Undulator / FEL Commissioning Plans Heinz-Dieter Nuhn, SLAC / SSRL September 22, 2004

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Undulator / FEL Commissioning PlansHeinz-Dieter
Nuhn, SLAC / SSRLSeptember 22, 2004

• FY2004 Undulator Parameter Changes
• Summary of January Undulator Commissioning
  Workshop
• Undulator Commissioning Issues
• FEL Characterization

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Linac Coherent Light Source
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(No Transcript)
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FEL Design Changes Since the May 2003 Lehman
Review

• Canting of Undulator Poles
• Remote Undulator Roll-Away and K Adjustment
  Function
• Increase in Undulator Gap
• Reduction in Maximum Beam Energy
• Reduction in Quadrupole Gradient
• Increase in Beta Function
• Increase in Break Section Length
• ? Electromagnetic Quadruples

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New Undulator Pole Canting
Suggested by J. Pflueger, DESY

• Canting comes from wedged spacers
• 4.5 mrad cant
• Gap can be adjusted by lateral displacement of
  wedges
• 1 mm shift means 4.5 microns in gap, or 8.2 Gauss
  
• Beff adjusted to desired value

Courtesy of Liz Moog
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Undulator Roll-Away and K Adjustment Function
Neutral K3.4965 Dx0.0 mm
First K3.5000 Dx-1.5 mm
PowerTp K3.4804 Dx7.0 mm
Last K3.4929 Dx1.5 mm
RollAway K0.0000 Dx100 mm
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Effective B field vs. x

• Measured slope of 6.6 Gauss/mm agrees with
  calculations( 5.7 Gauss/mm for 3 mrad cant)
• Field variation allowance between segments is
  DB/B 1.5x10-4, or DB 2 Gauss, which
  translates to Dx 0.3 mm ( or 1 micron in gap)

Courtesy of Liz Moog
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Canting the poles helps in many ways

• Facilitates final setting of Beff
• Remote control of position allows run-time
  adjustment
• Allows compensating for temperature effect on
  field strength 1.0C temperature error would
  require 1.2 mm lateral shift of undulator

Courtesy of Liz Moog
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RMS phase error at different x positions

• No significant dependence on X
• An RMS phase error of 6.5 degree is an upper
  limit for near-perfect (100) performance

Courtesy of Liz Moog
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Period-averaged horizontal trajectories at 14.1
GeV
(X in mm)

• Trajectories are all well behaved and well within
  the 2 mm tolerance for maximum walk-off from a
  straight line

Courtesy of Liz Moog
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Amplitudes of FEL Parameter Changes

• May 2003 August 2004
• Undulator Type planar hybrid
• Magnet Material NdFeB
• Wiggle Plane horizontal
• Gap 6.0 6.8 mm
• Gap Canting Angle 0.0 4.5 mrad
• Period Length 30.0 0.1 mm
• Effective On-Axis Field 1.325 1.249 T
• Effective Undulator Parameter K 3.630 0.015
  3.500 0.015
• Module Length 3.40 m
• Number of Modules 33
• Undulator Magnet Length 112.2 m
• Standard Break Lengths 18.7 - 18.7 - 42.1 48.2 -
  48.2 - 94.9 cm
• Total Device Length 121.0 131.9 m
• Lattice Type FODO

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Performance Impact of Changes (1.5 Å)

• May 2003 August 2004 Change
• Electron Beam Energy 14.35 13.64 GeV -5.0
• Emittance 0.043 0.045 nm rad 5.2
• Avg. Electron Beam Radius 27 35 µm 27.5
• Avg. Electron Beam Divergence 1.6 1.3 µrad -17.5
  
• Peak Beam Power 49 46 TW -5.0
• FEL Parameter (3D) 0.00033 0.00032 -3.5
• Power Gain Length (3D) 4.2 4.3 m 3.6
• Saturation Length (w/o Breaks) 82 86 m 4.9
• Saturation Length (w/ Breaks) 89 101 m 13.5
• Peak Saturation Power 7.4 7.6 GW 2.5
• Coherent Photons per Pulse 1.41012 1.51012 2.5
  
• Peak Brightness 1.51033 1.51033 2.5
• Average Brightness 4.61022 4.71022 2.5
• Peak Spont. Power per Pulse 91 73 GW -19.7
• Increase due to 3D effects (reduction in
  diffraction due to beam radius increase)
• Ph./s/mm2/mr2/.1

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Undulator / FEL Commissioning Documents

• Report of the LCLS Diagnostics and Commissioning
  WorkshopSLAC-R-715, LCLS-TN-04-02http//www-ssr
  l.slac.stanford.edu/lcls/technotes/LCLS-TN-04-2.pd
  f
• LCLS PRD1.1-002 LCLS Start-Up Test
  Planhttp//www-ssrl.slac.stanford.edu/lcls/prd/1
  .1-002-r0.pdf

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Undulator Diagnostics and Commissioning Workshop
1/19-20/04

• Scope
• Commissioning of the FEL Undulator with Beam
• Goals
• 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
• 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 ChargeSingle Shot
Low Charge, 10 Hz
10 Hz
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January 2004 Workshop Recommendations

• No Intra-Undulator-Segment X-Ray Diagnostics in
  Baseline Design
• Instead End-of-Undulator X-Ray Diagnostics to
  Characterize FEL Radiation vs. z
• Trajectory Distortion Method
• Roll-Away Undulator Segments Function
• Investigation of Spontaneous Radiation as
  Diagnostics Tools
• Code Development to Support Commissioning
• Areas for Follow-Up RD
• Study of Spectral and Spatial Distribution of
  Spontaneous Radiation
• Diagnostics Prototyping
• Microbunching Measurement

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Commissioning Phases

• Phase 0 Beam Through Undulator (at 0.2 nC, sngl
  shot)
• Phase I Spontaneous Radiation (at 0.2 nC, 10
  Hz)
• Parameters Energy 4.31-13.64 GeV, Emittance not
  critical
• Goals Establish straight and stable trajectory,
  measure spontaneous radiation
• Phase II a Low Energy FEL Radiation (at 0.2-1
  nC, 10 Hz)
• Parameters Energy 4.31 GeV, Emittance lt 4
  microns Peak Current lt 1 kA
• Goals Characterize FEL radiation. Achieve
  saturation.
• Phase II b High Energy FEL Radiation (at 0.2-1
  nC, 10 Hz)
• Parameters Energy gt4.31 -13.64 GeV, Emittance
  1.2- 4 microns Peak Current 1-3.4 kA
• Goals Characterize FEL radiation, gain. Achieve
  saturation.
• Phase III Transition to Operation (at 0.2-1 nC,
  120 Hz)
• Parameters Energy gt4.45 -13.64 GeV, Emittance
  1.2- 4 microns Peak Current 1-3.4 kA
• Goals Bring FEL performance up to full operating
  performance levels.

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LTU / Undulator Commissioning Issues

• Undulator Radiation Protection
• Collimators
• Tune-Up Dump
• Roll-Away Undulators
• Radiation Interlocks
• 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

See next talk by Sven Reiche !
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Undulator Radiation Protection
Two-Phase, Two-Plane Collimation, 1½ Times
p/2
p/2
?3 mm
?2.5 mm
edge scattering
?2 mm
halo
e- beam
undulator beam pipe
x1
x2
x3
phase-1 again
phase-2
phase-1
(also collimation in y and energy see next
slides)
Courtesy of Paul Emma
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LCLS Collimation Proposal (2 energy, 3 x, and 3 y
adjustable collimators)
y1
y2
y3
x3 y3 optional?
muon shielding
E1
E2
x1
x2
x3
undulator
Courtesy of Paul Emma
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2-phase, 2-plane, and energy collimation in
2nd-order
Dy mm
Dx mm
Coll.
2nd-order tracking with all collimators closed
and big halo
-
?5.0
CE1
-
?5.0
CE2
-
?2.0
CX1
?2.0
-
CY1
?2.5 mm
-
?2.0
CX2
?2.0
-
CY2
-
?
CX3
?
-
CY3
well shadowed in x, y, and E
gex,y 4000 mm, sE/E 10 (uniform)
Courtesy of Paul Emma
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• Track 100 times with
• DL2 BPM rms res. 10 mm
• DL2 BPM rms misa. 200 mm
• DL2 Quad rms misa. 200 mm
• Undulator Quad rms misa. 100 mm
• Correct und-launch, then open stopper-2 for one
  beam shot
• Just 11 of 100 trajectories exceed ?2.5 mm within
  undulator
• None exceed ?3.5 mm

G 110 T/m
First beam shot through undulator?
Courtesy of Paul Emma
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FEL Gain Measurement

• Desirable measurements as function of position
  along undulator
• Intensity (LG, Saturation)
• Spectral Distribution
• Bunching
• Total energy
• Pulse length
• Photon energy spectra
• Spatial coherence
• Spatial shape and centroid
• Divergence

Saturation
Exponential Gain Regime
Undulator Regime
1 of X-Ray Pulse
Electron BunchMicro-Bunching
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Quantities to be Measured

• Total energy
• Pulse length
• Photon energy spectra
• Spatial coherence
• Spatial shape and centroid
• Divergence

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Dose / Power Considerations
Fluence to Melt
Energy Density Reduction of a Reflector
Be will melt at normal incidence at E lt 3 KeV
near undulator exit. Using Be as a grazing
incidence reflector may gain x 10 in tolerance.
Courtesy of Richard Bionta
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Measurement of SASE Gain along the undulator

• Direct Detectors in the Breaks between Undulator
  Segments.
• Fluence levels too large for x-ray!.
• Alternative End-Of-Undulator Diagnostics
• Turn-Off Gain at Selectable Point Along Undulator
  by
• Introduction of trajectory distortion
• Removal of undulator segments (New roll-away
  option)
• Characterize x-ray beam at single station down
  stream of undulator

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4' Muon shield
PPS
Access Shaft
PPS
Spectrometer, Total Energy
Solid Attenuator
Access Shaft
Direct Imager Indirect Imager
Slit A
Slit B
Windowless Ion Chamber
PPS
Gas Attenuator
13' Muon shield
Fast close valve
Courtesy of Richard Bionta
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Measurement of SASE Gain withTrajectory
Distortion
Quadrupole Displacement at Selectable Point along
Undulator

• GENESIS Simulations by Z. Huang

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Measurement of SASE Gain Using Rollaway Option
Undulator Segments can be removed by remote
control from the end of the undulator. They will
not effect radiation produced by earlier segments.
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Spontaneous vs. FEL Radiation -1-
See Thursday talk by Paul Emma Weak FEL Signal
Detection Using a Slowly Modulated Laser-Heater
Figure by S. Reiche
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Spontaneous vs. FEL Radiation -2-
Figure by S. Reiche
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Conclusions

• Several Undulator Parameters have been Changed.
• New K Adjustment and Roll-Away Option will aid
  undulator and FEL commissioning.
• FEL and Spontaneous Radiation Diagnostics will be
  located after the end of the undulator
• Detailed commissioning strategy is being
  developed. First Startup Test Plan exists.
• PRD 1.1-002 LCLS Start-Up Test Plan
  (http//www-ssrl.slac.stanford.edu/lcls/prd/1.4100
  2-r1.pdf)

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End of Presentation