdown when beam is present. Example: Can beam continue to excite cavity after cavity has quenched? • Effect of a dc magnetic field near the cavity on cavity recovery after breakdown (especially after quench?) •••i • Effects of beam-excited higher-order modes on beam, cavity, or input coupler? • Performance of cavity after a large accidental beam loss on cavity walls. • Do«5 *flw Pairftr QA<- Mtwut iv Hie beam TGS+III Coupler Perjor>ui0ic

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Cvhml peHcr level. COUPLERS AND RF WORKING GROUPS Summary of Sessions on Cavity Couplers and High-Power RF Systems for Super conducting APT Systems

Power System Architecture

The point design shall be 1.0 MW klystrons at a frequencyo f 700 MHz, the same as the room temperature machine. This power limit has been suggested by the klystron manufacturers, and it is only a modest extrapolation fromth e 1.2 MW powers available at 353 and 508 MHz. The power shall be split into 4 or 8 couplers, and the 4 coupler solution is expected to be less expensive, but have slightly more risk. There are two levels of 3 dB splitters, and 4 cavities are therefore driven by each klystron. Only one feedback loop is used with each klystron, and no active phase and amplitude control is used on the high power side of the generators. There will be mechanical length adjustments of the transmission lines as part of the commissioning process, but they will only be set and then left alone.

The backup generators are 250 or 500 kW klystrodes with 250 kW couplers. While we expect cost disadvantages, this system should be more robust and tolerant of failures.

The most conservative klystrode system is 125 kW, only twice the demonstrated output power of the television klystrodes, and less than half of the 300 kW CW power demonstrated at 267 MHz. This klystrode, together with a 125 kW coupler, makes a conservative, robust RF system, but the cost is probably prohibitive.

RF Controls

The RF control problems are expected to be similar to those of room temperature systems, because the loaded Q of the cavities will be only a factor of about two higher than the room temperature case (QiA2*10^), although the intrinsic Q will be very high

(QoA2*109). A single control loop is to be used with each klystron, and the cavity field sample is the appropriate summation of the samples from the four individual cavities in the cryomodule. The microphonics need to be looked.at, but are expected to be fairly small, due to the large loaded bandwidth of perhaps several kHz. The detuning with beam loading will have to be controlled by a tuning system that will probably be piezoelectric. The beam detuning will be about 2.8 kHz. The tuning system will be similar in principal to the system used for the Ground Test Accelerator, but the actuator and time response will be much different.

The phase and amplitude tolerances for the SC case need to be defined, both from the beam dynamics side, and the electrical engineering side, to findth e best compromise between robustness, practicality, and system cost. Without doing that analysis, 1% in amplitude and 1° in phase over a 100 kHz bandwidth are the nominal design parameters. The required tolerances may well be different than those we are used to for normal conducting accelerator systems. RF Costing Rules

The 700 MHz RF system will cost only a few cents per Watt more than a 350 MHz system. There was widespread agreement that the purchased systems will result in costs of from $1.50 to $2.50 per Watt When the cooling system, the buildings, the primary power, and the RF personnel are included, the RF system costs are then from $3 to $5 per Watt, and the answer is site dependent. Vendor estimates also tend to vary, depending on the vendor's work load and their design philosophy. A European circulator company, for example, estimated that two 0.5 MW circulators would cost O'times the cost of a 1.0 MW circulator at 700 MHz, CW. A Japanese circulator company sold KEK 4 250 kW circulators for the same cost that they estimated a 1.0 MW version would cost, at 508 MHz CW. There is also agreement that the bare components could be purchased very inexpensively, for about $1 per Watt, but then there is a monumental problem of making a system out of the components. The costs for the RF system for both the normal conducting and super conducting systems will be re-evaluated this Summer. There are some recent RF systems that were purchased, and their costs cannot be ignored. These systems are: 1) The Argonne Photon Source (APS) RF system is 5 1.0 MW transmitters at 350 MHz, CW, and the cost was about $3.40 per Watt, including the RF group, but excluding part of the cooling and control systems. 2) The CWDD RF system at Argonne cost about $5. per Watt for 2 1.1 MW systems at 353 MHz. This includes installation and some building modifications. 3) The CRNL' klystrode system cost $5.5 per Watt for the transmitter, power supplies, and tubes for 2 250 kW CW RF systems at 267 MHz.

The APS personnel feel that they were very lucky since their major suppliers needed business, so the prices were very low. Thus, they now believe that they could not assemble the systems so inexpensively again. The vendor on the CRNL klystrode RF system was about two years late on a fixed-price contract, and they lost much money. They also would not sell the same system except at a significantly higher price. Thus, the cost extrapolation to well over 110 MW of RF systems is very difficult.

Higher Order Modes

A rough calculation of the HOM losses indicates that about 10 W/cavity will go into the TMoi l mode, compared to 50 W at most for the RF losses. The sum of the other HOMs could well be of the same 10 W order, so an HOM coupler is required.

Input Power Coupler and Windows

The main choice is between a Cornell-style wave guide coupler, or the CERN style coaxial coupler. The consensus opinion is that the coaxial design is preferred, but the wave guide progress should be monitored as a backup. The major, disadvantages of the coaxial design is the extra complexity if it has to be biased to suppress multipactor, and the possibility of vibrations in the cantilevered center conductor. The major problems expected fromth e coupler is multipactoring, especially where the electric fieldsar e complex, such as near discontinuities. Careful design and analysis will be required. The number of couplers per 4- cell cavity was discussed. A single coupler per cavity is the most economical, but 250 kW would have to be transmitted at 100 mA of beam current, and this is beyond what has been demonstrated (with beam) to date. We are in favor of using two 125 kW couplers per 4-cell cavity, since this is within the present state of the art. This solution involves another level of splitting of the RF power, and more penetrations into the cryomodule, so the cost will be higher. We feel that the extra cost significantly lowers the project's risk, and also provides an easier upgrade capability to higher current: With this method, current of up to 200 mA should be possible in just a few years for a major upgrade of the APT system, should it be required. With two couplers per cavity, we can drive from alternate sides, and so minimize any perturbations on the beam caused by the drive point.

High power windows have been always operated at warm temperatures, so this is the baseline design. There are three practical arrangements: the planar wave guide window, the disk in coaxial window, and the cylindrical tube window. This last variant has the disadvantage of strongly varying fields in the ceramic. The coaxial disk window is used in ' all the klystrons at 1.2 MW CW, so this is the preferred technology. The planar wave guide window may cost less, and it is available fromsevera l vendors. It is wise to develop more than one typeo f window, and test each type.

Development for the RF Power Systems, Couplers, and Windows

The only items of concern are the klystron itself, and the power coupler. 1.2 MW CW klystrons exist at both 353 and 508 MHz, but the vendors have suggested that at 700 MHz, where the power densities are higher, we begin with a 1.0 MW klystron. One vendor suggested that their klystron would be lower riskwit h two output windows, but this seems to drive the system cost higher. The 700 MHz klystron should be robust and reliable, but we recommend that two vendors develop separate klystrons, so that APT can select the highest quality device. The downside of the klystron is that the operating efficiency will be about 58%, as compared to the 65% that it can deliver while saturated.

Thus the development of a klystrode, which could produce power at 70% operating efficiency, is very attractive. Smaller power supplies and smaller cooling systems could be used compared to the klystron case. The main question for the klystrode is the power level of the device, but at least one vendor claims to have methods of developing 1 MW klystrodes. With smaller generators, the system should be much more robust, but also more expensive.

Much simulation has to be done for the super conducting RF system. We have not started the difficult problems of turn on, transient upsets, and the commissioning process. The position of the window, and the effects of different beam currents should also be simulated. The effects on the beam of various control tolerances, and the effects on reliability of different generator sizes should also be modeled. A first-order RAMI analysis of the SC KF systems should also be performed. For the couplers and windows, we should scale the design of the KEK systems to 700 MHz and use that as our base design. We should also design and build a back up, and test both at high power. We shall also keep up with the progress at Cornell, SLAC, KEK, and the commercial window makers. The position of the window should be decided by considering operation with and -without beam, and also during transients and turn on, as well as considering what happens under high power processing of the cavities.

The conclusion is that the development required for a super conducting APT system has been done successfully before on other accelerators, so the risk in the project is small. f. 7*//«-"'^° (P. fa**)

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rf Power/Coupler (kW) J 25 125 125 250 250 400 J SO Power Source Klystrode Klystron Klystron Klystron Klystron Klystron < Power / Source (kW) 125 250 500 500 1000 800 2 SO No. of Couplers / Source 1 2 4 2 4 2 Cost of rf Power ($/W) 4.66 2.94 2.25 2.03 1.57 1.65 4-66 AC-to-rf Efficiency 0.700 0.585, 0.585 0.585 0.585 0.585 Total rf Power (MW) 86.76 86.76 86.76 87.26 . 87.26 87.61 Total No. of Power Sources 558 279 140 175 88 129 Total Length (m) 756 756 756 594 594 540 Dissipated Power (kW) 5.41 5.41 5.41 5.83 5.83 6.14 7.7 552 492 418 378 367

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1- A M*-. COOLP^ -6***- SYSTEM INTEGRATION WORKING GROUP System Integration Workshop Session Summary

Tom Moore, Klaus Bongardt Co-chairmen

Task of the session was weakly defined as "Systems Integration". This was interpreted by the chairmen as "any subject not covered by the two other sessions, allowing some overlap, but addressing systemic issues versus specific technological solutions." The firsttas k of the group was to define the scope of the session. Monday's efforts were aimed at reducing the subject list to one that could be addressed in the next few days. The focus was on identifying information necessary to support the September 1995 SCRF Feasibility Report and identification of any other significant technological risks, compared to normal conducting structures. M. Prome presented the thinking at Saclay regarding SCRF applied to an application very similar to APT. His conclusion thus far was that SCRF represented significant cost savings and was worth while pursuing. M. Prome's presentation was used as a starting point for ' the session discussion. Conclusions: Re: Failure of RF systems. Normal conducting system installs 7 klystrons and uses 6. Superconducting system should install 15% gradient and 15% peak power safety margin. Consider scenarios using installed margins to compensate for loss of accelerating structure or RF. Re: Confidence in safe operation. We are confident no greater risk than that faced by NC design. Cavity input coupler should have at least 30% design margin in power and field. Cryostat trips: Using current CEBAF experience (1 trip per 10 days, 4 hour downtime per trip) projected to APT shows that 2% of the 25% non-availability budget could be used by the cryogenics system. CEBAF expects that the experience will get better as a more stable operating environment is achieved. Design advice from CEBAF: Put all the complexity in the cryostat, make external systems simple. Re: Failure scenarios resulting in total shutdown >= 1 year. The participants were unable to postulate any technical Mure that would lead to a shutdown >= 1 year. The one example that came close was the loss of a cryogenics coldbox. Even that one can be circumvented with a redundant box. Re: Control Systems.

Different than that forNC but not more difficult.

Re: Commissioning.

Not more difficult than NC. •

Re: Operating considerations. APT is a production facility not an research facility. Therefore, needs more operating staff than a research establishment, requires addition of cryogenics expertise (for accelerator).

Requires SCRF support facility for cavity/cryomodule processing. Unlike klystrons where there is a world market for the support technology, APT SCRF components will be unique where the benefit of an external market and technological support will not exist.

Re: APT schedule.

Integrated SCRF APT program looks feasible given proper funding profiles. Components can be designed and tested without beam to a high confidence.

Low beta cavities can be ready in the time required to build Front End Demonstrator.

Re: Cost Metrics.

Look for technology/cost break points i.e. where changes in parameters result in disproportionate increases in cost.

RF power output vs. package size. Frequency.

RF Generator Efficiency.

Lifetime guarantees

Different technologies

Re: Program Strategies. Trades between development, capital and operating costs. Total cost over lifetime needs to be balanced with available funding realities and program definitions. Re: Cryostat. Cost a function of: Frequency. Operating temperature. Focusing elements in cryostat. Number of RF feedthroughs. Heat shield technology. Magnetic shielding (earth, stray, residuals). Re: R&D Program. Develop recovery scenarios for cavity failure (for any reason). Install 805 MHz cavity on LAMPF, run it, learn about it, make it fail and understand why. Answer generic questions about effects of beam loss. Develop a flexible RAMI model. Develop cold instrumentation/beam diagnostics. OVERALL SUMMARY Session participants could not identify any "show stoppers." SCRF has the following benefit potential: Reduced RF power. Shorter physical structure. Reduced operating cost (mostly electrical). Reliable and easy operation (per CEBAF). Identified problems have work-around solutions. Careful early system engineering will help NC or SCRF accelerator. # -WOfe. O^^^JL

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EUROPEAN SPALLATION NEUTRON SOURCE Superconducting Accelerator Module General Layout

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Energy of rf~ MeV « P 0.428 0.57 0.79 /• 0.9 • ' Epeak / EoT 2.59 2.12 1.87 1.81 Hpeak / EoT Ce/MV/m 52.2 44.9 34.5 •34.2 r/Q Q/m 236 293 360,- 387 Transit time T 0.764 0.751 0:737 0.732 Q (design) 3*109 3*109 3*109 3*109 Qext ?.6*105 6.2*105 5.2* 105 4.9*105 QL 3.8*105 3.P105 2.6*105 2.4M05 Afl/2 H 458 564 675 720 Tfield msec 0.69 0.56 0.48 0.44

E0T W/m 10 io • 10 ; 10 Operational Costs

Version A B C D Total RF power MW 10,5 5,6 6,6 19,4 Efficiency of klystron % 55 Efficiency of modulator % 85 Wall plug power MW "22,3 12,0 14,1 41,5 Hours of operation per year h 6000 Energy consumption per year KWh 13,4*107 7,2* 107 8,5*107 24,9* 107 forRF

Life time of a klystron a 4 Assuming 25 years of opera• tion the klystrons have to be 5 replaced Klystrons to be renewed 285 100 120 525 Cost of klystrons MDM 171 78 94 315

Capacity of refrigerator KW __ 2,7 2,7 Efficiency compared to % 20 Carnot-cycle 4.3 K Wall plug power MW ._ 0,88 10,88 Hours of operation per year Std. — 6300 — Energy consumption per year KWh 5,6* 106 5,6* 106 __

Price of one KWh DM 0,20 Costs for electrical power per MDM 26,8 15,5 18,1 49,8 year Costs for electrical power in MDM 302 171 200 561 10 a and for renewing of klystrons as above, but in 25 a MDM 841 466 546 1560

* Investment plus operational MDM 689 369 439 1308 costs in 10 a as above, but in 25 a MDM 122S 664 785 2307 Capital Costs

Version A • B C D Cost effective length of m 620 1250 accelerator structures No of cryo-modules 96 96 Price per metre nc structure MDM 0.25 0.25 Price of cryo-module MDM 0.7 0.9 Tools for cryo-module MDM 8 8 Total costs for structures MDM 155 76 94 312

No of klystrons 57 20 24 105 Price of one klystron MDM 0,6 0,78 0,78 0,6 modulator MDM 1,5 components like MDM 0,5 1,3 1,3 0,5 waveguides, circulator, T, etc. Price of a klystron channel MDM 2,6 3,6 3,6 2.6 Total RF-costs MDM 148 72 86 273

Refrigerator MDM — 9 9 —

Length of tunnel (= Length of m 670 330 470 1300 accelerator + 50 m) Price per metre tunnel MDM 0,125 Total costs of tunnel MDM 84 41 59 162

Total investment costs MDM 387 198 239 747 Accelerator Parameters

Version A B C D Material Copper Niobium Niobium Copper Frequency MHz 700 350 350 700 Initial energy MeV 150 100 Final energy MeV 1334 2668 Operating temperature K 290 4,3 4.3 290 Average bunch current mA 60 30 Duty cycle % 6,2 Effective accelerating gradient MV/m 2,4 8-10 8-10 2,4' Synchronous phase deg. -30...-25 -10 -10 -30... -25 No of cells per structure 30 2 4 30 No of structures 114 192 192 210 Aperture cm 4,4 10 10 4,4 Total length of accelerator m 620 280 420 1250

Peak RF power for beam MW 70 acceleration Dissipated RF power in MW 96 0.002 0.004 190 structures ^ Peak power of a klystron MW 3 4 4 j No of structures per klystron 2 16, 14, 12 24*8 2 10, 12*8 No of klystrons 57 20 24 105 Peak RF power of one input KW 3000 465 505 3000 coupler 27.4.95 Stiffening of a 350 MHz Cavity

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Advantages of superconducting structures are *

• large aperture small non-linear forces low beam losses

«> low frequency no frequency jump from low to high energy part of accelerator

* high efficiency low costs

for high power applications cw operation possible

Problems

high power input couplers R&D is necessary, today only 200 KW can be ATTENDEE LIST Page '

Last Name First Name Affiliation Address Phone Fax e-mail Cho Yanglai ANL Argonne National Laboratory 708-252-6616 708-252-4007 [email protected] 9700 South Cass Ave. Argonne, IL 60439

McMichael Gerry ANL Argonne National Laboratory 708-252-9231 708-252-4007 [email protected] 9700 South Cass Ave. Argonne, IL 60439

Ruggiero Alessandro BNL Brookhaven National Laboratory 516-282-2613 516-282-7650 [email protected] 12 South Upton Upton, NY 11973

VanTuyle Greg BNL Brookhaven National Laboratory 516-282-7960 516-282-7650 12 South Upton Upton, NY 11973

Lagniel Jean-Michel CEA CEA Saclay 33-1-69-08-5365 33-1-69-084858 [email protected] CEA-CENS 91191 Gif sur Yvette Cedex France Prome* Michel CEA CEA Saclay 33-1-69-08-7308 33-1-69-08-7312 CEA-CENS 91191 Gif sur Yvette Cedex France Bohn Courtlandt CEBAF CEBAF 804-249-7658 12000 Jefferson Ave. Newport News, VA 23606

Delayen Jean CEBAF CEBAF 804-249-7420 804-252-4007 12000 Jefferson Ave. Newport News, VA 23606 ATTENDEE LIST Page ___

Last Name First Name Affiliation Address Phone Fax e-mail Hutton Andrew CEBAF CEBAF 804-249-7396 804-249-5024 [email protected] 12000 Jefferson Ave. Newport News, VA 23606

Leemann Christoff CEBAF CEBAF 804-249-7554 804-249-5024 12000 Jefferson Ave. Newport News, VA 23606

Reece Charles CEBAF CEBAF 804-249-7658 [email protected] 12000 Jefferson Ave. Newport News, VA 23606

Padamsee Hassan Cornell Cornell University 607-255-4951 607-254-4552 hsp@crnlns Newman Lab. Ithaca, NY 14853

Bishop Bill DOE Department of Energy 202-586-0046 202-586-1567 [email protected] Independence Ave, SW Washington, DC 20585

Boggs Ben DOE Department of Energy 202-586-8281 Independence Ave, SW Washington, DC 20585

Britt Chip DOE Department of Energy 202-254-5351 [email protected] Independence Ave, SW Washington, DC 20585

Gerardo Jim DOE Department of Energy 202-586-1670 Independence Ave, SW Washington, DC 20585 ATTENDEE LIST Page

Last Name First Name Affiliation Address Phone Fax e-mail Rodgers Ron DOE Department of Energy 803-644-6915 Independence Ave, SW Washington, DC 20585

Stack Steve DOE Department of Energy 202-586-0791 Independence Ave, SW Washington, DC 20585

Wad Tom DOE Department of Energy 202-586-4612 [email protected] Independence Ave, SW Washington, DC 20585

Bongardt Klaus ESS ESS 49-2461-61-2305 49-2461-61-2470 [email protected] Forschungszentrum Juelich 52425 Juelich • Germany Pabst Michael ESS ESS 49-2461-61-3675 49-2461-61-2470 [email protected] Forschungszentrum Juelich 52425 Juelich Germany Lombardi Augusto INFN Instituto Nazionale Di Fisica Nucleare 39-49-8292358 39-49-641925 [email protected] Laboratori Nazionali Di Legnaro Via Romea 4 35020 Legnaro (PD, Italy Pisent Andrea INFN Instituto Nazionale Di Fisica Nucleare 3945-829-2352 39-49-641925 Laboratori Nazionali Di Legnaro Via Romea 4 35020 Legnaro (PD, Italy Ito Nobuo JAERI JAERI 81-292-82-5461 81-292-82-5663 [email protected] Accelerator Engineering Laboratory Japan Tokai-mura,Naka-gun, Ibaraki, 319-11 ATTENDEE LIST Page

Last Name First Name Affiliation Address Phone Fax e-mail Noguchi Shuichi KEK KEK 81-298-64-5230 81-298-64-3182- 1-1 Oho Tsukuba-shi, Ibaraki-ken, 305 Japan Yamazaki Yoshishige KEK KEK 81-298-64-5202 81-298-64-3182 [email protected] 1-1 Oho Tsukuba-shi, Ibaraki-ken, 305 Japan Anderson Jim LANL Los Alamos National Laboratory 505-667-1410 505-667-4344 [email protected] MS H813 Los Alamos, NM 87545

Barber Ron LANL Los Alamos National Laboratory 505-667-0958 505-667-3559 [email protected] MS H813 Los Alamos, NM 87545

Cappiello Mike LANL Los Alamos National Laboratory 505-665-1558 505-6674344 mcappiello® lanl.gov MS H813 Los Alamos, NM 87545

Chan K. C. Dominic LANL Los Alamos National Laboratory 505-665-0376 505-667-8207 [email protected] MS H813 Los Alamos, NM 87545

Fox Will LANL Los Alamos National Laboratory 505-667-1510 505-665-1687 [email protected] MS H813 Los Alamos, NM 87545

Gray Ed LANL Los Alamos National Laboratory 505-667-0700 505-665-6590 [email protected] MS H813 Los Alamos, NM 87545 ATTENDEE LIST Page

Last Name First Name Affiliation Address Phone Fax e-mail Jameson Bob LANL Los Alamos National Laboratory 505-665-2275 505-667-0919 [email protected] MS H813 Los Alamos, NM 87545

Jason Andy LANL Los Alamos National Laboratory 505-667-2842 505-665-6590 [email protected] MS H817 Los Alamos, NM 87545

Krawczyk Frank LANL Los Alamos National Laboratory 505-667-1958 505-665-6590 [email protected] MS H817 Los Alamos, NM 87545

Lawrence George LANL Los Alamos National Laboratory 505-667-9349 • 505-667-4344 [email protected] MS H813 Los Alamos, NM 87545 • Lisowski Paul LANL Los Alamos National Laboratory 505-667-7106 505-667-4344 lisowski@ lanl.gov MS H813 Los Alamos, NM 87545

Lynch Mike LANL Los Alamos National Laboratory 505-665-2435 505-665-2818 mtlynch@ lanl.gov MS H827 Los Alamos, NM 87545

Nath Subrata LANL Los Alamos National Laboratory 505-665-1953 505-665-6590 [email protected] MS H817 Los Alamos, NM 87545

Rees Dan LANL Los Alamos National Laboratory 505-665-2802 505-665-2818 [email protected] MS H827 Los Alamos, NM 87545 ATTENDEE LIST Page

Last Name First Name Affiliation Address Phone Fax e-mail Rusnak Brian LANL Los Alamos National Laboratory 505-667-9854 505-665-6590 [email protected] MS H817 Los Alamos, NM 87545

Schrage Dale LANL Los Alamos National Laboratory 505-667-1953 505-665-6590 [email protected] MS H817 Los Alamos, NM 87545

Shafer Bob LANL Los Alamos National Laboratory 505-667-5877 505-665-6590 [email protected] MS H817 Los Alamos, NM 87545

Shapiro Alan LANL Los Alamos National Laboratory 505-667-5074 505-665-6590 [email protected] MS H817 Los Alamos, NM 87545 * Swensen Erik LANL • Los Alamos National Laboratory 505-665-5101 505-667-3559 eswensen@ lanl.gov MS H817 Los Alamos, NM 87545

Tallerico Paul LANL Los Alamos National Laboratory 505-667-1197 505-665-2818 [email protected] MS H827 Los Alamos, NM 87545

Thiessen Arch LANL Los Alamos National Laboratory 505-667-8991 505-667-7920 [email protected] MS Los Alamos, NM 87545

Wangler Tom LANL Los Alamos National Laboratory 505-667-3200 505-665-6590 [email protected] MS H817 Los Alamos, NM 87545 ATTENDEE LIST Page

Last Name First Name Affiliation Address , Phone Fax e-mail Watson Jerry LANL Los Alamos National Laboratory 505-665-2875 ' 505-665-8604 [email protected] MS H850 Los Alamos, NM 87545

Belser Curt LLNL Lawrence Livermore National Laboratory 510-422-6750 P. 0. Box 808 - 7000 East Ave. Livermore, CA 94550

Kriesler Mike LLNL Lawrence Livermore National Laboratory 510422-0920 510423-8086 krieslerl® llnl.gov P. 0. Box 808 - 7000 East Ave. Livermore, CA 94550

• Moore . Tom LLNL Lawrence Livermore National Laboratory 510-423-5774 P. O. Box 808 - 7000 East Ave. Livermore, CA 94550

Pennock Steven LLNL Lawrence Livermore National Laboratory 510422-8937 [email protected] P. 0. Box 808 - 7000 East Ave. Livermore, CA 94550

Slaughter Dennis LLNL Lawrence Livermore National Laboratory 510-422-6425 510423-5998 P. O. Box 808 - 7000 East Ave. Livermore, CA 94550

Yee Jick LLNL Lawrence Livermore National Laboratory 510422-8700 P. 0. Box 808 - 7000 East Ave. Livermore, CA 94550

Appleton Bill ORNL Oak Ridge National Laboratory 615-574-0323 P. O. Box 2008 Oak Ridge, TN 37831-6240 ATTENDEE LIST Page

Last Name First Name Affiliation Address Phone Fax . e-mail Mazarakis Mike Sandia Sandial National Laboratory 505-845-7003 505-844-7003 P. O. Box 5800 Albuquerque, NM 87185

Funk L. Warren Savannah R Savannah River 214-223-4258 [email protected] 1404 Mantlebrook Dr. DeSoto.TX 75115

Heinrichs Horst SLAC Universitaet of Wuppertal Gausstrasse 20 W-5600 Wuppertal 1 Germany Herrmannsfeldt Bill SLAC Stanford Linear Accelerator Center 415-926-3342 415-926-4999 P. O. Box 4349 Stanford, CA 94305

Klein Horst UNIV OF FR University of Frankfurt 49-69-798-3489 der Johann-Wolfgang-Goethe Univ. D-6000 Frankfurt am Main 1 Robert Mayer Strasse 2-4 Germany