Undulator Physics Diagnostics Commissioning Strategy HeinzDieter Nuhn, SLAC SSRL August 11, 2004

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Undulator PhysicsDiagnostics / Commissioning
StrategyHeinz-Dieter Nuhn, SLAC / SSRLAugust
11, 2004

• Undulator Overview
• FEL Parameters
• Diagnostics and Commissioning Strategy

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Linac Coherent Light Source
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Undulator Segment Prototype
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Workshops and Meetings

• Undulator Parameter Workshop
• October 24, 2003, Argonne
• URL http//www-ssrl.slac.stanford.edu/lcls/undula
  tor/meetings/2003-10-24_parameter_workshop/
• Undulator Review
• November 14, 2003, Argonne
• URL http//www-ssrl.slac.stanford.edu/lcls/undula
  tor/meetings/2003-11-14_review/
• Undulator Diagnostics and Commissioning Workshop
• January 19-20, 2004, UCLA
• URL http//www-ssrl.slac.stanford.edu/lcls/undula
  tor/meetings/2004-01-19_diagnostics_comissioning/
• Report http//www-ssrl.slac.stanford.edu/lcls/wor
  kshops/2004-09-22_diag_comm/lcls-tn-04-2.pdf
• Undulator Systems Review
• March 3-4, 2004, Argonne
• URL http//www-ssrl.slac.stanford.edu/lcls/undula
  tor/meetings/2004-03-03_review/
• Undulator Physics and Engineering Meeting
• June 28-29, 2004, Argonne
• URL http//www-ssrl.slac.stanford.edu/lcls/undula
  tor/meetings/2004-06-28_phy_eng/
• Undulator Meeting
• July 23, 2004, Argonne
• URL http//www-ssrl.slac.stanford.edu/lcls/undula
  tor/meetings/2004-07-23_und_mtg/

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Undulator Design Changes Since May 2003

• 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

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Amplitudes of Undulator 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 Specification Documents

• Controlled Specification Documents support
  Inter-Laboratory Communications
• Global Requirements Document (GRD)
• GRD 1.1-001 (http//www-ssrl.slac.stanford.edu/lcl
  s/prd/1.1-001-r1.pdf)
• Physics Requirements Documents (PRDs)
• PRD 1.4-001 General Undulator System Requirements
  (http//www-ssrl.slac.stanford.edu/lcls/prd/1.4-00
  1-r0.pdf)
• PRD 1.4-002 Magnetic Measurement Facility
  Requirements (http//www-ssrl.slac.stanford.edu/lc
  ls/prd/1.4-002-r0.pdf)
• PRD 1.4-003 Beam Based Alignments System
  Requirements (http//www-ssrl.slac.stanford.edu/lc
  ls/prd/1.4-003-r0.pdf)
• PRD 1.1-314 LCLS Beam Position Measurement System
  Requirements (http//www-ssrl.slac.stanford.edu/lc
  ls/prd/1.1-314-r0.pdf)
• Engineering Specification Documents (ESDs)
• ESD 1.4-100 Undulator Segment Specifications
• ESD 1.4-101 Undulator Segment Support
  Specifications
• ESD 1.4-102 Quadrupole Magnet Specifications
• ESD 1.4-103 Diagnostics System Specifications
• ESD 1.4-104 Wire Position Monitor System
  Specifications
• ESD 1.4-105 Hydrostatic Leveling System
  Specification
• ESD 1.4-106 Vacuum System Specifications
• ESD 1.4-106 Controls Specifications
• Interface Control Documents (ICDs)
• ICD 1.4-500 Undulator Mechanical Interfaces

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FEL 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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Workshop Issues

• 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

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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)
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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?
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FEL Gain Measurement

• Desirable measurements as function of position
  along undulator
• Intensity (LG, Saturation)
• Spectral Distribution
• Bunching

Saturation
Exponential Gain Regime
Undulator Regime
1 of X-Ray Pulse
Electron BunchMicro-Bunching
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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.
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End-of-Undulator Commissioning Diagnostics

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

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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
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Measurement 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 End-Of-Undulator Diagnostics
• Turn-Off Gain at Selectable Point Along Undulator
  by
• Introduction of orbit distortion
• Removal of undulator segments (New roll-away
  option)
• Characterize x-ray beam at single station down
  stream of undulator

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Measurement of SASE Gain withend-of-undulator
diagnostics

• GENESIS Simulations by Z. Huang

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Spontaneous vs. FEL Radiation -1-
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Spontaneous vs. FEL Radiation -2-
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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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Conclusions

• Requirements for LCLS undulator are well
  established
• LCLS undulator performance requirements are well
  understood
• Risks have been assessed and undulator
  specifications address the risk
• Detailed commissioning strategy is being
  developed. 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