1 / 28

BBA Related Issues Heinz-Dieter Nuhn, SLAC / LCLS June 28, 2004

LCLS. BBA Related Issues Heinz-Dieter Nuhn, SLAC / LCLS June 28, 2004. Technique Simulations Earth Field Considerations. LCLS. Basic Strategy. Save BPM readings as a function of large, deliberate changes in e - energy (e.g., 14, 7, and 5 GeV).

honorato-berger
Download Presentation

BBA Related Issues Heinz-Dieter Nuhn, SLAC / LCLS June 28, 2004

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. LCLS BBA Related IssuesHeinz-Dieter Nuhn, SLAC / LCLSJune 28, 2004 • Technique • Simulations • Earth Field Considerations Heinz-Dieter Nuhn, SLAC / LCLS

  2. LCLS Basic Strategy • Save BPM readings as a function of large, deliberate changes in e- energy (e.g., 14, 7, and 5 GeV) • Calculate and correct quad & BPM misalignments and adjust ‘launch’ • Repeat ~3 times with first application • Re-apply one iteration per ~1 month (?) Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of Paul Emma

  3. j ith BPM DE = 0 quad offsets and/or pole errors DE < 0 The Method • BPM readings, mi, written as sum of upstream kicks + offset, bi • Kicks are sensitive to momentum, pk, while offsets, bi, are not • Reference line defined by incoming x0, x0 launch conditions bi > 0 s Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of Paul Emma

  4. The Method • Extrapolation to infinite momentum give BPM offsets mi linear only if Cij independent of p offset = -bi 1/p p (15 GeV/c)-1 (10 GeV/c)-1 (5 GeV/c)-1 Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of Paul Emma

  5. The Method • Define… • then solve the linear system… BPM readings at p1 BPM offsets BPM readings at p2 quad offsets known optical functions at each pk Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of Paul Emma

  6. ~1 mm Constraints • Solve with ‘soft-constraints’* on resulting BPM and quad offsets • Without this ‘reasonability’ weighting, resulting BPM and quad offsets can stray out to large values at low frequencies • Scanning beam energy gives sensitivity to (and ~correction of) all field errors, including undulator poles, Earth’s field, etc… * C. Adolphsen, 1989 PAC Heinz-Dieter Nuhn, SLAC / LCLS Courtesy of Paul Emma

  7. quads ~300 mm BPMs LTU best final trajectory UNDULATOR (120 m) steering elements Schematic layout Courtesy of Paul Emma Undulator misaligned w.r.t. linac axis with uncorrelated and correlated* (‘random walk’) component original incoming launch error x0 x0 130 permanent magnet quadrupoles and undulator poles * suggested by C. Adolphsen Heinz-Dieter Nuhn, SLAC / LCLS

  8. Beam-based alignment steps Courtesy of Paul Emma ×3 Heinz-Dieter Nuhn, SLAC / LCLS

  9. Input Errors Used for Simulation Courtesy of Paul Emma 2 100 100 0.04 4 Heinz-Dieter Nuhn, SLAC / LCLS

  10. + Quadrupole positions quad positions o BPM offsets BPM offsets Initial BPM and quad misalignments (w.r.t. linac axis) Courtesy of Paul Emma Now launch beam through undulator 130 130 Heinz-Dieter Nuhn, SLAC / LCLS

  11. + Quadrupole positions e trajectory ‘real’ trajectory o BPM readback quad positions fit used to smooth launch BPM readings Initial trajectory before any correction applied Courtesy of Paul Emma Note, all trajectory plots are w.r.t. linac axis (except last two) 130 130 Heinz-Dieter Nuhn, SLAC / LCLS

  12. + Quadrupole positions e trajectory o BPM readback Trajectory after initial rough steering (14.3 GeV) Courtesy of Paul Emma Save as 1st set of BPM readings 130 130 Heinz-Dieter Nuhn, SLAC / LCLS

  13. + Quadrupole positions e trajectory o BPM readback Energy now reduced to 10 GeV Courtesy of Paul Emma Save as 2nd set of BPM readings 130 130 Heinz-Dieter Nuhn, SLAC / LCLS

  14. + Quadrupole positions e trajectory o BPM readback Energy reduced again to 5 GeV Courtesy of Paul Emma Save as 3rd set of BPM readings Now analyze BPM data… 130 130 Heinz-Dieter Nuhn, SLAC / LCLS

  15. Fit results Actual offsets ‘real’ offsets fitted offsets Fitted quadrupole offsets Courtesy of Paul Emma results differ by straight line… similar plot for BPM offsets (not shown) Now correct quad and BPM positions… 130 use linear component of fitted offsets to re-adjust launch 130 Heinz-Dieter Nuhn, SLAC / LCLS

  16. + Quadrupole positions e trajectory o BPM readback Absolute trajectory after 1st pass of BBA (14.3 GeV) Courtesy of Paul Emma 130 130 Heinz-Dieter Nuhn, SLAC / LCLS

  17. Possible Absolute Trajectory Courtesy of Paul Emma Beam is launched straight down undulator, with possible inconsequential kink at boundary LTU dispersion generated is insignificant Now look at trajectory w.r.t. undulator axis  Heinz-Dieter Nuhn, SLAC / LCLS

  18. + Quadrupole positions e trajectory o BPM readback After 1st pass of BBA (now w.r.t. undulator line) Courtesy of Paul Emma sx 48 mm Now repeat procedure of energy changes two more times… 130 sy 24 mm 130 Heinz-Dieter Nuhn, SLAC / LCLS

  19. + Quadrupole positions e trajectory o BPM readback rms beam size: 30 mm After 3rd pass of BBA (14.3 GeV) Courtesy of Paul Emma sx 1.7 mm Dj 100° 130 RON (FEL-code) simulation shows Lsat increased by <1 gain-length; R. Dejus, N.Vinokurov sy 2.7 mm 130 Was confirmed with GENESIS simulation Heinz-Dieter Nuhn, SLAC / LCLS

  20. + Quadrupole positions e trajectory o BPM readback Trajectory After BBA Convergence Courtesy of Paul Emma • 2-mm BPM resolution • 50-mm initial BPM & quad offsets • 1-mm mover backlash • 14-7-4.5 GeV • Dj204° Trajectory through undulator at 14 GeV after 3 passes of BBA procedure. Heinz-Dieter Nuhn, SLAC / LCLS

  21. Verify BBA Convergence by noting orbit change from 14 to 4.5 GeV Before BBA procedure 14.1 GeV Courtesy of Paul Emma drop energy, reset launch, note change 4.5 GeV 500 mm BPM read-backs through undulator at 14 GeV (top) and 4.5 GeV (bottom) after rough steering, but before the BBA procedure. The energy is changed and the launch is re-established. Trajectory changes are expected at the 500-mm level. Heinz-Dieter Nuhn, SLAC / LCLS

  22. Verifying BBA Convergence After BBA procedure 14.1 GeV Courtesy of Paul Emma drop energy, reset launch, note change 4.5 GeV 20 mm BPM read-backs through undulator (note scale change) at 14 GeV (top) and 4.5 GeV (bottom) after three rounds of the BBA procedure, where trajectory changes with energy are expected at the 20-mm level. Heinz-Dieter Nuhn, SLAC / LCLS

  23. 0.1-Gauss Earth’s field in x- direction – perfect system, quads on, no steering Courtesy of Paul Emma Heinz-Dieter Nuhn, SLAC / LCLS

  24. Courtesy of Paul Emma 0.1-Gauss Earth’s field in x-direction – perfect system, after BBA Heinz-Dieter Nuhn, SLAC / LCLS

  25. 0.1-Gauss Earth’s field in x-direction – standard errors, after BBA Courtesy of Paul Emma no Earth’s field – standard errors, after BBA Heinz-Dieter Nuhn, SLAC / LCLS

  26. 0.2-Gauss Earth’s field in x-direction – standard errors, after BBA Courtesy of Paul Emma Heinz-Dieter Nuhn, SLAC / LCLS

  27. LCLS Summary • BPMs resolve trajectory to ~1 mm rms • BPM readings ‘drift’ <1 mm over 1-2 hr (temperature) • Magnet movers are settable to within 1 mm (or use coils) • BPM readings are not sensitive to variable beam size, etc. • Trajectory is stable enough to <20% of beam size (already demonstrated in FFTB) • Earth magnetic field needs to be compensated Alignment can be achieved at adequate level using beam-based technique, given that… 4 Heinz-Dieter Nuhn, SLAC / LCLS

  28. End of Presentation Heinz-Dieter Nuhn, SLAC / LCLS

More Related