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LCLS Linac Tuning Simulations P. Emma LCLS Week April 5, 2005

LCLS. LCLS Linac Tuning Simulations P. Emma LCLS Week April 5, 2005. Thanks to M. Borland for Elegant code changes in support of these studies. Description of the Study. Start with low-charge configuration (0.2 nC, no CSR) Use elegant to automate tuning; use only ‘real’ diagnostics

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LCLS Linac Tuning Simulations P. Emma LCLS Week April 5, 2005

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  1. LCLS LCLS LinacTuning Simulations P. Emma LCLS Week April 5, 2005 Thanks to M. Borland for Elegant code changes in support of these studies

  2. Description of the Study • Start with low-charge configuration (0.2 nC, no CSR) • Use elegant to automate tuning; use only ‘real’ diagnostics • Add large random errors to linac systems (e.g., magnets, RF, beam) • Assume rough corrections already made (see LCLS Commissioning Workshop, Sep. 2004) • Track through linac many times, each step simulating one particular correction (e.g., b-matching or RF phasing) • Use correction devices already built into design (e.g., BC2 correction quads, trajectory controls) • Evaluate final beam quality, correction convergence, dynamic range, problem areas, etc.

  3. Linac System Errors

  4. Sequential Corrections Applied in Simulations • Steer entire machine (initially ignore BPMs in DL1, BC1, BC2) • Set energy and minimize spread in DL1 (OTR4, BPM13 and L0b phase/voltage) • Set energy and bunch length after BC1 (BPMS11, transverse deflector-BC2-off, L1 phase/voltage) • Set energy and bunch length after BC2 (BPMS21, transverse deflector, L2 phase/voltage) • Beta-match injector (OTR1-3, QA01-2, QE01-4) • Correct trajectory again to compensate quad steering • Minimize gey after BC1 with trajectory in QM12 (WS11-13, YC21201) • Minimize gey after BC2 with L2 trajectory (WS21-24, YCM12, YC21601) • Minimize gex after BC2 with L2 trajectory (WS21-24, XCM11, XCM13) • Correct hx and hx after BC2 (WS044-544, CQ21, CQ22) • Minimize gex at end of LTU with ‘bumps’ (WS31-4, XC460026, XC6) • Match b after BC2 & LTU (WS044-544, Q24701, WS31-4, Q6, QEM3)

  5. Trajectory After First Steering BC2 DL1 BC1

  6. Projected Emittance After First Steering Q = 0.2 nC

  7. b-mismatch amplitude after first steering zx = 3.3 ! GOAL = 1

  8. Final Long. Phase Space After First Steering sz = 8.6 mm (0.2-nC design is 8.0 mm) (NOT BAD) DE/E0 = -0.3%

  9. L0 L1 L2 L3 X Set Energy and Minimize Spread in DL1 (OTR4) minimize OTR4 x-spot size while scanning L0b RF phase long. DL1 phase space before long. DL1 phase space after OTR4 after OTR4 before

  10. L0 L1 L2 L3 X Set energy and bunch length after BC1 post-BC1 long.phase space before post-BC1 long.phase space after sz = 43 mm sz = 55 mm design: 60 mm Sec-25 transverse deflector (BC2 off)  meas. post-BC1 bunch length BC1 BPM  meas. BC1 rel. energy L1 RF phase adjust bunch length to ~60 mm L1 RF amplitude adjust BC1 BPM to x = 0  0.25 mm

  11. L0 L1 L2 L3 X Set energy and bunch length after BC2 post-BC2 long. phase space before post-BC2 long.phase space after sz = 12 mm sz = 8.7 mm DE/E0 = +0.8% design: 8.0 mm sec-25 transverse deflector (BC2 on)  meas. post-BC2 bunch length BC2 BPM  meas. BC2 energy L2 RF phase adjust bunch length to 8.0 mm L2 RF amplitude adjust BC2 BPM to x = 0  0.25 mm

  12. Trajectory After BC1/BC2 Energy Corrections

  13. L0 L1 L2 L3 X b-match at OTR2 in the Injector L0b QA01-02, QE01-04 OTR3 OTR2 OTR1

  14. L0 L1 L2 L3 X b-match at OTR2 with quads: QA01-2, QE01-4 sx = 67.5 mm sx = 57.9 mm before correction after correction sy = 76.1 mm sy = 61.2 mm

  15. L0 L1 L2 L3 X Measure Emittance on OTR11-13 after BC1 OTR13 OTR12 OTR11 OTR2

  16. L0 L1 L2 L3 X Vertical offset in QM12 can be trouble y OTR12 x gey gex

  17. L0 L1 L2 L3 X Minimize gey on OTR12 using YC21201 x y gex gey

  18. L0 L1 L2 L3 X Minimize gey at WS21 with YCM12 & YC21601 BC2 gex gey

  19. L0 L1 L2 L3 X Now Repeat for gex on WS21 (XCM11 & XCM13) BC2 gex gey

  20. L0 L1 L2 L3 X Correct Dispersion in BC2 (WS044 and CQ21, CQ22) BC2 gey gex

  21. L0 L1 L2 L3 X Tweak LTU traj. to minimize gex on WS31-4 XC460026 XC6 BC2 gey gex

  22. b-match needs correction after BC2 and in LTU Wow! (zx = 3.3) GOAL = 1

  23. After b-matching at WS044 and WS31 Q24701 Q6 QEM3 zx= 4 ? z 1 hand tweaked, much like real machine

  24. Emittance After Final b-matching (no CSR) gey= 0.91 mm gex = 0.88 mm

  25. Final Longitudinal Phase Space (no CSR) DESIGN DESIGN DESIGN TUNEUP TUNEUP TUNEUP 2 kA

  26. Final Slice Emittance (no CSR) limit at 0.2 nC, 2 kA Slice emittance originates from Parmela run at 0.2 nC, 35 A (C. Limborg)

  27. Final Slice Energy Spread (no CSR) limit at 0.2 nC, 2 kA Slice energy spread originates from laser-heater (set a bit low here)

  28. Summary • Tuning results look encouraging (at 0.2 nC) • Steering (Dy) after BC1 can be very important • Setting energy accurately in BC2 needs work • Beta-matching through LTU may benefit from additional e-diagnostics between DL2 bend pairs • Limited resolution of diagnostics not included (they must meet specifications) • BC2 off to meas. BC1 sz is clumsy (3rd T-cav?) • Should add CSR (but very slow) LCLS

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