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LCLS Undulator Alignment and LCLS Undulator Alignment and Motion Review , Oct. 21, 2005Motion Review , Oct. 21, 2005

Paul Emma, SLACPaul Emma, [email protected]@SLAC.Stanford.edu

Linac Coherent Light Source Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

LCLS Undulator Alignment and Motion ReviewLCLS Undulator Alignment and Motion Review

Beam-Based Alignment (BBA)Beam-Based Alignment (BBA)Paul Emma, SLACPaul Emma, SLAC

Oct. 21, 2005Oct. 21, 2005

LCLS Undulator Alignment and Motion ReviewLCLS Undulator Alignment and Motion Review

Beam-Based Alignment (BBA)Beam-Based Alignment (BBA)Paul Emma, SLACPaul Emma, SLAC

Oct. 21, 2005Oct. 21, 2005

Brief Review of MethodBrief Review of Method SimulationsSimulations Drift TolerancesDrift Tolerances

Brief Review of MethodBrief Review of Method SimulationsSimulations Drift TolerancesDrift Tolerances LCLSLCLS

http://www-ssrl.slac.stanford.edu/




MotivationMotivation

For SASE FEL at 1.5 For SASE FEL at 1.5 ÅÅ::Electron trajectory through undulator needs to be straight Electron trajectory through undulator needs to be straight to <5 to <5 m over ~10 m,m over ~10 m,

Traditional survey methods inadequate here,Traditional survey methods inadequate here,

BPM data acquired for several beam energies (14, 7.0, BPM data acquired for several beam energies (14, 7.0, 4.5 GeV) can resolve this level,4.5 GeV) can resolve this level,

Beam-based, energy-variation method is sensitive to all Beam-based, energy-variation method is sensitive to all fields, not just misaligned quadrupole magnetsfields, not just misaligned quadrupole magnets

For SASE FEL at 1.5 For SASE FEL at 1.5 ÅÅ::Electron trajectory through undulator needs to be straight Electron trajectory through undulator needs to be straight to <5 to <5 m over ~10 m,m over ~10 m,

Traditional survey methods inadequate here,Traditional survey methods inadequate here,

BPM data acquired for several beam energies (14, 7.0, BPM data acquired for several beam energies (14, 7.0, 4.5 GeV) can resolve this level,4.5 GeV) can resolve this level,

Beam-based, energy-variation method is sensitive to all Beam-based, energy-variation method is sensitive to all fields, not just misaligned quadrupole magnetsfields, not just misaligned quadrupole magnets





The MethodThe Method

BPM readings, BPM readings, mmii, written as sum of upstream kicks , written as sum of upstream kicks ++ offset, offset, bbii

Kicks are sensitive to momentum, Kicks are sensitive to momentum, ppkk, while offsets, , while offsets, bbii, are not, are not

BPM readings, BPM readings, mmii, written as sum of upstream kicks , written as sum of upstream kicks ++ offset, offset, bbii

Kicks are sensitive to momentum, Kicks are sensitive to momentum, ppkk, while offsets, , while offsets, bbii, are not, are not

ss

bbii > 0 > 0

EE = 0 = 0

EE < 0 < 0quad offsets and/or pole errorsquad offsets and/or pole errors

iithth BPM BPM jj





Reference line defined by incoming Reference line defined by incoming xx00, , xx00 launch conditions launch conditionsReference line defined by incoming Reference line defined by incoming xx00, , xx00 launch conditions launch conditions

...The Method...The Method

1/1/pp

mmii

offset = bi

(15 GeV/c)(15 GeV/c)11 (7.0 GeV/c)(7.0 GeV/c)11 (4.5 GeV/c)(4.5 GeV/c)11pp

linear only if linear only if CCijij independent of independent of pp





Schematic layout before BBA (cartoon example)Schematic layout before BBA (cartoon example)

~300 ~300 mm

UNDULATORUNDULATOR(132 m)(132 m)

LINACLINACbest final trajectorybest final trajectory

steering elementssteering elements

xx00xx00

initial incoming initial incoming launch errorlaunch error

Undulator misaligned w.r.t. linac axis Undulator misaligned w.r.t. linac axis with uncorrelated and correlatedwith uncorrelated and correlated** (‘random walk’) component(‘random walk’) component

* suggested by C. Adolphsen* suggested by C. Adolphsen

BPMsBPMsquadsquads





Final trajectory after BBA (cartoon example)Final trajectory after BBA (cartoon example)

LINACLINAC

Beam is launched straight down undulator, Beam is launched straight down undulator, with possible inconsequential kink at boundarywith possible inconsequential kink at boundary

dispersion generated is insignificantdispersion generated is insignificant

Quadrupole magnets moved onto straight line and BPM offsets Quadrupole magnets moved onto straight line and BPM offsets subtracted in software, while undulators track quadrupolessubtracted in software, while undulators track quadrupoles





Input errors used for simulationInput errors used for simulation

100100

100100

0.040.04

0.50.5

200200

200200





Initial BPM and quad misalignments (w.r.t. linac axis)Initial BPM and quad misalignments (w.r.t. linac axis)

++ Quadrupole Quadrupole positionspositions BPM BPM offsetsoffsets

quad positionsquad positions

BPM offsetsBPM offsetsNow launch Now launch beam beam through through undulatorundulator





Initial trajectory before any correction appliedInitial trajectory before any correction applied

++ Quadrupole Quadrupole positionspositionsoo BPM BPM readbackreadback ee trajectory trajectory

‘‘real’ trajectoryreal’ trajectory

quad positionsquad positions BPM readingsBPM readings





After weighted steering – prior to BBA procedureAfter weighted steering – prior to BBA procedure

++ Quadrupole Quadrupole positionspositionsoo BPM BPM readbackreadback ee trajectory trajectory





After 1st pass of BBA (13.6 GeV)After 1st pass of BBA (13.6 GeV)

++ Quadrupole Quadrupole positionspositionsoo BPM readback BPM readback ee trajectory trajectory

3322°3322° 3322°3322°

xx 44 44 mmxx 44 44 mm

yy 33 33 mmyy 33 33 mm





Steering coils used for small, final corrections…Steering coils used for small, final corrections…

7 7 mm

Use steering coils for final Use steering coils for final iterations (quad move iterations (quad move

equivalent down to 0.5 equivalent down to 0.5 m)m)

Use steering coils for final Use steering coils for final iterations (quad move iterations (quad move

equivalent down to 0.5 equivalent down to 0.5 m)m)

BPM BPM





After 3rd pass of BBA (13.6 GeV)After 3rd pass of BBA (13.6 GeV)


RON RON (FEL-code) (FEL-code) simulation shows simulation shows LLsatsat increased by increased by

<1 gain-length;<1 gain-length;R. Dejus, R. Dejus, N.VinokurovN.Vinokurov

98°98° 98°98°

xx 3.2 3.2 mmxx 3.2 3.2 mm

yy 2.5 2.5 mmyy 2.5 2.5 mm rms beam size: rms beam size: 36 36 mm





Run BBA on 25 Different Random SeedsRun BBA on 25 Different Random Seeds

1-1-mm BPM BPM resolution + resolution + 100-100-mm initial initial BPM & quad BPM & quad offsetsoffsets

xx,,yyxx & & yy mover mover distrib.distrib.





FEL code evaluation of BBA simulation results...FEL code evaluation of BBA simulation results...

B. Fawley, H.-D. Nuhn, S. Reiche, PEB. Fawley, H.-D. Nuhn, S. Reiche, PE

FEL Saturation FEL Saturation Power at 1.5 Power at 1.5 ÅÅ

FEL Saturation FEL Saturation Length at 1.5 Length at 1.5 ÅÅ





Alignment drift during BBA procedure…Alignment drift during BBA procedure…

Quadrupole and BPM alignment may change Quadrupole and BPM alignment may change during BBA procedure.during BBA procedure.

One iteration of BBA procedure will require <1 hr One iteration of BBA procedure will require <1 hr after full development and experience.after full development and experience.

Simulate alignment drift during BBA, using Simulate alignment drift during BBA, using 2.5-2.5-m quad and BPM (separately) changes, which m quad and BPM (separately) changes, which are uncorrelated are uncorrelated





2.5-2.5-m uniform quad and BPM changes during BBA procedurem uniform quad and BPM changes during BBA procedure2.5-2.5-m uniform quad and BPM changes during BBA procedurem uniform quad and BPM changes during BBA procedure


167°167° 167°167°

REQUIRE:REQUIRE:< < 2 2 mm quad/BPM quad/BPM stability stability over over 1 hr1 hr





Allow Allow 5-5-m uniform quad and BPM drift over long term (24 hrs)m uniform quad and BPM drift over long term (24 hrs)Allow Allow 5-5-m uniform quad and BPM drift over long term (24 hrs)m uniform quad and BPM drift over long term (24 hrs)

After beam-based alignmentAfter beam-based alignment10 10 m quad and BPM driftm quad and BPM driftMICADO steering appliedMICADO steering applied

Tolerance set at Tolerance set at 5 5 m over 24 hrsm over 24 hrs





SummarySummary

LCLSLCLS

BPMs resolve trajectory to 1-2 BPMs resolve trajectory to 1-2 m rmsm rmsQuad positions and BPM readings ‘drift’ <2 Quad positions and BPM readings ‘drift’ <2 m over 1-hr m over 1-hr procedureprocedureTrajectory is stable to <20% of beam size (already Trajectory is stable to <20% of beam size (already demonstrated in FFTB)demonstrated in FFTB)BBA procedure repeated no more than once per week BBA procedure repeated no more than once per week given given 5 5 m drift tolerancem drift tolerance

Alignment can be achieved at adequate level Alignment can be achieved at adequate level using beam-based technique, given that…using beam-based technique, given that…


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