RF Systems for ThomX

Transcript RF Systems for ThomX

15 European Synchrotron Light Source Radio-Frequency Meeting

5 - 6 October, 2011 ESRF, Grenoble

RF systems for ThomX

P. Marchand - Synchrotron SOLEIL

The ThomX Project

Compact source of hard X-rays (40 – 90 keV) Flux of up 10 13 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 Funding of 12 M€ for Phase 1 : building of a prototype

 

Phase 2 : industrialization feasibility proof Work supported by the EQUIPEX program from the Research Ministry, Région Ile de France, CNRS-IN2P3 and University of Paris-Sud Contributions from LAL-Orsay CNRS-IN2P3, SOLEIL, CELIA Bordeaux, ESRF, C2RMF-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)

7 m

ThomX accelerator complex

SR optics : 4-fold symmetry Double Bend Achromat Interaction Region FP optical cavity

10 m Injection of a single e bunch (20 mA), which collides at each turn with laser pulses at the IP, inside the FP optical resonator



X rays from CBS



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-CTF3 gun, built by LAL E c = 100 MV/m with 10 MW Mg cathode (Q up to 1 nC) Laser :

= 266 nm , E ~ 100 µJ,

t ~ 5 ps

• •

Accelerating structure : LIL type (4.5 m long) AS, spare from SOLEIL P = 10 (20) MW

 

E = 50 (70) MeV

• • •

RF Power source : 35 MW TH 2100 klystron from Thales Solid state modulator (3 µs, 50 Hz) Power splitting : 10 MW



Gun 20 MW



• • •

Expected beam performance (PARMELA) E ~ 50 MeV (max 70)

E /E < 0.4 %

n ~ 5

mm.mrad 2.5 cell 3 GHz gun HV modulator Klystron

RF system of the Storage Ring

SR RF parameters

• •

At 50 MeV ,



U rad ~ 2 eV / turn



P beam No power to be delivered to the beam (



s RF system only generates V RF ( I b = 0) = 20 mA ) ~ 0 for suitable longit. acceptance

Selected RF frequency



500 MHz

Good compromise

V RF = 500 kV



1 single cell cavity



P RF (dis) ~ 35 kW

Availability of power sources & other RF components

Reasonable equipment size Z hom



will dictate the choice of cavity design

HOM impedances and instability thresholds



U rad ~ 0

 t

damping To preserve the beam quality ( ~ 1 s ) >>

storage



( ~ 20 ms ) Instability growth time ,

i > 20 ms Longitudinal



HOM in resonance,

i l = 2 Q s E/e / (

I o R s f m ) R s . f m (HOM) natural : 0.1 - 1 M



. GHz

 t

i l ~ 10 µs !!

Transverse



HOM in resonance,

i t = 2 E/e / (

T f rev I o R T ) R T (HOM) natural : 1 - 10 M



/ m

 t

i t ~ 10 µs !!

In both, longitudinal and transverse cases, damping of Z hom by a few 10 3 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 10 2 - 10 3 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



ELETTRA cavity with its 3 tuning means - Temperature control of f HOM



L cav (mech. deformation)

 

f o - Movable plunger on the equator

• • •

1 single cavity ~ No beam loading Small circumference Well suited to HOM tuning



Beam spectrum lines :

f = 18 MHz



HOM resonance BW : a few 10 kHz

  

f HOM R s (tuning) : a few MHz (



f = 0) / R s (



f ) = 1 + (2 Q



f / f ) 2



A few 10 3 to 10 4



Ok for ThomX Power coupler T w ± 0.1°C



L cav Plunger

HOM Spectrum

Ok Ok Ok Ok Ok

Q s I b

E o

a .

t /

l e

l = 20 ms

ELETTRA cavity L-HOM spectrum (9 modes) over the 18 MHz base band

RF power source

V RF = 500 kV, using 1 ELETTRA cavity At 500 MHz



Klystrons, IOTs,



P RF (dis) = 35 kW Solid State Amplifiers (SSA) H = 2.50 m ,



= 2 m SOLEIL technology - Well proven (6 years op.) - No HV - Modularity



redundancy - … 35 kW 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



For ThomX, make it at 500 MHz

SOLEIL - LNLS collaboration

Two amplifiers of 50 kW @ 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 kW RF plants

The two 50 kW SSA have run satisfactorily on the LNLS SR for ~ 1 year

SOLEIL R&D’s with SSA

@ 352 MHz 6 th generation transistors (V dc



At 352 MHz, P mod = 50 V) + SOLEIL expertise ~ 700 W, G > 20 dB,



[ Current LR301 mod. (V dc = 28 V) : P = 315 W, G = 13 dB,

 

> 70% fast progress = 62 % @ 352 MHz ]



Huge improvement : P mod x 2.2 , better performance (G ,



& thermal stress strongly reduced (



T : - 60 °C)



, linearity) longer lifetime



Beg. 2009, transfer of technology agreement concluded with ELTA-AREVA



ESRF contract for 7 SOLEIL type amplifiers of 150 kW (14 x 75 kW towers)



June 2010 : A 10 kW unit (16 modules) successfully tested at SOLEIL



June 2011 : First 75 kW tower passed the acceptance tests (



ESRF ) SOLEIL SSA : Evaluate 6 th generation transistors of lower power (~ 330 W) from NXP & Freescale



replace LR301 with min. modification In view of storing 500 mA using a single cryomodule :

•

Combination of two 180 kW SSA for powering one cavity

•

Input power coupler (P > 300 kW) develop t



CERN/ESRF/SOLEIL collab.

R & D’s with SSA

@ frequencies other than 352 MHz Prototypes of 500 MHz module

 

1 x 50 kW for ThomX 4 x 150 kW for SESAME : P = 650 W, G = 18 dB, η = 67 % Components design is completed



First tower : by the end of 2012 Extend the technology to frequencies from FM to L band

   

VALVO/SOLEIL



set of circulators covering the whole freq. range Prototype of 88 MHz module : P = 900 W, G = 25 dB, η ~ 80 % BBEF : 20 kW CW – 1.3 GHz SSA for the Beijing University Collab. Agreement under finalization with CERN for a prototype of 20 kW @ 200 MHz in anticipation of 2 x 1.6 MW New features :

  

Modular high efficiency 230 V _ ac / 50 V _ dc power converters Option for housing the complete SSA inside a cabinet Waveguide-to-coaxial combiner (WaCCo)



adjustable coupling



Possibility of matching variable number of modules

Waveguide-to-Coaxial Combiner (WaCCo)

2 coaxial inputs

l WG output

  

Two 6 inches coaxial input ports (2 x 80 kW)



1 WG output Replace a coaxial combiner + a coaxial-to-WG transition



Design optimization with HFSS and Microwave Studio



A 500 MHz prototype is being fabricated by BBEF Movable SC



can ensure a good matching for different configurations wit diff nb of dissipaters per tower or diff nb of modules per dissipater

ThomX LLRF system – slow loops



Compensation of slow perturbations >>

f cav = 40 µs Conventional LLRF (frequency, phase, amplitude loops)



Replica of the actual analogue SOLEIL design, adapted for 500 MHz Phase loop Amplitude loop 3dB



500 MHz Phase control

 

o PID

d 

PID



cav Voltage control + V cav Frequency tuning loop RF SWITCH Drive 40 kW AMPLIFIER Coupler RF ON / OFF Tuning control

 



cav

f CAVITY Tuner PID

Fast phase / energy oscillations

   

Injection errors,

E i ,

d

i Mismatch between injected bunch and RF bucket HOM excitations Transient beam loading (I b : 0 - 20 mA instantly) -

d

= 8° (



divided by G fbk ) - Only first injections (stationary after ~ 1 s) Oscillations in phase & energy @ f s , the synchrotron frequency with damping time,



1 /



U rad

d

( t ) t

E/E

E 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 -



t < 5 ps



/ laser



< 1° (



E / E) inj =



0.5 % (LINAC)

 

inj =



8° (AS) Still amplified by mismatch & HOM Without oscillation damping :

 

Emittance growth Bad bunch / laser overlap Loss of efficiency in the e /laser interactions @ IP

 

d s ~ 1 s >>

st = 20 ms



= 500 kHz >> BW cav ~ no natural damping during

st = 25 kHz



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 kHz) No need for additional cavity

Direct RF Feedback principle

Z(ω) P in + I g R g R s C V c I b L With FB :

At resonance (

   1  G Z

     



r ) ,

Z'  1  Z G 0

;

G   G 0 R s e  j ω Δ T BW' cav  BW cav x  1  G 0 

Gain limitation ( stability criterion )

 1  G 0  2 π ω r Q L ΔT

Loop delay Ampli-cav distance

ThomX : ampli - cavity distance ~ 10 m

 

G limit ~ 60

 

T ~ 150 ns BW ~ 1.5 MHz >> f s

Cavity transfer function with RF FB

0 -10 -20 -30 -40 -50

f r - f s f r + f s



T = 150 ns

Gain 0 Gain 44 Gain 66 -60 495,00 496,00 497,00 498,00 499,00 500,00 501,00

Frequency (MHz)

502,00 503,00 504,00 505,00 200 150 100 50 0 -50 -100 -150 -200 495,00 496,00 497,00 498,00 499,00 500,00 501,00

Frequency (MHz)

502,00 503,00 504,00 505,00 

T = 150 ns

Gain 0 Gain 44 Gain 66

RF FB + fast beam phase loop

 d

Phase comparator I b BPM 90 ° MO 500 MHz RFSwitch Driver AMPLI 50 kW 3 dB



Phase Shifter CAVITY RF FB

 

BW cav x Modulate V cav (1 + G o ) > f s at f > f s Interlocks G o RF feedback

Att 

PU cav Phase loop (BW > f s ) - Phase comparison between V c (PU cav) & I b (BPM) - The error signal,

d

(+ 90°) controls a phase shifter Alternative : Modulate the MO with

d

BW ?

Phase / energy oscillations with RF FB + fast phase loop



inj = 10 °, G o = 50, G



= 5 ,



T = 150 ns Damped after 20 µs



T _ damping = 3 µs for G



= 30 (stability limit)

Complete LLRF

MO 500 MHz 3dB

 Att

3dB RF SWITCH PA 50 kW AMPLI A Coupler CAVITY Tuner



PID PID Tuning control



Phase control Direct RF Feedback G o

Att 

PID + Beam PU Voltage control G



Conventional system with 3 « slow » loops around the cavity Frequency Amplitude Phase Oscillations @ f s



(500 kHz)



inj , HOM, … - Direct RF Feedback (G ~ 50) - Fast beam phase loop (BW > 500 kHz) Beam phase

Summary & Conclusion

RF system of ThomX SR 1) One 500 MHz ELETTRA type cavity (HOM tuning) 2) 500 kV with 35 kW, supplied by a SOLEIL type SSA 3) LLRF : conventional system with 3 slow loops (f r ,





v ) + high gain RF feedback & fast phase loop (



b ) Rem : ThomX 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 ThomX by mid-2013 - Amplifier & LLRF



designed & supplied « turn key » by SOLEIL - Cavity



one of the ELETTRA cavities, dedicated to SESAME, made available for ThomX until mid-2016 (validation on the machine and then fabrication of another one, modified or not)