Introduction Heinz-Dieter Nuhn, SLAC / LCLS November 14, 2005

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IntroductionHeinz-Dieter Nuhn, SLAC /
LCLSNovember 14, 2005

• Need for Beam Based Undulator K Measurements
• Review of Beam Based K Measurement Discussions
• LCLS Undulator Diagnostics Baseline Components
• LCLS FEL Commissioning Milestones
• Workshop Objective and Agenda
• Charge to the Workshop

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Linac Coherent Light Source
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Summary of Nominal Undulator Parameters

• Undulator Type planar hybrid
• Magnet Material NdFeB
• Wiggle Plane horizontal
• Gap 6.8 mm
• Period Length 30.0 0.05 mm
• Effective On-Axis Field 1.249 T
• Standard Effective K 3.500 0.015
• Range of Effective Undulator Parameter K 3.500 -
  3.493 (3.480)
• Accumulated Segment Phase Error Tolerance
  10 degrees(at any point along segment)
• Module Length 3.40 m
• Number of Modules 33
• Undulator Magnet Length 112.2 m
• Standard Break Lengths 48.2 - 48.2 - 94.9 cm
• Nominal Total Device Length 130.954 m
• Quadrupole Magnet Technology EMQ
• Nominal Quadrupole Magnet Length 7 cm

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Undulator Segment Prototype
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Undulator Pole Canting

• Canting comes from wedged spacers
• 4.5 mrad cant angle
• 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

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Using Undulator Roll-Away and K Adjustment
Function

• Horizontal position of undulator segment can be
  remotely controlled correct Keff on beam axis
• This adjustment range goes from fraction of a
  percent to a complete field turn-off.

Neutral K3.5000 Dx0.0 mm
PowerTp K3.4804 Dx8.5 mm
Beam Axis
SpontTp K3.4929 Dx3.0 mm
RollAway K0.0000 Dx100 mm
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Measurement of Spontaneous Radiation Using Rollout
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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Insufficient Knowledge of Actual K Seen by
Electrons

• Effects Influencing Keff
• Undulator Segment Tuning
• Undulator Temperature
• Transverse Segment Position
• Segment Fiducialization and Alignment
• Electron Beam Trajectory
• Environmental Field in Undulator Hall
• Radiation Damage

See Tolerance Budget on next Slide
Need for Beam Based Undulator K Measurements
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Segment Detuning Sub-Budget
Parameter pi Typical Value rms dev. dpi Note
KMMF 3.5 0.0003 0.015 uniform
aK -0.0019 C-1 0.0001 C-1 Thermal Coefficient
DT 0 C 0.32 C 0.56 C uniform without compensation
bK 0.0023 mm-1 0.00004 mm-1 Canting Coefficient
Dx 1.5 mm 0.05 mm Horizontal Positioning
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Discussions of Beam Based K Measurements Based on
Spontaneous Undulator Radiation

• January 2004 Z. Huang
• Sven Reiche
• September 2004 LCLS Diagnostics and
  Commissioning Workshop
• High-Resolution Effective K Measurements Using
  Spontaneous Undulator Radiation, Bingxin Yang
  http//www-ssrl.slac.stanford.edu/lcls/workshops/
  2004-09-22_diag_comm/bxyang_CommWorkshop200409.ppt
  
• October 2004 LCLS Week
• Undulator / FEL Diagnostics, Bingxin Yang
  https//www-ssrl.slac.stanford.edu/lcls/fac/talks
  _oct2004/Yang_FAC200410.ppt
• January 2005 LCLS FEL Physics Meeting
• Simulation Results for 200-pC ("chargito") SASE
  performance with AC Wake, Jim Welch
  http//www-ssrl.slac.stanford.edu/lcls/internals/
  felphysics/2005-01-18/k_meas_talk.ppt
• April 2005 ICFA Commissioning Workshop at Zeuthen
  (Work Package 6)
• Measurement of Undulator Segment K_effective
  using Spontaneous Radiation in the Near Hall of
  the LCLS, Jim Welch http//adweb.desy.de/mpy/ICFA2
  005_Commissioning/Talks(PDF)/April202120(Thursda
  y)/WP6_1/Welch_Undulator20Commissioning.pdf
• High resolution undulator measurements using
  angle-integrated spontaneous spectra, Bingxin
  Yang http//adweb.desy.de/mpy/ICFA2005_Commission
  ing/Talks(PDF)/April202120(Thursday)/WP6_2/Yang_
  High20Resolution20Undulator20measurements.pdf
• July 2005 LCLS Week
• K-Measurement Strategies discussion presented by
  Jim Welch and Bingxin Yang
• October 2005 FAC Meeting
• X-Ray Diagnostic, Richard Bionta
  http//ssrl.slac.stanford.edu/lcls/fac/talks_oct_
  2005/bionta_xtod_diagnostics_fac.ppt

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Review of Existing LCLS Baseline Diagnostics

• Diagnostics presently being developed to
  Characterize Electron Beam and X-Ray Properties
  include
• Electron Beam Diagnostics in the
  Linac-To-Undulator (LTU) Beamline
• Electron Beam and X-Ray Diagnostics in the
  Undulator
• Electron Beam Diagnostics after the Undulator
  (Dump Line)
• X-Ray Diagnostics in the Front End Enclosure (FEE)

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LTU Electron Beam Diagnostics

• Control of Electron Beam Properties before
  Entrance into the Undulator

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LTU
abort dump
1 OTR ? slice-(e, b, g)
OTR ? slice E-spread (0.02)
4 wires ? e, b, g ( collimators)
2 BPMs ? energy jitter
x1
x2
relative energy centroid resolution 0.003 (5-mm
BPMs)
Courtesy of Paul Emma
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X-Ray Beam Diagnostics

• Control of Electron Beam Trajectory inside the
  Undulator

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Short Break Section Components
Beam Finder Wire
RF Cavity BPM
Quadrupole
Undulator Segment
Cherenkov Detector
Undulator Segment
Courtesy of Dean Walters
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Long Break Section Components
Beam Finder Wire
Diagnostics Tank
RF Cavity BPM
Quadrupole
Undulator Segment
Cherenkov Detector
Undulator Segment
Courtesy of Dean Walters
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After Undulator Electron Beam Diagnostics

• Electron Beam Diagnostics after Undulator

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Dump-Line
1 OTR ? energy-spread (0.001)
1 BPM ? energy-jitter (0.003)
Courtesy of Paul Emma
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Diagnostics in the Front End Enclosure

• Measurement of X-Ray Beam Properties in FEE

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FEE Layout
Slit
Be Mirrors 2 3
Diagnostics Package
Solid Attenuator
Collimator 1
Fast close valve
Gas Attenuator
Ion Chamber
SiC Mirror 1
Ion Chamber
Diagnostics Package
SiC Mirror 2
Courtesy of Richard Bionta
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Desired Spontaneous Measurements
f(x,y,l1) Spatial distribution around l1
l1 1st harmonic Photon wavelength
Dl/l1 1st harmonic wavelength spread
Beam direction
u Total energy / pulse
su,sl1 Temporal variation in beam parameters
Courtesy of Richard Bionta
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FEE Cartoon
Start of Experimental Hutches
5 mm diameter collimators
Windowless Ion Chamber
Diagnostic Package
Spectrometer / Indirect Imager mirror
Solid Attenuator
High-Energy Slit
Total Energy Calorimeter
e-
WFOV Direct Imager
Gas Attenuator
FEL Offset mirror system
Spectrometer camera
Windowless Ion Chamber
Muon Shield
Courtesy of Richard Bionta
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Redundant Commissioning Instrumentation
Instrument Purpose Adjustment Calibration and Physics risks
Direct Imager SP f(x,y), look for FEL, measure FEL u, f(x,y), x,y ND filter, Attenuators Scintillator linearity, Attenuator linearity and background
Indirect Imager Measure FEL u, f(x,y), spectral imaging of SP and FEL harmonics, attenuator calibration Mirror Angle Mirror reflectivity, damage
Total Energy FEL u Attenuators Energy to Heat, damage
Ion Chamber FEL u, x,y,x',y' Pressure Signal strength
Spectrometers FEL, SP spectra Attenuators Resolution, damage
Courtesy of Richard Bionta
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LCLS FEL Commissioning Milestones

• MS3BO_040 Front End Beneficial Occupancy
  (9/5/2007)
• MS3BO_030 Undulator Facility Beneficial
  Occupancy (12/3/2007)
• MS3_XT040 Solid Attenuator Installation Complete
  (12/14/2007)
• MS3_XT045 Gas Attenuator Installation Complete
  (12/14/2007)
• MS3_XT080 Start Front End Enclosure
  Commissioning (3/4/2008)
• MS3_LN015 Start Linac-to-Undulator (LTU)
  Commissioning (5/12/2008)
• MS3_XT066 Start Near Experimental Hall Checkout
  (6/12/2008)
• MS3_UN020 Undulator System Installation Complete
  (7/18/2008)
• MS3_UN025 Start Undulator Commissioning (1st
  Light) (7/24/2008)

Diagnostics needed around July 2008
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Workshop Objective

• Define a strategy for using spontaneous undulator
  radiation to measure the K value of every
  individual LCLS Undulator Segment after
  installation in the Undulator Hall.
• To reach the objective, the physics and
  technologies necessary need to be identified.
  Workshop discussions will include
• Usable spectral features of spontaneous radiation
  
• Strategies for beam-based K measurements
• Specifications for suitable instruments
• Scheduling issues
• Three Work Packages have been defined and
  assigned to three different groups. Work
  described by these Work Packages has been carried
  out in preparation of the workshop and will be
  presented and discussed at the workshop.

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Workshop Agenda
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Work Package 1 Angle Integrated Measurement

• Group B. Yang, R. Dejus
• Task Examine robustness of angle-integrated
  measurements of undulator spectrum. Consider
  effects of errors in beam alignment, undulator
  magnet structure, straightness of vacuum pipe,
  alignment of spectrometer, etc. Consider effects
  of location of undulator segment being tested.
  Determine what are realistic values for the
  precision with which the value of K can be
  determined for an undulator segment at the
  beginning, middle, and end of the undulator.
  This task explores the use of the high-energy
  edge of the fundamental spectral peak (the third
  harmonic may also be considered) of a single
  undulator to measure its K parameter. The
  measuring spectrometer will be located in the
  LCLS FEE, roughly 100 m downstream from the final
  undulator segment. Realistic values for the
  angular acceptance of the measurement (limited by
  beam-pipe apertures, or apertures at the
  measuring point) should be considered.

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Work Package 2 Pinhole Measurement

• Group J. Welch, R. Bionta, S. Reiche
• Task Examine robustness of pinhole measurements
  of undulator spectrum. Consider effects of errors
  in beam alignment, undulator magnet structure,
  straightness of vacuum pipe, alignment of pinhole
  and spectrometer, etc. Consider effects of
  location of undulator segment being tested.
  Determine what are realistic values for the
  precision with which the value of K can be
  determined for an undulator segment at the
  beginning, middle, and end of the undulator.
  This task explores the use of the fundamental
  spectral peak (the third harmonic may also be
  considered) of a single undulator, as seen
  through a small angular aperture, to measure its
  K parameter. The measuring spectrometer will be
  located in the LCLS FEE, roughly 100 m downstream
  from the final undulator segment. Realistic
  values for the angular acceptance of the
  measurement should be determined, and the effects
  of misalignment of the aperture or undulator axis
  should be carefully considered.

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Work Package 3 Single-Shot Spectral Measurement

• Group J. Hastings, et al.
• Task Assume that a single shot spectral
  measurement is needed for an LCLS spontaneous
  undulator pulse. What are the best options for
  doing the measurement? What spectral resolution
  can be obtained using these methods? What are the
  effects of beam jitter, spectrometer
  misalignment, etc? This task explores the
  design and performance of x-ray spectrometers
  capable of providing centroid or edge position
  with high resolution, on a single-shot of
  radiation from a single LCLS undulator. The
  spectrometer will most likely be located in the
  LCLS FEE, about 100 m downstream from the final
  undulator segment.

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Workshop Charge

• Characterize the spectral features of spontaneous
  synchrotron radiation that are usable for
  beam-based K-measurements.
• Identify the most appropriate strategy for
  beam-based K-measurements.
• Specify suitable instruments for the identified
  beam-based K-measurement strategy.
• List expected performance parameters such as
  resolution of K measurement as function of beam
  charge, and segment location as well as expected
  tolerances to trajectory and energy jitter.
• List any open questions regarding the feasibility
  of the most appropriate strategy.
• List the RD activities, if any, needed before
  the design of a measurement system can be
  completed and manufacturing/procurement can start.

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End of Presentation