lcls longitudinal feedback and stability requirements p. emma llrf review november 23, 2005

P. EmmaP. Emma

LLRF MeetingLLRF Meeting [email protected]@SLAC.Stanford.edu23 Nov. 200523 Nov. 2005

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LCLSLCLS Longitudinal Feedback Longitudinal Feedback and Stability Requirementsand Stability Requirements

P. EmmaP. EmmaLLRF ReviewLLRF Review

November 23, 2005November 23, 2005

LCLSLCLS

http://www-ssrl.slac.stanford.edu/

P. EmmaP. Emma


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Critical Critical LCLSLCLS Accelerator Parameters Accelerator Parameters

Final energy 13.6 GeV (stable to Final energy 13.6 GeV (stable to 0.1%)0.1%)Final peak current 3.4 kA (stable to Final peak current 3.4 kA (stable to 12%12%))Transverse emittance 1.2 Transverse emittance 1.2 m (stable to 5%)m (stable to 5%)Final energy spread 10Final energy spread 1044 (stable to 10%) (stable to 10%)Bunch arrival time (stable to 150 fs)Bunch arrival time (stable to 150 fs)

(stability specifications quoted as rms)(stability specifications quoted as rms)


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FEL Power Sensitivity to FEL Power Sensitivity to ee Beam Beam

12% 12% IIpkpk//IIpkpk 20% 20% PP//PP

0.1% 0.1% EE//EE 0.2% 0.2% rr//rr


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Electron Bunch CompressionElectron Bunch Compression

zz

VV = = VV00sin(sin(kzkz))

RF AcceleratingRF AcceleratingVoltageVoltage

zz = = RR5656

Path-Length Energy-Path-Length Energy-Dependent BeamlineDependent Beamline

zz

ii

zz

‘‘chirp’chirp’zzii

under-under-compressioncompression

zz


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Compression StabilityCompression Stability

RF phase jitter becomes bunch length jitter…RF phase jitter becomes bunch length jitter…

Compression factor:Compression factor:

zz


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Phase and Bunch Length Stability Example (not LCLS)Phase and Bunch Length Stability Example (not LCLS)


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Machine Schematic with ParametersMachine Schematic with Parameters

SLAC linac tunnelSLAC linac tunnel research yardresearch yard

Linac-0Linac-0L L =6 m=6 m

Linac-1Linac-1L L 9 m9 m

rf rf 25°25°

Linac-2Linac-2L L 330 m330 mrf rf 41°41°

Linac-3Linac-3L L 550 m550 mrf rf 0° 0°

BC1BC1L L 6 m6 m

RR5656 39 mm39 mm

BC2BC2L L 22 m22 m

RR5656 25 mm25 mm LTULTUL L =275 m=275 mRR56 56 0 0

DL1DL1L L 12 m12 mRR56 56 0 0

undulatorundulatorL L =130 m=130 m

6 MeV6 MeVz z 0.83 mm 0.83 mm 0.05 %0.05 %

135 MeV135 MeVz z 0.83 mm 0.83 mm 0.10 %0.10 %

250 MeV250 MeVz z 0.19 mm 0.19 mm 1.6 %1.6 %

4.30 GeV4.30 GeVz z 0.022 mm 0.022 mm 0.71 %0.71 %

13.6 GeV13.6 GeVz z 0.022 mm 0.022 mm 0.01 %0.01 %

...existing linac...existing linac

223-m3-m

rfrfgungun

21-1b21-1b21-1d21-1d XX

Linac-Linac-XXL L =0.6 m=0.6 mrfrf= =

21-3b21-3b24-6d24-6d

25-1a25-1a30-8c30-8c

1 klystron1 klystron 26 klystrons26 klystrons 45 klystrons45 klystrons3 klystrons3 klystrons1 X-klys.1 X-klys.


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Correlated or Uncorrelated Errors?Correlated or Uncorrelated Errors?

Suppose the mean RF phase of all 26 Linac-2 klystrons Suppose the mean RF phase of all 26 Linac-2 klystrons changes by: changes by: 0.210.21° ° | |pkpkpkpk| | 12% 12%

This may arise statistically with 26 random uncorrelated This may arise statistically with 26 random uncorrelated phase errors with rms spread of: phase errors with rms spread of: 221/21/2 = 0.21 = 0.21°°26261/21/2 = 1.07 = 1.07°°, , oror with 26 identical phase with 26 identical phase errors.errors.

Since we don’t fully understand the correlations, we choose Since we don’t fully understand the correlations, we choose the conservative (smallest) tolerance of the conservative (smallest) tolerance of 0.21° rms/klys.0.21° rms/klys. and and then reduce this by then reduce this by ~~NN, where , where NN ( (=12=12) is the number of ) is the number of major error sources.major error sources.


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Phase, Amplitude, and Charge Phase, Amplitude, and Charge SensitivitiesSensitivities

parameterparameterEE//EE00| = | =

0.1%0.1%II//II00| = 12%| = 12% ttff| = 100 fs| = 100 fs unitunit

ttii 1.61.6 4.44.4 1.51.5 psecpsec

QQQQ00 4646 5.25.2 2424 %%

00 3.53.5 0.650.65 5.95.9 deg-Sdeg-S

VV00//VV00 0.320.32 0.240.24 0.950.95 %%

11 0.320.32 0.170.17 1.01.0 deg-Sdeg-S

VV11//VV11 0.290.29 0.250.25 0.780.78 %%

XX 5.55.5 1.41.4 7.67.6 deg-Xdeg-X

VVXX//VVXX 2.02.0 1.21.2 6.36.3 %%

22 0.540.54 0.210.21 0.0840.084 deg-Sdeg-S

VV22//VV22 1.11.1 1.01.0 0.130.13 %%

33 0.350.35 24.824.8 1515 deg-Sdeg-S

VV33//VV33 0.150.15 5.75.7 8.68.6 %%


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Longitudinal Fast-Jitter Tolerance Longitudinal Fast-Jitter Tolerance BudgetBudget

X-bandX-band XX--

0.500.50

mean phase of mean phase of 4545 klys. klys.

mean amp. of mean amp. of 4545 klys. klys.



11 X-klys. X-klys.

11 X-klys. X-klys.

11 klys. klys.

11 klys. klys.



tolerances are rms valuestolerances are rms values

laser timing (w.r.t. RF) laser timing (w.r.t. RF) laser energy laser energy


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Jitter Simulations (Particle Tracking)Jitter Simulations (Particle Tracking)

PPoutout

LLgg0.09% 0.09% 0.004% 0.004%

96 fs 96 fs

10% 10%


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LCLSLCLS LongitudinalLongitudinal Beam-Based Feedback Beam-Based Feedback

L0L0

gungun

L3L3L2L2XX

DL1DL1 BC1BC1 BC2BC2 DL2DL2L1L1

zz11

1111 VV11

zz22

2222 VV22

33

VV33

00VV00

J. Wu, et al., PAC’05, May 16-20, 2005, Knoxville, TN.J. Wu, et al., PAC’05, May 16-20, 2005, Knoxville, TN.

(stabilizes beam for jitter frequencies(stabilizes beam for jitter frequencies < 10 Hz @ 120-Hz < 10 Hz @ 120-Hz rep-rate) rep-rate)

BPMBPM

CSR detectorCSR detector


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CSR Relative Bunch Length MonitorCSR Relative Bunch Length Monitor

RedRed curve curve: : Gaussian Gaussian

BlackBlack curve curve: : UniformUniform

Blue curveBlue curve: : ‘Real’‘Real’

J. Wu, et al., PAC’05, May 16-20, 2005, Knoxville, TN.J. Wu, et al., PAC’05, May 16-20, 2005, Knoxville, TN.


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LCLS Feedback Performance (use CSR LCLS Feedback Performance (use CSR PP//PP))

J. WuJ. Wu

II pkpk

// II pkpk00 (

%)

(%)

feedback feedback onon

% 09.0/ rmsEE

% 5.10/ rmsII

ps 16.0 rmst

feedback feedback offoff

(undulator entrance)(undulator entrance)


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Feedback System Bode Plot at 120 HzFeedback System Bode Plot at 120 Hz

J. WuJ. Wu

Define fast-jitter as variations faster than Define fast-jitter as variations faster than 22 seconds secondsSlow drift occurs on time-scales > Slow drift occurs on time-scales > 22 seconds (to 24+ hr) seconds (to 24+ hr)


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Slow Drift Tolerance LimitsSlow Drift Tolerance Limits

Gun-Laser TimingGun-Laser Timing 2.4*2.4* deg-Sdeg-SBunch ChargeBunch Charge 3.23.2 %%Gun RF PhaseGun RF Phase 2.32.3 deg-Sdeg-SGun Relative VoltageGun Relative Voltage 0.60.6 %%L0,1,X,2,3 RF Phase (approx.)L0,1,X,2,3 RF Phase (approx.) 55 deg-Sdeg-SL0,1,X,2,3 RF Voltage (approx.)L0,1,X,2,3 RF Voltage (approx.) 55 %%

(Top 4 rows for (Top 4 rows for // < 5%, bottom 4 limited by feedback dynamic range) < 5%, bottom 4 limited by feedback dynamic range)

* for synchronization, this tolerance might be set to * for synchronization, this tolerance might be set to 1 ps (without arrival-time measurement)1 ps (without arrival-time measurement)

(Tolerances are peak values, not rms)(Tolerances are peak values, not rms)


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LX phase error LX phase error = 5= 5oo

L1 adjustment: phase L1 adjustment: phase 2.12.1oo, voltage , voltage 2.1%2.1%

xx (de

g)(d

eg)

x-band phasex-band phase

final energyfinal energy

final peak currentfinal peak current

final arrival timefinal arrival time

Compensate X-band Compensate X-band Phase Step Error...Phase Step Error...

J. WuJ. Wu


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Gun Gun TimingTiming Jitter and Energy Feedback Jitter and Energy Feedback

tt

EE

EE = = EE00

tt00

without energy feedbackwithout energy feedback

ttff

tt

EE

EE = = EE00

tt00

withwith energy feedback energy feedback

EE > > EE00

ttff = = tt00


lcls longitudinal feedback and stability requirements p. emma llrf review november 23, 2005

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