15 th European Synchrotron Light Source RadioFrequency Meeting

15 th European Synchrotron Light Source Radio-Frequency Meeting 5 - 6 October, 2011 ESRF, Grenoble RF systems for Thom. X P. Marchand - Synchrotron SOLEIL

The Thom. X Project Compact source of hard X-rays (40 – 90 ke. V) Flux of up 1013 photons / sec, generated by Compton Back Scattering (CBS : collisions between e- bunches and laser pulses ω dif ~ 4 γ 2 ω laser ) Applications - Medical sciences (imaging + therapy) - Cultural heritage sciences (Louvre Museum, for instance) Compactness for accommodation in hospitals and museums Compactness Funding of 12 M€ for Phase 1 : building of a prototype feasibility proof Funding Phase 2 : industrialization Work supported by the EQUIPEX program from the Research Ministry, Région Ile de France, CNRS-IN 2 P 3 and University of Paris-Sud Contributions from LAL-Orsay CNRS-IN 2 P 3, SOLEIL, CELIA Bordeaux, ESRF, C 2 RMF-CNRS, UDIL CNRS, INSERM Grenoble, Thales TED, Institute Neel Grenoble LAL-Orsay & SOLEIL in charge of the accelerator complex, housed inside the former DCI building on the university site in Orsay (~ 5 km from SOLEIL)

Thom. X accelerator complex 7 m SR optics : 4 -fold symmetry Double Bend Achromat Interaction Region FP optical cavity 10 m Injection of a single e- bunch (20 m. A), which collides at each turn with laser pulses at the IP, inside the FP optical resonator X rays from CBS fast degradation of the e- beam quality storage for ~ 20 ms Injection rate of 50 Hz (after 20 ms, extraction to BD & new injection)

The LINAC Injector Photocathode RF gun : • Replica of the CERN-CTF 3 gun, built by LAL • Ec = 100 MV/m with 10 MW • Mg cathode (Q up to 1 n. C) • Laser : l = 266 nm, E ~ 100 µJ, st ~ 5 ps Accelerating structure : • LIL type (4. 5 m long) AS, spare from SOLEIL • P = 10 (20) MW E = 50 (70) Me. V 2. 5 cell 3 GHz gun RF Power source : • 35 MW TH 2100 klystron from Thales • Solid state modulator (3 µs, 50 Hz) • Power splitting : 10 MW Gun 20 MW AS Expected beam performance (PARMELA) • E ~ 50 Me. V (max 70) • s. E/E < 0. 4 % • en ~ 5 p mm. mrad HV modulator Klystron

RF system of the Storage Ring

SR RF parameters At 50 Me. V , Urad ~ 2 e. V / turn Pbeam ( Ib = 20 m. A ) ~ 0 • No power to be delivered to the beam ( s = 0) • RF system only generates VRF for suitable longit. acceptance Selected RF frequency 500 MHz Good compromise - VRF = 500 k. V 1 single cell cavity PRF (dis) ~ 35 k. W - Availability of power sources & other RF components - Reasonable equipment size - Zhom will dictate the choice of cavity design

HOM impedances and instability thresholds U rad ~ 0 damping ( ~ 1 s ) >> storage ( ~ 20 ms ) To preserve the beam quality Instability growth time , i > 20 ms Longitudinal HOM in resonance, il = 2 Qs E/e / (a Io Rs fm) Rs. fm (HOM) natural : 0. 1 - 1 M . GHz il ~ 10 µs !! Transverse HOM in resonance, it = 2 E/e / (b. T frev Io RT) RT (HOM) natural : 1 - 10 M / m it ~ 10 µs !! In both, longitudinal and transverse cases, damping of Zhom by a few 103 is required !! (more critical than in 3 rd generation LS x 10)

Cures to HOM impedances 1) De-Qing of the HOM (HOM couplers) a few 102 - 103 Not enough & cumbersome equipment around the cavity « DAMPY » cavity - ALBA PEP-2 cavity (LBNL)

Cures to HOM impedances 2) HOM tuning Prevent resonant excitation by the beam à ELETTRA cavity with its 3 tuning means - Temperature control of f. HOM - Lcav (mech. deformation) fo - Movable plunger on the equator • 1 single cavity • ~ No beam loading • Small circumference Power coupler Tw ± 0. 1°C Lcav Well suited to HOM tuning Ø Beam spectrum lines : df = 18 MHz Ø HOM resonance BW : a few 10 k. Hz Ø f. HOM (tuning) : a few MHz Rs ( f = 0) / Rs ( f ) = 1 + (2 Q f / f )2 A few 103 to 104 Ok for Thom. X Plunger

HOM Spectrum Ok Ok Ok l = 20 ms ELETTRA cavity L-HOM spectrum (9 modes) over the 18 MHz base band

RF power source VRF = 500 k. V, using 1 ELETTRA cavity PRF (dis) = 35 k. W At 500 MHz Klystrons, IOTs, Solid State Amplifiers (SSA) SOLEIL technology - Well proven (6 years op. ) - No HV - Modularity redundancy - … 35 k. W SSA of the SOLEIL Booster 147 modules of 330 W @ 352 MHz ~ 35 000 runing hours over 6 years Operational availability of 100 % Minor pbs on 5 modules only without impact on the operation H = 2. 50 m , = 2 m For Thom. X, make it at 500 MHz

SOLEIL - LNLS collaboration Two amplifiers of 50 k. W @ 476 MHz for the LNLS storage ring with components designed by SOLEIL (RF modules of 400 W) April 2010 : the SOLEIL - LNLS team in Campinas-Brazil, after successful tests of the amplifiers

LNLS 50 k. W RF plants The two 50 k. W SSA have run satisfactorily on the LNLS SR for ~ 1 year

SOLEIL R&D’s with SSA @ 352 MHz 6 th generation transistors (Vdc = 50 V) + SOLEIL expertise fast progress At 352 MHz, Pmod ~ 700 W, G > 20 d. B, > 70% [ Current LR 301 mod. (Vdc = 28 V) : P = 315 W, G = 13 d. B, = 62 % @ 352 MHz ] Huge improvement : Pmod x 2. 2 , better performance (G , , linearity) & thermal stress strongly reduced ( T : - 60 °C) longer lifetime Beg. 2009, transfer of technology agreement concluded with ELTA-AREVA à ESRF contract for 7 SOLEIL type amplifiers of 150 k. W (14 x 75 k. W towers) Ø June 2010 : A 10 k. W unit (16 modules) successfully tested at SOLEIL Ø June 2011 : First 75 k. W tower passed the acceptance tests ( ESRF ) SOLEIL SSA : Evaluate 6 th generation transistors of lower power (~ 330 W) from NXP & Freescale replace LR 301 with min. modification In view of storing 500 m. A using a single cryomodule : • Combination of two 180 k. W SSA for powering one cavity • Input power coupler (P > 300 k. W) developt CERN/ESRF/SOLEIL collab.

R & D’s with SSA @ frequencies other than 352 MHz Prototypes of 500 MHz module : P = 650 W, G = 18 d. B, η = 67 % Components design is completed Ø 1 x 50 k. W for Thom. X First tower : by the end of 2012 Ø 4 x 150 k. W for SESAME Extend the technology to frequencies from FM to L band Ø VALVO/SOLEIL set of circulators covering the whole freq. range Ø Prototype of 88 MHz module : P = 900 W, G = 25 d. B, η ~ 80 % Ø BBEF : 20 k. W CW – 1. 3 GHz SSA for the Beijing University Ø Collab. Agreement under finalization with CERN for a prototype of 20 k. W @ 200 MHz in anticipation of 2 x 1. 6 MW New features : Ø Modular high efficiency 230 V_ac / 50 V_dc power converters Ø Option for housing the complete SSA inside a cabinet Ø Waveguide-to-coaxial combiner (Wa. CCo) adjustable coupling Possibility of matching variable number of modules

Waveguide-to-Coaxial Combiner (Wa. CCo) 2 coaxial inputs dl WG output Ø Two 6 inches coaxial input ports (2 x 80 k. W) 1 WG output Ø Replace a coaxial combiner + a coaxial-to-WG transition Ø Design optimization with HFSS and Microwave Studio A 500 MHz prototype is being fabricated by BBEF Ø Movable SC can ensure a good matching for different configurations wit diff nb of dissipaters per tower or diff nb of modules per dissipater

Thom. X LLRF system – slow loops Compensation of slow perturbations >> fcav = 40 µs Conventional LLRF (frequency, phase, amplitude loops) Replica of the actual analogue SOLEIL design, adapted for 500 MHz Phase loop Frequency tuning loop Amplitude loop 3 d. B RF SWITCH 40 k. W AMPLIFIER Coupler Drive CAVITY 500 MHz PID RF ON / OFF PID Phase control o d. V d cav in df + Voltage control Tuning control cav - Vcav PID Tuner

Fast phase / energy oscillations Ø Injection errors, d. Ei , d i Ø Mismatch between injected bunch and RF bucket Ø HOM excitations Ø Transient beam loading - d = 8° ( divided by Gfbk ) (Ib : 0 - 20 m. A instantly) - Only first injections (stationary after ~ 1 s) Oscillations in phase & energy @ fs, the synchrotron frequency with damping time, d 1 / Urad d. E/E d. Ei d i d (t) t d i d Either Phase or Energy errors Phase & Energy oscillations (quadrature)

Fast phase / energy oscillations e- bunch length : 20 – 30 ps rms Laser pulse duration : 5 ps rms Synchro e- / laser t < 5 ps < 1° ( E / E)inj = 0. 5 % (LINAC) inj = 8° (AS) Without oscillation damping : Emittance growth Bad bunch / laser overlap Still amplified by mismatch & HOM Loss of efficiency in the e-/laser interactions @ IP q d ~ 1 s >> st = 20 ms ~ no natural damping during st q fs = 500 k. Hz >> BWcav = 25 k. Hz damping through the cav. impossible 3 means for generating some damping : 1) Longitudinal FB using an additional broad band cavity 2) Harmonic cavity Landau damping 3) Direct RF FB on the main cavity increase its effective BW (> 500 k. Hz) No need for additional cavity

Direct RF Feedback principle G - Pin + Z(ω) Ig C Rg Rs Ib Vc L With FB : ; At resonance ( r) , Gain limitation ( stability criterion ) Loop delay Ampli-cav distance Thom. X : ampli - cavity distance ~ 10 m T ~ 150 ns Glimit ~ 60 BW ~ 1. 5 MHz >> fs

Cavity transfer function with RF FB Amplitude [d. B] 0 -10 T = 150 ns -20 -30 Gain 0 -40 fr - f s -50 -60 495. 00 496. 00 497. 00 498. 00 499. 00 fr + f s 500. 00 501. 00 502. 00 503. 00 504. 00 505. 00 Frequency (MHz) T = 150 ns Frequency (MHz)

RF FB + fast beam phase loop BPM d G Phase comparator Ib 90° MO 500 MHz RFSwitch Driver AMPLI 50 k. W 3 d. B CAVITY Phase Shifter Interlocks RF FB BWcav x (1 + Go) > fs Modulate Vcav at f > fs Go Att - Phase comparison between Vc (PU cav) & Ib (BPM) - The error signal, d (+ 90°) controls a phase shifter Alternative : Modulate the MO with d BW ? Phase loop (BW > fs) PUcav RF feedback

Phase / energy oscillations with RF FB + fast phase loop inj = 10°, Go = 50, G = 5 , T = 150 ns Damped after 20 µs T_damping = 3 µs for G = 30 (stability limit)

Complete LLRF MO 500 MHz 3 d. B PA Att PID 50 k. W AMPLI RF SWITCH A Tuning control PID Coupler CAVITY Tuner Direct RF Feedback Phase control Go + Att PID - Beam PU Voltage control Beam phase G Conventional system with 3 « slow » loops around the cavity Frequency Amplitude Phase Oscillations @ fs (500 k. Hz) inj , HOM, … - Direct RF Feedback (G ~ 50) - Fast beam phase loop (BW > 500 k. Hz)

Summary & Conclusion RF system of Thom. X SR 1) One 500 MHz ELETTRA type cavity (HOM tuning) 2) 500 k. V with 35 k. W, supplied by a SOLEIL type SSA 3) LLRF : conventional system with 3 slow loops (fr , V , v) + high gain RF feedback & fast phase loop ( b) Rem : Thom. X is a small machine, but quite complex and challenging, in particular as regards to the electron beam dynamics Planning : RF equipment available for installation in Thom. X by mid-2013 - Amplifier & LLRF designed & supplied « turn key » by SOLEIL - Cavity one of the ELETTRA cavities, dedicated to SESAME, made available for Thom. X until mid-2016 (validation on the machine and then fabrication of another one, modified or not)