LCLS Longitudinal Feedback and Stability Requirements P. Emma LLRF Review November 23, 2005 LCLS 23 Nov.
Download ReportTranscript LCLS Longitudinal Feedback and Stability Requirements P. Emma LLRF Review November 23, 2005 LCLS 23 Nov.
LCLS Longitudinal Feedback and Stability Requirements P. Emma LLRF Review November 23, 2005 LCLS 23 Nov. 2005 LLRF Meeting P. Emma 1 Emma@SLAC.Stanford.edu Critical LCLS Accelerator Parameters Final energy 13.6 GeV (stable to 0.1%) Final peak current 3.4 kA (stable to 12%) Transverse emittance 1.2 mm (stable to 5%) Final energy spread 10-4 (stable to 10%) Bunch arrival time (stable to 150 fs) (stability specifications quoted as rms) 23 Nov. 2005 LLRF Meeting P. Emma 2 Emma@SLAC.Stanford.edu FEL Power Sensitivity to e- Beam 12% DIpk/Ipk 20% DP/P 0.1% DE/E 0.2% Dlr/lr 23 Nov. 2005 LLRF Meeting P. Emma 3 Emma@SLAC.Stanford.edu Electron Bunch Compression d DE/E d s zi d ‘chirp’ z z z sz sdi Dz = R56d V = V0sin(kz) RF Accelerating Voltage Path-Length EnergyDependent Beamline 23 Nov. 2005 LLRF Meeting undercompression P. Emma 4 Emma@SLAC.Stanford.edu Compression Stability d d Df z RF phase jitter becomes bunch length jitter… Compression factor: 23 Nov. 2005 LLRF Meeting P. Emma 5 Emma@SLAC.Stanford.edu Phase and Bunch Length Stability Example (not LCLS) 23 Nov. 2005 LLRF Meeting P. Emma 6 Emma@SLAC.Stanford.edu Machine Schematic with Parameters 6 MeV sz 0.83 mm sd 0.05 % 250 MeV sz 0.19 mm sd 1.6 % Linac-X L =0.6 m rf= -160 rf gun Linac-1 L 9 m rf -25° Linac-0 L =6 m 21-1b 21-1d ...existing linac DL1 L 12 m R56 0 3 klystrons 13.6 GeV sz 0.022 mm sd 0.01 % Linac-2 L 330 m rf -41° Linac-3 L 550 m rf 0° 21-3b 24-6d 25-1a 30-8c X BC1 L 6 m R56 -39 mm BC2 L 22 m R56 -25 mm 1 X-klys. 1 klystron 26 klystrons SLAC linac tunnel 23 Nov. 2005 LLRF Meeting 4.30 GeV sz 0.022 mm sd 0.71 % 135 MeV sz 0.83 mm sd 0.10 % undulator L =130 m 45 klystrons LTU L =275 m R56 0 research yard P. Emma 7 Emma@SLAC.Stanford.edu Correlated or Uncorrelated Errors? Suppose the mean RF phase of all 26 Linac-2 klystrons changes by: 0.21° |DIpk/Ipk| 12% This may arise statistically with 26 random uncorrelated phase errors with rms spread of: f21/2 = 0.21°261/2 = 1.07°, or with 26 identical phase errors. Since we don’t fully understand the correlations, we choose the conservative (smallest) tolerance of 0.21° rms/klys. and then reduce this by ~N, where N (=12) is the number of major error sources. 23 Nov. 2005 LLRF Meeting P. Emma 8 Emma@SLAC.Stanford.edu Phase, Amplitude, and Charge Sensitivities parameter |DE/E0| = 0.1% 1.6 Dti 46 DQ/Q0 3.5 Df0 0.32 DV0/V0 0.32 Df1 0.29 DV1/V1 5.5 DfX 2.0 DVX/VX 0.54 Df2 1.1 DV2/V2 0.35 Df3 0.15 DV3/V3 |DI/I0| = 12% 4.4 5.2 0.65 0.24 0.17 0.25 1.4 1.2 0.21 1.0 24.8 5.7 23 Nov. 2005 LLRF Meeting |Dtf| = 100 fs 1.5 24 5.9 0.95 1.0 0.78 7.6 6.3 0.084 0.13 15 8.6 unit psec % deg-S % deg-S % deg-X % deg-S % deg-S % P. Emma 9 Emma@SLAC.Stanford.edu Longitudinal Fast-Jitter Tolerance Budget tolerances are rms values laser timing (w.r.t. RF) laser energy 0.50 mean phase of 2 klys. 1 klys. 1 X-klys. mean phase of 26 klys. mean phase of 45 klys. mean amp. of 2 klys. 1 klys. 1 X-klys. mean amp. of 26 klys. mean amp. of 45 klys. 23 Nov. 2005 LLRF Meeting X- X-band P. Emma 10 Emma@SLAC.Stanford.edu Jitter Simulations (Particle Tracking) 0.09% 0.004% Lg 96 fs Pout 10% 23 Nov. 2005 LLRF Meeting P. Emma 11 Emma@SLAC.Stanford.edu LCLS Longitudinal Beam-Based Feedback (stabilizes beam for jitter frequencies < 10 Hz @ 120-Hz rep-rate) gun V0 s z1 d0 d1 1 V1 L1 DL1 BPM 2 V2 s z2 d2 L2 X BC1 d3 V3 L3 BC2 DL2 CSR detector J. Wu, et al., PAC’05, May 16-20, 2005, Knoxville, TN. 23 Nov. 2005 LLRF Meeting P. Emma 12 Emma@SLAC.Stanford.edu CSR Relative Bunch Length Monitor Red curve: Gaussian Black curve: Uniform Blue curve: ‘Real’ J. Wu, et al., PAC’05, May 16-20, 2005, Knoxville, TN. 23 Nov. 2005 LLRF Meeting P. Emma 13 Emma@SLAC.Stanford.edu LCLS Feedback Performance (use CSR DP/P) feedback off feedback on DIpk/Ipk0 (%) DE / E rms 0.09 % DI / I rms 10.5 % Dt rms 0.16 ps J. Wu (undulator entrance) 23 Nov. 2005 LLRF Meeting P. Emma 14 Emma@SLAC.Stanford.edu Feedback System Bode Plot at 120 Hz J. Wu Define fast-jitter as variations faster than 2 seconds Slow drift occurs on time-scales > 2 seconds (to 24+ hr) 23 Nov. 2005 LLRF Meeting P. Emma 15 Emma@SLAC.Stanford.edu Slow Drift Tolerance Limits (Top 4 rows for De/e < 5%, bottom 4 limited by feedback dynamic range) Gun-Laser Timing Bunch Charge Gun RF Phase Gun Relative Voltage L0,1,X,2,3 RF Phase (approx.) L0,1,X,2,3 RF Voltage (approx.) 2.4* deg-S 3.2 % 2.3 deg-S 0.6 % 5 deg-S 5 % (Tolerances are peak values, not rms) * for synchronization, this tolerance might be set to 1 ps (without arrival-time measurement) 23 Nov. 2005 LLRF Meeting P. Emma 16 Emma@SLAC.Stanford.edu x (deg) Compensate X-band Phase Step Error... x-band phase LX phase error = 5o final energy final peak current L1 adjustment: phase +2.1o, voltage -2.1% final arrival time J. Wu 23 Nov. 2005 LLRF Meeting P. Emma 17 Emma@SLAC.Stanford.edu Gun Timing Jitter and Energy Feedback E E Dtf E > E0 E = E0 Dt0 without energy feedback E = E0 t 23 Nov. 2005 LLRF Meeting Dt0 Dtf = Dt0 with energy feedback P. Emma 18 Emma@SLAC.Stanford.edu t