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LCLS Longitudinal Feedback and Stability Requirements P. Emma LLRF Review November 23, 2005

LCLS. LCLS Longitudinal Feedback and Stability Requirements P. Emma LLRF Review November 23, 2005. 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 m m (stable to 5%)

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LCLS Longitudinal Feedback and Stability Requirements P. Emma LLRF Review November 23, 2005

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  1. LCLS LCLS Longitudinal Feedback and Stability Requirements P. Emma LLRF ReviewNovember 23, 2005

  2. 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)

  3. FEL Power Sensitivity to e- Beam 12% DIpk/Ipk 20% DP/P 0.1% DE/E 0.2% Dlr/lr

  4. Electron Bunch Compression d DE/E d d under-compression szi ‘chirp’ z z z sz sdi Dz = R56d V = V0sin(kz) RF Accelerating Voltage Path-Length Energy- Dependent Beamline

  5. d RF phase jitter becomes bunch length jitter… Compression factor: Df Compression Stability d z

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

  7. Machine Schematic with Parameters 250 MeV z  0.19 mm   1.6 % 4.30 GeV z  0.022 mm   0.71 % 13.6 GeV z  0.022 mm   0.01 % 6 MeV z  0.83 mm   0.05 % 135 MeV z  0.83 mm   0.10 % Linac-X L =0.6 m rf= -160 rf gun Linac-1 L 9 m rf  -25° Linac-2 L 330 m rf  -41° Linac-3 L 550 m rf  0° 23-m Linac-0 L =6 m undulator L =130 m 21-1b 21-1d 21-3b 24-6d 25-1a 30-8c X ...existing linac BC1 L 6 m R56 -39 mm BC2 L 22 m R56 -25 mm DL1 L 12 m R56 0 LTU L =275 m R56  0 1 X-klys. 3 klystrons 1 klystron 26 klystrons 45 klystrons research yard SLAC linac tunnel

  8. 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: f21/2 = 0.21°261/2 = 1.07°, or with 26 identical phaseerrors. 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.

  9. Phase, Amplitude, and Charge Sensitivities

  10. 0.50 X- X-band Longitudinal Fast-Jitter Tolerance Budget tolerances are rms values laser timing (w.r.t. RF)  laser energy  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. 

  11. Jitter Simulations (Particle Tracking) 0.09% 0.004% Lg 96 fs Pout 10%

  12. sz1 sz2 V0 d0 gun BPM d3 d1 d2 L0 1 2 V1 V2 V3 L2 L3 X L1 DL2 DL1 BC1 BC2 CSR detector LCLSLongitudinal Beam-Based Feedback (stabilizes beam for jitter frequencies < 10 Hz @ 120-Hz rep-rate) J. Wu, et al., PAC’05, May 16-20, 2005, Knoxville, TN.

  13. 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.

  14. feedback on DIpk/Ipk0 (%) LCLS Feedback Performance (use CSR P/P) feedback off J. Wu (undulator entrance)

  15. 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)

  16. Slow Drift Tolerance Limits (Top 4 rows for De/e < 5%, bottom 4 limited by feedback dynamic range) (Tolerances are peak values, not rms) * for synchronization, this tolerance might be set to 1 ps (without arrival-time measurement)

  17. Compensate X-band Phase Step Error... jx(deg) 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

  18. E E Dtf E = E0 E = E0 E > E0 Dt0 Dt0 t t Gun Timing Jitter and Energy Feedback Dtf= Dt0 without energy feedback with energy feedback

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