High efficiency – high perveance Klystron (X-band) EnEfficiency RF sources Workshop Cockcroft Institute Franck Peauger CEA/IRFU/SACM/LISAH June 3, 2014 www.cea.fr www.cea.fr OUTLINE . Context and objectives . New klystron concept . Simulation codes . Klystron development plan 2 . Context and objectives . New klystron concept . Simulation codes . Klystron development plan 3 WORK DONE UNDER TASK 12.3 OF EUCARD2 WP12 Innovative RF Technologies 2013 - 2017 « In this sub-task, CEA will develop and search for innovative concepts of X band RF power sources and components. The objective is to propose affordable and reliable solutions for future testing capabilities for the CLIC accelerating structures. The task includes the design and the fabrication of prototype RF devices to demonstrate the feasibility of the new concepts proposed. » Juliette PLOUIN: CEA project leader for this sub-task Budget available to build a (small) part of the RF power source or component Fully oriented towards an R&D activity 4 A STRONG MOTIVATION WITH A MORE GENERAL INTEREST • Some important projects (XFEL, ESS, CLIC-drive beam, FCC…) search for “green technologies” and so require ultra-high efficiency RF sources • Modulators are now close to 90% efficiency. Microwave tubes are one of the major weak point in the energy consumption chain • A road map to reach the 90% efficiency horizon have been established by Igor at different frequencies • Our Eucard2 task is well in agreement with this road map • This project is also an occasion to acquire knowledge and experience on RF sources “in-lab design” and why not “in-lab fabrication” in Europe (like what is done at SLAC or on HV modulator at CERN for example) 5 LIST OF POSSIBLE DEVICES Microwave vacuum tubes for X band and high peak power O type Gyro M type Gridded tubes devices tubes tubes Travelling Locked Carcinotron Klystron Gyroklystron IOT wave tube Magnetron Single beam “affordable and reliable” klystron = Multibeam reduced surface fields klystron (DC and RF) Sheet beam “high efficiency” klystron = Optimal beam / RF interaction Hollow beam 6 klystron X-BAND 50/75 MW KLYSTRON (USA) • Development started in 80’s for linear collider studies at SLAC • XC series: 100 MW design, 65 to 72 MW measured • XL series for NLCTA: 50 MW, 410 kV – 305 A, reduced perveance of 1.2µA/V1.5, 40% efficiency, Jongewaard • XL4 : 11.424 GHz produced in 15 units • PPM focusing investigated and combined with high efficiency (60%) but with limited success of SLAC, E.SLAC, of • In 2008 – 2011: XL5 : scaling of XL4 at 11.9942 GHz for CLIC, PSI and Trieste - 5 tubes built courtesy • Since 2011: XL5 transferred to industry : CPI VKX8311A Image: - first tube tested at SLAC in 2013 7 N. Catalan, CLIC workshop 2014 X-BAND 75 MW KLYSTRON (JAPAN) Same parallel development at KEK/TOSHIBA for NLC/JLC Spec (target): 75 MW, µPerv. 0.8, 60% efficiency More results with the PPM focusing version 10 tubes tested S. Fukuda, KEK, 2005 Image: courtesy of TOSHIBA 8 X-BAND 150 MW MULTIBEAM KLYSTRON (JAPAN) Annular cavities working on a HOM “Realistic design” to reduce the beam voltage A. Larionov et al., KEK 9 9.3 GHZ – MEDIUM POWER « COMMERCIAL » KLYSTRON 10 SHEET BEAM KLYSTRON Explored in W-band, S-band and at 1.3 GHz by SLAC PPM focused X-band tube under development at CPI to lower the voltage Also investigated in China at IECAS A. Jensen, SLAC, IVEC2013 T. Johns et al., CPI D. Zhao et al., IECAS11 ANNULAR BEAM KLYSTRON Developed by CCR at 1.3 GHz – 10 MW Very high perveance (3.3 µA/V^1.5) and high efficiency (65%) Zero compression gun and high current density cathod Try to avoid diocotron instabilities M. Read et al., CCR 12 XBOX3 TEST STAND AT CERN XBOX3 will use four Medium Power X-band klystrons recombined and compressed to produce a 50 MW power level This smart concept is well adapted to the reliability and affordability we are looking for and it will constitute the basis of our study I. Syratchev, G. McMonagle, N. Catalan Lasheras • 4 turn-key 6 MW, 11.9942 GHz, 400Hz power stations (klystron/modulator) have been ordered from industry. Medium power x-band RF sources have• alsoThe f iarst wider unit is interestscheduled in to FELarrive and at C ERN in October medical applications 2014. The full delivery will be completed before13 Ju ly 2015. XBOX 3 AT CERN CERN is ordering commercial products for XBOX3 (4 units of each) No particular R&D is required and delivery time is short TOSHIBA klystrons SCANDINOVA parameters Modulator parameters Peak power: 6 MW Peak RF power: 8.0 MW Beam Voltage: 150 kV Pulsed voltage: 175 kV Beam current: 90 A Pulse current: 115 A Average power: 12.4 kW Average power: 50 kW Efficiency: 47.5% Pulse length (flat): 5 sec Rep. rate: 400 Hz 14 A VERY CHALLENGING OBJECTIVE Our proposal is to study and design a 12 GHz single beam klystron able to deliver a peak power of 12 MW with a pulse duration of 4.5 s to double the testing capability of XBOX3 It should be compatible with the Scandinova modulator ordered for XBOX3 in order to do fully qualify the klystron at CERN. A possible operating point could be: - Vk = 170 kV - Ik = 100 A -> µP = 1.4 µA/V1.5 - efficiency > 70 % -> Pout = 12 MW A new klystron concept is required P. Guidee, Thales, 2001 A classical solenoid based focusing system would be considered for this first step. The klystron should be designed to operate at a pulse repetition rate of 400 Hz minimum and - why not -, up to 1 kHz, a highly interesting repetition frequency for future FEL projects 15 . Context and objectives . New klystron concept . Simulation codes . Klystron development plan 16 THE ADIABATIC CONCEPT . A system is called adiabatic when the external forces vary more slowly than the interaction forces in the system. The dynamics of the system is then a succession of equilibrium states and the entropy does not increase. Example in thermodynamic: adiabatic if no heat exchange with the external medium: the piston velocity must be smaller than the speed of sound in the gas . In our case, the external forces are the beam induced bunching forces and the interaction forces are the space charge forces. 17 A PARALLEL WITH RFQS FOR PROTON LINAC An RFQ cavity is used in proton linac injector to bunch, focus and accelerate a continuous beam from few tens of keV to few MeV. It allows a beam transport in space charge regime (high intensity beams is possible) with very low beam losses. TE210 mode longitudinal modulation on the electrodes creates a longitudinal component in the TE mode that bunch and accelerate the beam bl In the IPHI RFQ (3 MeV, 6m, 352 MHz), around 350 cells are used to bunch the 18 beam PHASE SPACE DISTRIBUTION IN AN RFQ Along the 6m RFQ: At the RFQ exit: (MeV) dW dispersion Energy Phase (deg) The bunching process in an RFQ is adiabatic (« gentle » buncher) The RFQ preserve the beam quality, has a high capture (~90%) compare to a discrete bunching model (50%) 19 INCREASING THE NUMBER OF CAVITIES IN A KLYSTRON 10 cavities 20 cavities Efficiency 67.2 % Efficiency 78 % Length 197 mm Length 285 mm . The idea is also to maintain a classical perveance value of 1.4 µA/V1.5 (170 kV – 100 A) : high current leads to shorter plasma wavelengths (and so shorter structures) . In the design proposed, the cavities are weakly coupled to the beam (low R/Q) and largely detuned to 20 avoid strong bunching ANIMATION FROM AJDISK RESULTS (CHIARA MARRELLI) 5 cavities – 1 GHz optimized by C. Marrelli 20 cavities – 12 GHz optimized by F. Peauger 휇Perveance = 0.21 휇Perveance = 1.4 Pout ≈ 2.3 MW Pout ≈ 12.5 MW Efficiency 78. % Efficiency 78 % EXPECTED PERFORMANCES WITH 4 DIFFERENT DESIGNS Name Numbers R/Q TTF Efficiency Overall of cavities [Ohm] length [mm] AK10-2 10 20 to 50 0.683 67.2 % 197 AK14-1 14 20 0.683 68.5 % 221 AK20-3 20 27.4 0.688 74 % 285 AK20 20 12 0.72 78 % 285 70% efficiency . These design have been manually optimized and could be certainly fully improved by an automatic procedure. 22 EXPECTED DETAILED PERFORMANCES 14 CAVITIES STRUCTURE Output power for different cathod voltages Phase variation for 1% of cathod voltage change 14 -50 ∆∅ 175 kV – 104 A =9.4 °/kV 12 -55 ∆푉푘 171.7 kV – 101.5 A -60 10 170 kV – 100 A -65 -70 8 170 kV – 100 A 150 kV – 82.8 A -75 6 -80 -85 4 Outputphase (deg) -90 168.3 kV – 98.5 A Outputpower (MW) 125 kV – 63 A -95 2 -100 0 0 5 10 15 0 10 20 30 40 Input power (W) Input power (W) Efficiency at saturation for different cathod voltage Bandwidth Small signal 80 74 (Pin = 0.5 W) 170 kV – 100 A 70 70 60 66 50 62 Saturation (Pin = 10 W) 40 Gain (dB) 58 30 54 Efficiency at saturation (%) 20 50 120 130 140 150 160 170 180 11.97 11.98 11.99 12 12.01 12.02 12.03 Cathod voltage (kV) Drive frequency (GHz) 23 BUNCHING CAVITY DESIGN 2 j z E (z)dz b C z Ez (z)e dz R M Q 2U L / 2 E (z)dz z L / 2 Eigenmode F = 11.9108 GHz, Q = 2039 with copper Utot = 2.5735E-19 J R/Q = 23.9 ohm M = 0.6127 XY Plot 1 cav3 0.20 Curve Info ComplexMag_E Setup1 : LastAdaptive gap2='1mm' Phase='0deg' r1='9mm' ComplexMag_E_1 0.18 Setup1 : LastAdaptive gap2='1mm' Phase='0deg' r1='9mm' 0.15 0.13 0.10 Y1 [V_per_meter]Y1 0.08 0.05 0.03 0.00 0.00 5.00 10.00 15.00 20.00 25.00 Distance [mm] 24 INPUT / OUTPUT CAVITY DESIGN Input cavity Output cavity: many possibilities: Qx = 460 - Same as input cavities but with Qx = 20 (change of the iris dimensions) - Multicell output cavity: SW or TW - Other ideas ? (backward wave, recirculation, …) SLAC XL5 output cavity (4 cells, p mode) 25 .