TTC2020 Feb. 4~7 CERN Technical Challenges for SRF of RAON M. Kwon on behalf of RISP Rare Isotope Science Project Institute for Basic Science Daejeon, Korea Contents • RAON Introduction • Technical Challenges • Lesson Learned and Summary 1. Introduction Rare Isotope Science Project (RISP) Goal: To build a heavy ion accelerator complex RAON, for rare isotope science research in Korea. * RAON - Rare isotope Accelerator complex for ON-line experiments Budget: US$ 1.3 B - accelerators and experimental apparatus (~450M) - civil engineering & conventional facilities (~850M) Period: 2011.12 ~ 2021.12 System Installation Project Providing high intensity RI beams by Development, installation, and commissioning of the ISOL and IF accelerator systems that provides high-energy (200MeV/u) ISOL: direct fission of 238U by 70 MeV and high-power (400kW) heavy-ion beam proton IF: 200 MeV/u 238U (intensity: 8.3 pμA) Providing high quality neutron-rich Facility Construction Project beams e.g., 132Sn with up to 250 MeV/u, Construction of research and support facility to ensure up to 109 particles per second the stable operation of the heavy-ion accelerator, experiment systems, and to establish a comfortable research environment Providing More exotic RI beam ※ Accelerator and experiment buildings, support production by combination of ISOL facility, administrative buildings, and guest house, and IF etc. 1. Introduction Accelerator Systems Parameters Unit QWR HWR SSR1 SSR2 bg - 0.047 0.12 0.30 0.51 F MHz 81.25 162.5 325 325 KoBRAApertureBeam Line mm 40 40 50 50 SCL2(SSR1) SCL2(SSR2) Injector QRs Ohm 21 42 98 112 R/Q Ohm 468 310 246 296 Vacc MV 0.9 1.3 1.9 3.6 Epeak/Eacc 5.6 5.0 4.4 3.9 Cav. Op. T # of # of Cryomodule (K) Bpeak/Eacc 9.3 8.2 6.3 7.2 cav. CM 9 Qcalc/10 - 2.1 4.1 9.2 10.5 QWR 1 22 4.5 SCL3 2 13+2 2.05 Temp. K 4 2 2 2 HWR 4 19 2.05 SSR1 3 23 2.05 SCL2 SSR2 6 23+2 2.05 SCL3 SCL3 (HWR) (QWR) Cyclotron IF System 1. Introduction Building Layout Control Center ECR IS Utility SCL1 ISOL System HPMMS/ IF CLS SCL3 SCL2 System BIS μSR NDPS KOBRA Cyclotron HRS LAMPS 1. Introduction Rare Isotope Science Project (RISP) Introduction • RAON Project is a “Green Field” Project - Largest Scientific RI Project ever in Korea - Newly assembled organization - Lack of human resources - Lack of experienced experts in SRF technology - No pre-R&D or pilot R&D project - Civil construction started 5th-year into the project 1. Introduction Rare Isotope Science Project (RISP) • To Reduce Risks of a “Green Field” Project - Strong support inevitable from foreign experts and institutes for design, prototyping and tests - Tendency to take more conservative solution to reserve larger safety margins 1. Introduction Rare Isotope Science Project (RISP) • However,Introduction a “Green Field” Project can open up new opportunities in - adopting new technologies for public and private sectors - attracting young scientists and engineers to get trained in new technical areas - challenging domestic companies for industrializing new technologies 2. Technical Challenges Challenging Issues “Carrying out a project is a series of decision-making process on the challenging issues” 2. Technical Choice of HWR and SSR Challenges • RAON minimized the number of QWR because the QWR deflects the beam, and adopted HWR for low energy linac. - HWR is widely chosen for 0.09 ≤ b ≤ 0.3. • High intensity linacs employ HWR at low energy - IFMIF : RFQ + HWR (deuteron 125 mA) - PIP-II (Fermilab) : RFQ + HWR + SSR (proton 25 mA peak) - CADS (China) : RFQ + HWR + SSR (proton 10 mA) - RAON : RFQ + QWR + HWR + SSR • RAON adopted SSR for high energy linac because - Spoke cavity is widely chosen for 0.15 ≤ b ≤ 0.6 - Spoke cavity offers large beam aperture and reduces beam loss on cavities (RAON SSR aperture diameter is 50 mm) but operation with variety of cavities, couplers and interfaces is the cost 2. Technical SCL Cryomodule Design Challenges Long cryomodule • Long cryomodules contain solenoid both cavities and solenoids. • Short cryomodules contain cavities only and quadrupoles are outside. Short cryomodule quadrupole 2. Technical Pros and Cons Challenges • Long-Cryomodule Design - Linac length is shorter especially in the low beta section (FRIB is ~15% shorter than RAON). - Solenoid alignment in cryomodule is not trivial. - Beam loss can be high before orbit correction. - Beam operation is not possible when 1~2 cryomodules are removed for repair. - SC cavities are close to SC solenoids and stray field on cavity (~15 G) can degrade the cavity performance. Need 4K magnetic shield for cavities. - SC solenoids can magnetize cryomodule components. • Short-Cryomodule Design - Linac length is slightly longer in the low beta section. - Alignment of quadrupoles is easy (< ± 0.15 mm). - Beam loss is low even before orbit correction. - Beam operation is possible even when 1~2 cryomodules are removed. - SC cavities are separated from quadrupoles and there is no issue of B field of quadrupoles. 2. Technical Orbit Deviation Comparison Challenges Before, After orbit correction Long CM Short CM • For long-CM design, maximum orbit deviation is ~17 mm (before orbit correction) and ~6 mm (after orbit correction). Cavity aperture radius is 20 mm. • For short-CM design, maximum orbit deviation is ~ 7mm (before orbit correction) and ~ 2 mm (after orbit correction). 2. Technical Challenges Design to Manufacturing Processes Conceptual Prototype design manufac. Engineering Review Test design change Engineering Call for design Tender Review by domestic experts Pre-production Review by foreign Review manufac. experts Engineering Test design change Serial production 2. Technical Challenges Design to Manufacturing Processes . QWR prototype case Static thermal load Total thermal load @ 6.1 MV/m Eacc(MV/m) 6.1 6.4 7 Q (W) 9.9 13 23.7 Cavity: 2nd prototype(RI), rd 3 prototype(Vitzro tech) Total thermal load at various Eacc Tuner: 2nd prototype (Mirho) Coupler: 1st prototype (Toshiba) Target total thermal load @ 6.1 MV/m: 25 W Cryomodule: 2nd prototype (Vitzro tech.) 2. Technical Challenges Design to Manufacturing Processes . HWR prototype Static thermal load Total thermal load @ 6.6 MV/m Static Dynamic Total thermal load thermal load thermal load 1.4 W (cavity#1) 6.6 W 12.8 W Cavity: 3rd prototype(Viztro tech.) 4.8 W (cavity#2) Tuner: 2nd prototype (Montrol) Coupler: 2nd prototype (Toshiba, Viztro tech.) Cryomodule: 2nd prototype (Vitzro tech.) Target total thermal load @ 6.6MV/m: 14.1 W 2. Technical PreChallenges-production phaseDesign and to test Manufacturing Processes . Pre-production • QWR: 2 sets of cryomodules (2 cavities, 2 couplers, 2 tuners, 2 cryostats) • HWR: 2 sets of cryomodules (6 cavities, 6 couplers, 6 tuners, 1 cryostat each) • Vertical test is done for bare and dressed cavities Modification of design, improvement of manufacturing procedure Verification of manufacturer’s ability Confirmation of final design after the performance test . Vertical and Horizontal test • Vertical and Horizontal test is done in SRF test facility of RISP (Munji and Sindong) • Vertical test is done for the dressed cavities only during serial production • Operation of vertical and horizontal test system (including cryogenic system) will be done by RISP’s personnel 2. Technical Challenges Design to Manufacturing Processes Changes for pre-production cavities . Design modification to reduce the df/dp of QWR cavities Calculated Measured (Hz/mbar) (Hz/mbar) -33.4#2-1 Prototype (bare) -37.9 -37#3-1 - beam port free -31#3-2 Prototype (jacketed) 33.6#1-1 36.7 - beam port free 36.5#2-1 Pre-production (jacketed) A B 12.7 12.0#7 - beam port free Prototype 115.7 148 Pre-production (jacketed) 2.0#2 -4.6 Pre-production 96.7 120 - beam port fixed -2.7#5 . Improvement of welding procedure for LFD of QWR cavities Calculated Measured [Hz/(MV/m)2] [Hz/(MV/m)2] -20#1-1, -32.7#2-1, prototype (bare) -17.4#2-2, -44.6#3-1 - Beam port free #3-2 -16.4 -14.7 Pre-production -15 ~ -21 - Beam port free Prototype Pre-production 2. Technical Challenges Design to Manufacturing Processes . Design change to reduce peak field of HWR cavities Field emission starts below 6 MV/m while operating gradient is 6.6 MV/m 1.0E+10 1.0E+09 Qo 1.0E+08 1.0E+07 0 2 4 6 8 10 Eacc [MV/m] Parameter Original Modified Rounding of Beam tube 5mm 10mm H of Beamport cup 52.5mm 49.5mm Diameter of Ring 120mm 130mm Width of Ring 65mm 67mm Rounding of Ring 30mm 33mm Epeak/Eacc 5.54 5.23 2. Technical Challenges Control Bandwidth Decisions Reason Impacts Epeak 30 MV/m 35 MV/m by TAC Cost benefit Increase of Δf 36 % due to LFD Determining thickness of Nb of 3mm Increase of df/dp and LFD Cost benefit (after pressing, ~2 mm) (for 4 mm, df/dp, LFD 56 % reduction) Purchasing Nb in advance PM’s decision Cause to limit for design change He pressure fluctuation Changing op. temperature of QWR Cost benefit 2 K: ±0.1~0.3 mbar / 4 K: ±1 mbar from 2.1 K to 4.5 K Increase of Δf for 3~10 times Tuner fix only on flange He jacket material to be STS Cost/process benefit tuner/stiffening design constraint Beam tube size: 40mm Reduction of beam loss (FRIB:36, TRIUMF:25) df/dp, LFD proportional to the size of beam cup (symmetric E-field) Beam cup size: 120mm Difficult to test simulating real environment (3 Bar Different environments between Space and utility of He pressure, 1.3 bar inner pressure, vibration tunnel and test facility availability source, etc) Hold safety margin by taking more conservative design 2.