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LCLS Energy Jitter Status in 2012
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  1. LCLS Energy Jitter Status in 2012 Franz-Josef Decker 24-Oct-2012 thanks to: J. Turner, R. Akre, J. Craft, A. Krasnykh, M. Nguyen, W. Colocho, … for helping to reduce jitter over the years

  2. Outline LCLS Jitter Status in 2012 • History of L1S jitter • How does a high voltage change of L1S modulator propagate • History of DL2 energy jitter (or different energies, peak currents) • Jitter is 120% (high E) to 250% (low E) of energy spread [0.04–0.12%] • What is needed for seeding • Different techniques to localize and quantify jitter

  3. L1S phase jitter over the years • 0.35 deg to 0.03 deg Un-SLEDed, HV=340kV ? Sample images BC1: E =250 MeV HV=300kV LCLS Jitter Status in 2012

  4. L1S Phase and Amplitude Calibration vs. High Voltage Phase -22 deg and Amplitude +145 MeV(BC1: E = 250 MeV)5.0 deg / % voltage change 2.5 MeV / % voltage change [expected: 5.2 deg, 1.74 MeV(sqrt 2?)] 0.1%  0.5 deg, 0.25 MeV Now at -25.5 deg, 115 MeV gives: E= 103.79 MeV 104.45 MeV +0.66 MeV [0.42 (phase) + 0.24 (ampl)]0.66/220 = 0.3% more energy in BC1 R56 = -45.5 mm  -0.468 deg in L2 -36 deg  -35.53 deg: 5 GeV  4.97 GeV-0.57 % (less energy) [R56 = -24.7 mm  +0.483 deg or 0.015 deg in L3, (L2 phase can be compensated with +18 deg in L3)] DV/V = 100 PPM (0.05 deg)  0.057% at 5 GeV LCLS Jitter Status in 2012

  5. Expected vsMeasured Slope BC2 Evs BC1 E Expected: -0.57 / 0.3 = -1.9 Measured: -0.841/0.38 = -2.210.16 corrcoef = rho LCLS Jitter Status in 2012

  6. DL2 Energy vs BC2 Energy Expected: 5 GeV / 12.3 GeV = 41% Measured: 36% / 0.744 = 48% [ = 0.044% / 0.091%] (peak current increases jitter 20%) [over-compression reduces jitter] LCLS Jitter Status in 2012

  7. Energy Jitter History at DL2 0.12 % at 3.5 GeV 3.0 times 0.04 % at 13.5 GeV 3.85 times LCLS Jitter Status in 2012

  8. Effect of Peak Current Best energy jitter 0.03 %, long bunch, high energy LCLS Jitter Status in 2012

  9. LTU WireDE/E Good: 0.033 % ‘+’ 0.040 % = 0.052 % 12.3 GeV Hard X-ray 3.5 GeV Soft X-ray Jitter 0.051 % 140 % 0.037 % = 0.063 % Jitter 0.118 % 250 % 0.046 % = 0.127 % LCLS Jitter Status in 2012

  10. How does the Energy Jitter Influence Seeding? Intensity on Direct Imager after Simulation: Jitter paints the KMONO [SASE: 0.07%] vs LTU x distribution 0.052/1.25 = 0.042% [seeded sometimes 0.030%  /2] LCLS Jitter Status in 2012

  11. Average Intensity and Variation, Seeded after KMONO 70% for 0.042% energy jitter, variation 40% rms 90% for 0.020% energy jitter, variation 10% rms 2* • 0.020% energy jitter requires DV/V = 80 PPM or 0.04 at L1S • [= 0.020/1.2*13.6/5 / 0.057 *100 PPM] LCLS Jitter Status in 2012

  12. L1S phase is still the worst offender of energy jitter [12% of jitter power at 120 Hz,] but 35% at 60 Hz But other devices are close by: 60 Hz 120 Hz L1S L1S 24-1 L0A 27-3 30-7 29-1 L0B 27-5 25-4 27-7 29-1 LCLS Jitter Status in 2012

  13. Main Causes of L1S Jitter • RF: • Multi-pacting in load and reflecting back up and DOWN • Single pulse break down (?) Both avoided by going un_SLEDed (after 220 MeV in BC1) • Modulator HV: • Thyratron not switching off “cleanly”, affecting next pulse Avoid by going to 300 kV (costs ~30 MeV, 190 MeV in BC1?) or MANY other approaches LCLS Jitter Status in 2012

  14. L1S Modulator Modifications over the Years Try to “match” modulator to klystron impedance (high micro-perveance helps) Change klystron and a few thyratrons, and ranging them Run at 300 kV instead of 340 kV Shorter PFN Tail end clipper “Mystery fan” Delay charging PFN after thyratron firing [ended in fire 120Hz] Measuring and correcting HV (ala SCALA) going on now Other ideas: capacitors with lower inductance … LCLS Jitter Status in 2012

  15. Techniques to Localize and Quantify Jitter • Methods to get data: • BSA (Beam Synchronous Acquisition) • Correlation plot • get_wf (waveforms) • L1S_jit (Jitter vs time) • Jitter CUD, FTP from matlab, • LLRFgui, KLYSTRONgui, … • Analyzing data: • BSA_jitter_fft (FFT, corrcoef, slope, …), …svd • corr_jitt … • get_wf_an14 • Plot History … LCLS Jitter Status in 2012

  16. BSA Data (Power Spectrum in DL2 Energy BPM) Feedback on: 0.054% Feedback off: 0.043 % (even with big 60 Hz component, without 0.040%) LCLS Jitter Status in 2012

  17. Correlation Plot and BSA [Transverse and FEL Intensity] BPM:IN20:371:Y is 75% correlated with VCC x position So laser causes at least 56% (=0.75^2) of 371 Y jitter (Is 42 Hz coming from laser OR MCOR power supply?)  5 Hz data From injector laser ? LCLS Jitter Status in 2012

  18. Jitter from Waveforms, e.g. L1S 300 raw waveforms, with RMS*1000 (red) revealing some elevated jitter inside the pulse, reflected signals show early multi-pacting Insert Presentation Title in Slide Master

  19. DL2 and BC1 Pie Charts Much of DL1 explained “Rest” of BC1 is big (maybe 60 Hz shows more), Laser_P is big, but gets compressed, BUT FBs sees it LCLS Jitter Status in 2012

  20. Localize Jitter vsz Concentrate on source: 16.7 Hz Make IFFT of FFT-data with only that frequency, then plot max-min vsz, fit oscillation BPM_pvs(100) = 'BPMS:BSY0:61' LCLS Jitter Status in 2012

  21. SVD for 1st BPM in DL2 L0A_A L0B_A last pulse missing, not used 60 Hz  DL2  BC2 L0B_A L0A_A L0B_A last pulse missing, not used L0A_A L0B_A MDL 476 Thales Ref Insert Presentation Title in Slide Master

  22. Summary • L1S makes ~36% of DL2 energy jitter power: • 0.6^2 + 0.8^2 = 0.36 + 0.64 = 1.0 • Energy jitter is 0.04% for hard x-ray, 0.12% for soft [0.18%] • Lowering BC1 energy to 190 MeV, might avoid current • modulator instability • Hard seeding need about 0.02%, [soft seeding ?] • Presented different methods to track down and quantify • jitter LCLS Jitter Status in 2012