undulator physics april 29, 2004 heinz-dieter nuhn, slac / ssrl facility advisory committee meeting...

Undulator Physics April 29, 2004 Heinz-Dieter Nuhn, SLAC / SSRLFacility Advisory Committee Meeting [email protected]@slac.stanford.edu

Undulator PhysicsDiagnostics / Commissioning Strategy

Heinz-Dieter Nuhn, SLAC / SSRLApril 29, 2004

Undulator PhysicsDiagnostics / Commissioning Strategy

Heinz-Dieter Nuhn, SLAC / SSRLApril 29, 2004

Undulator Overview FEL Parameters Diagnostics and Commissioning Strategy

Undulator Overview FEL Parameters Diagnostics and Commissioning Strategy


Linac Coherent Light Source

Near Hall

Far Hall

Undulator


Undulator Segment Prototype


Undulator Type planar hybridMagnet Material NdFeBWiggle Plane horizontalGap 6.5 mmPeriod Length 3.0 ± 0.003 cmEffective On-Axis Field 1.296 TEffective Undulator Parameter K 3.630 ± 0.015 %Segment Phase Slippage Tolerance 10

degrees

Module Length 3.40 mNumber of Modules 33Undulator Magnet Length 112.2 m

Standard Break Lengths 49.6 - 49.6 - 72.3 cmTotal Device Length 130.4 m

Lattice Type FODOMagnet Type permanentNominal Magnet Length 5 cmQF Gradient 60 T/mQD Gradient -60 T/mAverage Function at 1.5 Å (14.08 GeV) 30 mAverage Function at 15. Å (4.45 GeV) 8.9 mLowest Usable Energy 1.84 GeV

Undulator Type planar hybridMagnet Material NdFeBWiggle Plane horizontalGap 6.5 mmPeriod Length 3.0 ± 0.003 cmEffective On-Axis Field 1.296 TEffective Undulator Parameter K 3.630 ± 0.015 %Segment Phase Slippage Tolerance 10

degrees

Module Length 3.40 mNumber of Modules 33Undulator Magnet Length 112.2 m

Standard Break Lengths 49.6 - 49.6 - 72.3 cmTotal Device Length 130.4 m

Lattice Type FODOMagnet Type permanentNominal Magnet Length 5 cmQF Gradient 60 T/mQD Gradient -60 T/mAverage Function at 1.5 Å (14.08 GeV) 30 mAverage Function at 15. Å (4.45 GeV) 8.9 mLowest Usable Energy 1.84 GeV

Summary of Nominal Undulator ParametersSummary of Nominal Undulator Parameters


Beam Based Alignment Tolerances (Paul Emma)Beam Based Alignment Tolerances (Paul Emma)


FEL SimulationsFEL Simulations

Parameter Range

Wavelength

Charg

e

15 Å1.5 Å

0.2 nC

1.0 nCstrong wakefields

loss

es

due t

osp

on.

rad.

deep s

atu

rati

on

Operation Space

Energy 14.1 GeV 4.4 GeV

Current 3.4 kA 3.4 kA

Charge 0.2 - 1 nC 0.2 - 1 nC

Slice Emittance 1.2 mm mrad 1.2 mm mrad

Slice Energy Spread 0.01 % 0.025 %

Undulator Period 3 cm 3 cm

Undulator Parameter 3.63 3.63

-function 18 m 7.5 m

Wavelength 1.5 Å 15 ÅLowering the charge reduces bunch

length, current and emittance

ParmelaParmelaParmelaParmela ElegantElegantElegantElegant GenesisGenesisGenesisGenesis

space-chargespace-charge compression, wakes, CSR, …compression, wakes, CSR, … SASE FEL with wakesSASE FEL with wakes

Start-To-End Simulations:Start-To-End Simulations:


Expected PerformanceExpected Performance

Low charge cases are modeled in PARMELAafter the GTF results and then imported into ELEGANT/GENESIS for the transport through

the LCLS beam line. The simulations includes:

Space charge in the gun

Emittance compensation

Wakefield and CSR effects

Optimized beam transport (Jitter)

Spontaneous Undulator Radiation

All cases reach saturationAll cases reach saturation


Risk Assessment: Undulator LengthRisk Assessment: Undulator Length

Saturation predicted 40 m before undulator end

Space for Undulator Extension Available if needed.

Saturation predicted 40 m before undulator end

Space for Undulator Extension Available if needed.

Length of Undulator Hall 175 m

Length of Undulator 130 m

Length of Undulator Hall 175 m

Length of Undulator 130 m

Available Undulator

Length

Available Undulator

Length

Extendable Undulator

Length

Extendable Undulator

Length

Nominal Working Point

Nominal Working Point

1.7 mm mrad

1.7 mm mrad

1.2 mm mrad

1.2 mm mrad


Diagnostics and Commissioning WorkshopDiagnostics and Commissioning Workshop

LCLS Diagnostics and Commissioning Workshop

Dates

January 19-20, 2004

LocationUCLA, Los Angeles, USA

http://ssrl.slac.stanford.edu/lcls/undulator/meetings/2004-01-19_diagnostics_comissioning/Workshop Website

http://www-ssrl.slac.stanford.edu/lcls/technotes/lcls-tn-04-2.pdf

http://www.slac.stanford.edu/pubs/slacreports/slac-r-715.html

Workshop Report


GoalsGoals

End-Of-Construction Goal

Defined by DOE to close-off construction project (CD-4)

One of the first Commissioning Milestones

Commissioning Goal

Get LCLS ready for operation

End-Of-Construction Goal

Defined by DOE to close-off construction project (CD-4)

One of the first Commissioning Milestones

Commissioning Goal

Get LCLS ready for operation


FEL CommissioningFEL Commissioning

Scope

Commissioning of the FEL Undulator with Beam

Prerequisites

Undulator, Diagnostics, Shielding, Beam Dump etc. in Place

Commissioning Without Beam for all Components Complete

Main Commissioning Tasks

Characterization of Electron Beam Up-Stream of Undulator

Establishment of a Good Beam Trajectory Through Undulator to Beam-Dump

Characterization of Spontaneous Radiation

Establishment of SASE Gain

Characterization of FEL Radiation

Scope

Commissioning of the FEL Undulator with Beam

Prerequisites

Undulator, Diagnostics, Shielding, Beam Dump etc. in Place

Commissioning Without Beam for all Components Complete

Main Commissioning Tasks

Characterization of Electron Beam Up-Stream of Undulator

Establishment of a Good Beam Trajectory Through Undulator to Beam-Dump

Characterization of Spontaneous Radiation

Establishment of SASE Gain

Characterization of FEL Radiation

Low Charge, Single ShotLow Charge, Single Shot

Low Charge, 10 HzLow Charge, 10 Hz

10 Hz10 Hz


IssuesIssues

Undulator Radiation Protection

Measurements of FEL Radiation vs. Z

Radiation Power Damage to Inter Undulator X-Ray Diagnostics

End-of-Undulator Diagnostics

Beam Based Detection of Gain Reducing Errors

Using Spontaneous Radiation

Using FEL Gain Curve

Numerical Simulation Support for Detector Development and Commissioning

Undulator Radiation Protection

Measurements of FEL Radiation vs. Z

Radiation Power Damage to Inter Undulator X-Ray Diagnostics

End-of-Undulator Diagnostics

Beam Based Detection of Gain Reducing Errors

Using Spontaneous Radiation

Using FEL Gain Curve

Numerical Simulation Support for Detector Development and Commissioning


/2/2 /2/2

xx11 xx22 xx33

phase-1phase-1 phase-2phase-2 phase-1 phase-1 againagain

halohalo

ee beam beam

3 mm mm

2 mm2 mm

Two-Phase, Two-Plane Collimation, 1½ TimesTwo-Phase, Two-Plane Collimation, 1½ Times

undulator undulator beam beam pipepipe

2.5 mm5 mmedge edge scatteringscattering

(also collimation in (also collimation in yy and energy – see next slides) and energy – see next slides)Courtesy of P. EmmaCourtesy of P. Emma

UndulatorUndulator Radiation Protection


EE11 EE

22

xx11yy11 xx22

yy22xx33yy33

LCLS Collimation Proposal (2 energy, 3 LCLS Collimation Proposal (2 energy, 3 xx, and 3 , and 3 yy adjustable collimators) adjustable collimators)muon muon

shieldinshieldingg

undulatoundulatorr

xx33 & & yy33

optional?optional?

Courtesy of P. EmmaCourtesy of P. Emma


22ndnd-order -order tracking with all tracking with all collimators collimators closed and big closed and big halohalo

2.5 mm2.5 mm

2-phase, 2-plane, and energy collimation in 22-phase, 2-plane, and energy collimation in 2ndnd-order-order

well well shadowed in shadowed in xx, , yy, and , and EE

?-CY3-?CX3

2.0-CY2-2.0CX2

2.0-CY1-2.0CX1-5.0CE2-5.0CE1

ymm

xmmColl.

xx,,yy = 4000 = 4000 m,m,

EE//EE = 10% (uniform) = 10% (uniform)Courtesy of P. EmmaCourtesy of P. Emma


Trajectory through undulator at 14 GeV after 3 passes of BBA procedure.Trajectory through undulator at 14 GeV after 3 passes of BBA procedure.

Trajectory After BBA ConvergenceTrajectory After BBA Convergence

2-2-mm BPM BPM resolutionresolution50-50-mm initial BPM & initial BPM & quad offsetsquad offsets1-1-mm mover mover backlashbacklash14-7-4.514-7-4.5 GeV GeV 204°204°

2-2-mm BPM BPM resolutionresolution50-50-mm initial BPM & initial BPM & quad offsetsquad offsets1-1-mm mover mover backlashbacklash14-7-4.514-7-4.5 GeV GeV 204°204°

++ Quadrupole Quadrupole positionspositions

oo BPM readback BPM readback

ee trajectory trajectory



BPM read-backs through undulator at 14 GeV (top) and 4.5 BPM read-backs through undulator at 14 GeV (top) and 4.5 GeV (bottom) after rough steering, but before the BBA GeV (bottom) after rough steering, but before the BBA procedure. The energy is changed and the launch is re-procedure. The energy is changed and the launch is re-established. Trajectory changes are expected at the established. Trajectory changes are expected at the 500-500-mm level.level.

500 500 mm

Verify BBA Convergence by noting orbit change from 14 to 4.5 GeVVerify BBA Convergence by noting orbit change from 14 to 4.5 GeVBeforeBefore BBA procedure BBA procedure

14.1 GeV14.1 GeV

4.5 GeV4.5 GeV

drop energy, drop energy, reset launch, reset launch, note changenote change



BPM read-backs through undulator (note scale change) at 14 GeV BPM read-backs through undulator (note scale change) at 14 GeV (top) and 4.5 GeV (bottom) after three rounds of the BBA procedure, (top) and 4.5 GeV (bottom) after three rounds of the BBA procedure, where trajectory changes with energy are expected at the where trajectory changes with energy are expected at the 20-20-mm level.level.

20 20 mm

Verifying BBA ConvergenceVerifying BBA ConvergenceAfterAfter BBA procedure BBA procedure

drop energy, drop energy, reset launch, reset launch, note changenote change

14.1 GeV14.1 GeV

4.5 GeV4.5 GeV



GG = 110 T/m = 110 T/mTrack 100 times with:Track 100 times with:

DL2 BPM rms res. = 10 DL2 BPM rms res. = 10 mmDL2 BPM rms misa. = 200 DL2 BPM rms misa. = 200 mmDL2 Quad rms misa. = 200 DL2 Quad rms misa. = 200 mmUndulator Quad rms misa. = 100 Undulator Quad rms misa. = 100 mm

Correct und-launch, then open stopper-2 for one beam shot…Correct und-launch, then open stopper-2 for one beam shot…

Just Just 11 of 10011 of 100 trajectories exceed trajectories exceed 2.5 mm within undulator2.5 mm within undulatorNoneNone exceed exceed 3.5 mm3.5 mm

First beam shot First beam shot through through undulator?undulator?



Desirable measurements as function of position along undulator :

Intensity (LG, Saturation)

Spectral Distribution

Bunching

Desirable measurements as function of position along undulator :

Intensity (LG, Saturation)

Spectral Distribution

Bunching

FEL Gain MeasurementFEL Gain Measurement

Undulator RegimeUndulator Regime

Exponential Gain Regime

Exponential Gain Regime

Saturation

Saturation

1 % of X-Ray Pulse1 % of X-Ray Pulse

Electron BunchMicro-Bunching

Electron BunchMicro-Bunching


Dose / Power ConsiderationsDose / Power Considerations

0.01

0.1

1

10

100

100 1000 10000

Photon energy (eV)

Flu

en

ce (

J/cm

^2

)

undulatorexitexperimentalhall A

experimentalhall B

C

Si

W

Au

Be

0.01

0.1

1

10

0.1 1 10 100

grazing angle (degrees)

energ

y d

ensit

y c

orr

ect

ion

0.8 keV critical angle

0.8 keV

8 keV critical angle

8 keV

with electroncorrection

no electroncorrection

Fluence to Melt

Energy Density Reduction of a

Reflector

Be will melt at normal incidence at E < 3 KeV near undulator exit.

Using Be as a grazing incidence reflector may gain x 10 in tolerance.

Courtesy of R. BiontaCourtesy of R. Bionta


End-of-Undulator Commissioning DiagnosticsEnd-of-Undulator Commissioning Diagnostics

MeasurementsTotal energy

Pulse length

Photon energy spectra

Spatial coherence

Spatial shape and centroid

Divergence

MeasurementsTotal energy

Pulse length

Photon energy spectra

Spatial coherence

Spatial shape and centroid

Divergence


Fastclosevalve

Slit A

PPS

13'Muonshield

Gas Attenuator

SolidAttenuator

Slit B

PPS

4'Muonshield

WindowlessIonChamber

Direct ImagerIndirect Imager

Spectrometer,Total Energy

PPS

AccessShaft

AccessShaft

Courtesy of R. BiontaCourtesy of R. Bionta


Measurement of SASE Gain along the undulatorMeasurement of SASE Gain along the undulator

Direct: Detectors in the Breaks between Undulator Segments.

No good solution for x-ray detector in existence, yet.

Alternative: Characterize x-ray beam at single station down stream of undulator after gain is turned off at a selectable point along undulator by

introduction of orbit distortion. (Initial studies by Z. Huang)

removal of undulator segments (Changed Design)

opening of gap if undulator is variable gap device. (Changed Design)

Direct: Detectors in the Breaks between Undulator Segments.

No good solution for x-ray detector in existence, yet.

Alternative: Characterize x-ray beam at single station down stream of undulator after gain is turned off at a selectable point along undulator by

introduction of orbit distortion. (Initial studies by Z. Huang)

removal of undulator segments (Changed Design)

opening of gap if undulator is variable gap device. (Changed Design)


Measurement of SASE Gain withMeasurement of SASE Gain withend-of-undulator diagnosticsend-of-undulator diagnostics

GENESIS Simulations by Z. Huang


Spontaneous vs. FEL RadiationSpontaneous vs. FEL Radiation -1--1-

Figure by S. ReicheFigure by S. Reiche


Spontaneous vs. FEL Radiation Spontaneous vs. FEL Radiation -2--2-



Startup at 15 Startup at 15 ÅÅ with highly degraded with highly degraded ee beam quality beam quality

FEL gain highly likely in initial commissioning stages – can check out undulator, characterize e beam, and boot-strap up to shorter wavelengths.


Spontaneous vs. FEL Radiation Spontaneous vs. FEL Radiation -3--3-



Workshop RecommendationsWorkshop Recommendations

No Intra-Undulator-Segment X-Ray Diagnostics in Baseline DesignInstead: End-of-Undulator X-Ray Diagnostics

CCD Camera (9 mm Pixel Resolution, 1024 x 1024 Area)Spectrometer

Trajectory Distortion Method to Characterize FEL Radiation vs. zInvestigation of Spontaneous Radiation as Diagnostics ToolsCode Development to Support CommissioningAreas for Follow-Up R&D

Study of Spectral and Spatial Distribution of Spontaneous RadiationDiagnostics PrototypingMicrobunching Measurement

No Intra-Undulator-Segment X-Ray Diagnostics in Baseline DesignInstead: End-of-Undulator X-Ray Diagnostics

CCD Camera (9 mm Pixel Resolution, 1024 x 1024 Area)Spectrometer

Trajectory Distortion Method to Characterize FEL Radiation vs. zInvestigation of Spontaneous Radiation as Diagnostics ToolsCode Development to Support CommissioningAreas for Follow-Up R&D

Study of Spectral and Spatial Distribution of Spontaneous RadiationDiagnostics PrototypingMicrobunching Measurement


Draft Commissioning Schedule


ConclusionsConclusions

Requirements for LCLS undulator are well established

LCLS undulator performance requirements are well understood

Risks have been assessed and undulator specifications address the risk

Commissioning plan is under development

Requirements for LCLS undulator are well established

LCLS undulator performance requirements are well understood

Risks have been assessed and undulator specifications address the risk

Commissioning plan is under development


End of Presentation

undulator physics april 29, 2004 heinz-dieter nuhn, slac / ssrl facility advisory committee meeting...

Documents

undulator parameter3

undulator period3

hall undulator slide

commissioning strategy

tm average function

gev30m average function

period length3

sase fel