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Brief Review of Method Simulations Drift Tolerances

LCLS. LCLS Undulator Alignment and Motion Review Beam-Based Alignment (BBA) Paul Emma, SLAC Oct. 21, 2005. Brief Review of Method Simulations Drift Tolerances. Motivation. For SASE FEL at 1.5 Å : Electron trajectory through undulator needs to be straight to <5 m m over ~10 m,

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Brief Review of Method Simulations Drift Tolerances

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  1. LCLS LCLS Undulator Alignment and Motion ReviewBeam-Based Alignment (BBA)Paul Emma, SLACOct. 21, 2005 • Brief Review of Method • Simulations • Drift Tolerances Paul Emma, SLAC

  2. Motivation • For SASE FEL at 1.5 Å: • Electron trajectory through undulator needs to be straight to <5 mm over ~10 m, • Traditional survey methods inadequate here, • BPM data acquired for several beam energies (14, 7.0, 4.5 GeV) can resolve this level, • Beam-based, energy-variation method is sensitive to all fields, not just misaligned quadrupole magnets Paul Emma, SLAC

  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 bi > 0 s Paul Emma, SLAC

  4. ...The Method • Reference line defined by incoming x0, x0 launch conditions mi linear only if Cij independent of p offset = -bi 1/p p (15 GeV/c)-1 (7.0 GeV/c)-1 (4.5 GeV/c)-1 Paul Emma, SLAC

  5. quads ~300 mm BPMs LINAC best final trajectory UNDULATOR (132 m) steering elements Schematic layout before BBA (cartoon example) Undulator misaligned w.r.t. linac axis with uncorrelated and correlated* (‘random walk’) component initial incoming launch error x0 x0 * suggested by C. Adolphsen Paul Emma, SLAC

  6. Final trajectory after BBA (cartoon example) Beam is launched straight down undulator, with possible inconsequential kink at boundary LINAC dispersion generated is insignificant Quadrupole magnets moved onto straight line and BPM offsets subtracted in software, while undulators track quadrupoles Paul Emma, SLAC

  7. 100 200 100 200 0.04 0.5 Input errors used for simulation Paul Emma, SLAC

  8. + Quadrupole positions  BPM offsets Initial BPM and quad misalignments (w.r.t. linac axis) quad positions BPM offsets Now launch beam through undulator Paul Emma, SLAC

  9. + Quadrupole positions e trajectory oBPM readback Initial trajectory before any correction applied ‘real’ trajectory quad positions BPM readings Paul Emma, SLAC

  10. + Quadrupole positions e trajectory oBPM readback After weighted steering – prior to BBA procedure Paul Emma, SLAC

  11. + Quadrupole positions e trajectory o BPM readback After 1st pass of BBA (13.6 GeV) sx 44 mm Dj 3322° sy 33 mm Paul Emma, SLAC

  12. Steering coils used for small, final corrections… Use steering coils for final iterations (quad move equivalent down to 0.5 mm) BPM BPM 7 mm Paul Emma, SLAC

  13. + Quadrupole positions e trajectory o BPM readback rms beam size: 36 mm After 3rd pass of BBA (13.6 GeV) sx 3.2 mm Dj 98° RON (FEL-code) simulation shows Lsat increased by <1 gain-length; R. Dejus, N.Vinokurov sy 2.5 mm Paul Emma, SLAC

  14. Run BBA on 25 Different Random Seeds 1-mm BPM resolution + 100-mm initial BPM & quad offsets x & y mover distrib. Djx,y Paul Emma, SLAC

  15. FEL code evaluation of BBA simulation results... FEL Saturation Power at 1.5 Å FEL Saturation Length at 1.5 Å B. Fawley, H.-D. Nuhn, S. Reiche, PE Paul Emma, SLAC

  16. Alignment drift during BBA procedure… • Quadrupole and BPM alignment may change during BBA procedure. • One iteration of BBA procedure will require <1 hr after full development and experience. • Simulate alignment drift during BBA, using 2.5-mm quad and BPM (separately) changes, which are uncorrelated  Paul Emma, SLAC

  17. + Quadrupole positions e trajectory o BPM readback 2.5-mm uniform quad and BPM changes during BBA procedure Dj 167° REQUIRE: < 2 mm quad/BPM stability over 1 hr Paul Emma, SLAC

  18. Allow 5-mm uniform quad and BPM drift over long term (24 hrs) 10 mm quad and BPM drift After beam-based alignment MICADO steering applied Tolerance set at 5 mm over 24 hrs Paul Emma, SLAC

  19. LCLS Summary Alignment can be achieved at adequate level using beam-based technique, given that… • BPMs resolve trajectory to 1-2 mm rms • Quad positions and BPM readings ‘drift’ <2 mm over 1-hr procedure • Trajectory is stable to <20% of beam size (already demonstrated in FFTB) • BBA procedure repeated no more than once per week given 5 mm drift tolerance Paul Emma, SLAC

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