1. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 1 Introduction Heinz-Dieter Nuhn, SLAC / LCLS November 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 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

2. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 2 Linac Coherent Light Source Near Hall Far Hall Undulator

3. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 3

4. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 4 Undulator Type planar hybrid Magnet Material NdFeB Wiggle Planehorizontal Gap6.8mm Period Length30.0 ± 0.05mm Effective On-Axis Field1.249T Standard Effective K3.500 ± 0.015% Range of Effective Undulator Parameter K3.500 - 3.493 (3.480) Accumulated Segment Phase Error Tolerance 10degrees (at any point along segment) Module Length3.40m Number of Modules33 Undulator Magnet Length112.2m Standard Break Lengths 48.2 - 48.2 - 94.9 cm Nominal Total Device Length130.954m Quadrupole Magnet Technology EMQ Nominal Quadrupole Magnet Length 7cm Integrated Quadrupole Gradient 3.0T Undulator Type planar hybrid Magnet Material NdFeB Wiggle Planehorizontal Gap6.8mm Period Length30.0 ± 0.05mm Effective On-Axis Field1.249T Standard Effective K3.500 ± 0.015% Range of Effective Undulator Parameter K3.500 - 3.493 (3.480) Accumulated Segment Phase Error Tolerance 10degrees (at any point along segment) Module Length3.40m Number of Modules33 Undulator Magnet Length112.2m Standard Break Lengths 48.2 - 48.2 - 94.9 cm Nominal Total Device Length130.954m Quadrupole Magnet Technology EMQ Nominal Quadrupole Magnet Length 7cm Integrated Quadrupole Gradient 3.0T Summary of Nominal Undulator Parameters

5. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 5 Undulator Segment Prototype

6. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 6 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 B eff adjusted to desired value

7. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 7 Using Undulator Roll-Away and K Adjustment Function Neutral; K=3.5000;  x=+0.0 mm SpontTp; K=3.4929;  x=+3.0 mmRollAway; K=0.0000;  x=+100 mm PowerTp; K=3.4804;  x=+8.5 mm Horizontal position of undulator segment can be remotely controlled correct K eff on beam axis This adjustment range goes from fraction of a percent to a complete field turn-off. Horizontal position of undulator segment can be remotely controlled correct K eff on beam axis This adjustment range goes from fraction of a percent to a complete field turn-off. Beam Axis

8. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 8 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.

9. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 9 Effects Influencing K eff Undulator Segment Tuning Undulator Temperature Transverse Segment Position Segment Fiducialization and Alignment Electron Beam Trajectory Environmental Field in Undulator Hall Radiation Damage Effects Influencing K eff Undulator Segment Tuning Undulator Temperature Transverse Segment Position Segment Fiducialization and Alignment Electron Beam Trajectory Environmental Field in Undulator Hall Radiation Damage Insufficient Knowledge of Actual K Seen by Electrons Need for Beam Based Undulator K Measurements See Tolerance Budget on next Slide

10. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 10 Segment Detuning Sub-Budget Parameter p i Typical Value rms dev.  p i Note K MMF 3.50.0003±0.015 % uniform KK -0.0019 °C -1 0.0001 °C -1 Thermal Coefficient TT 0 °C0.32 °C±0.56 °C uniform without compensation KK 0.0023 mm -1 0.00004 mm -1 Canting Coefficient xx 1.5 mm0.05 mmHorizontal Positioning

11. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 11 January 2004 Z. Huang Sven Reiche September 2004: LCLS Diagnostics and Commissioning Workshop High-Resolution Effective K Measurements Using Spontaneous Undulator RadiationHigh-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 DiagnosticsUndulator / 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 WakeSimulation 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 LCLSMeasurement of Undulator Segment K_effective using Spontaneous Radiation in the Near Hall of the LCLS, Jim Welch http://adweb.desy.de/mpy/ICFA2005_Commissioning/Talks(PDF)/April%2021%20(Thursday)/WP6_1/Welch_Undulator%20Commissioning.pdf High resolution undulator measurements using angle-integrated spontaneous spectra, High resolution undulator measurements using angle-integrated spontaneous spectra, Bingxin Yang http://adweb.desy.de/mpy/ICFA2005_Commissioning/Talks(PDF)/April%2021%20(Thursday)/WP6_2/Yang_High%20Resolution%20Undulator%2 0measurements.pdf July 2005 LCLS Week: K-Measurement Strategies discussion presented by Jim Welch and Bingxin Yang October 2005 FAC Meeting X-Ray DiagnosticX-Ray Diagnostic, Richard Bionta http://ssrl.slac.stanford.edu/lcls/fac/talks_oct_2005/bionta_xtod_diagnostics_fac.ppt January 2004 Z. Huang Sven Reiche September 2004: LCLS Diagnostics and Commissioning Workshop High-Resolution Effective K Measurements Using Spontaneous Undulator RadiationHigh-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 DiagnosticsUndulator / 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 WakeSimulation 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 LCLSMeasurement of Undulator Segment K_effective using Spontaneous Radiation in the Near Hall of the LCLS, Jim Welch http://adweb.desy.de/mpy/ICFA2005_Commissioning/Talks(PDF)/April%2021%20(Thursday)/WP6_1/Welch_Undulator%20Commissioning.pdf High resolution undulator measurements using angle-integrated spontaneous spectra, High resolution undulator measurements using angle-integrated spontaneous spectra, Bingxin Yang http://adweb.desy.de/mpy/ICFA2005_Commissioning/Talks(PDF)/April%2021%20(Thursday)/WP6_2/Yang_High%20Resolution%20Undulator%2 0measurements.pdf July 2005 LCLS Week: K-Measurement Strategies discussion presented by Jim Welch and Bingxin Yang October 2005 FAC Meeting X-Ray DiagnosticX-Ray Diagnostic, Richard Bionta http://ssrl.slac.stanford.edu/lcls/fac/talks_oct_2005/bionta_xtod_diagnostics_fac.ppt Discussions of Beam Based K Measurements Based on Spontaneous Undulator Radiation

12. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 12 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) 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) Review of Existing LCLS Baseline Diagnostics

13. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 13 Control of Electron Beam Properties before Entrance into the Undulator LTU Electron Beam Diagnostics

14. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 14 4 wires  , ,  (+ collimators) 1 OTR  slice- , ,  abort dump OTR  slice E-spread (0.02%) x1x1x1x1 x2x2x2x2 2 BPMs  energy jitter relative energy centroid resolution: 0.003% (5-  m BPMs) LTU Courtesy of Paul Emma

15. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 15 Control of Electron Beam Trajectory inside the Undulator X-Ray Beam Diagnostics

16. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 16 Short Break Section Components Courtesy of Dean Walters Quadrupole Undulator Segment Cherenkov Detector Undulator Segment RF Cavity BPM Beam Finder Wire

17. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 17 Long Break Section Components Quadrupole Undulator Segment Cherenkov Detector Undulator Segment Diagnostics Tank Beam Finder Wire RF Cavity BPM Courtesy of Dean Walters

18. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 18 Electron Beam Diagnostics after Undulator After Undulator Electron Beam Diagnostics

19. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 19 1 OTR  energy-spread (0.001%) 1 BPM  energy-jitter (0.003%) Dump-Line Courtesy of Paul Emma

20. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 20 Measurement of X-Ray Beam Properties in FEE Diagnostics in the Front End Enclosure

21. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 21 FEE Layout Fast close valve Slit Ion Chamber Diagnostics Package Gas Attenuator Solid Attenuator SiC Mirror 1 Be Mirrors 2 & 3 SiC Mirror 2 Collimator 1 Diagnostics Package Courtesy of Richard Bionta

22. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 22 Desired Spontaneous Measurements f(x,y, 1 )Spatial distribution around 1 1 1st harmonic Photon wavelength   1st harmonic wavelength spread Beam direction uTotal energy / pulse  u,  1 Temporal variation in beam parameters Courtesy of Richard Bionta

23. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 23 FEE Cartoon Solid Attenuator Gas Attenuator High-Energy Slit Start of Experimental Hutches 5 mm diameter collimators Muon Shield FEL Offset mirror system Total Energy Calorimeter WFOV Direct Imager Spectrometer / Indirect Imager mirror Windowless Ion Chamber e-e- Diagnostic Package Spectrometer camera Courtesy of Richard Bionta

24. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 24 Redundant Commissioning Instrumentation InstrumentPurposeAdjustmentCalibration and Physics risks Direct ImagerSP f(x,y), look for FEL, measure FEL u, f(x,y), x,y ND filter, Attenuators Scintillator linearity, Attenuator linearity and background Indirect ImagerMeasure FEL u, f(x,y), spectral imaging of SP and FEL harmonics, attenuator calibration Mirror AngleMirror reflectivity, damage Total EnergyFEL uAttenuatorsEnergy to Heat, damage Ion ChamberFEL u, x,y,x',y'PressureSignal strength SpectrometersFEL, SP spectraAttenuatorsResolution, damage Courtesy of Richard Bionta

25. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 25 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 (1 st Light) (7/24/2008) 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 (1 st Light) (7/24/2008) LCLS FEL Commissioning Milestones Diagnostics needed around July 2008

26. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 26 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. 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. Workshop Objective

27. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 27 Workshop Agenda

28. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 28 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. 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. Work Package 1: Angle Integrated Measurement

29. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 29 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. 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. Work Package 2: Pinhole Measurement

30. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 30 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. 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. Work Package 3: Single-Shot Spectral Measurement

31. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 31 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 R&D activities, if any, needed before the design of a measurement system can be completed and manufacturing/procurement can start. 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 R&D activities, if any, needed before the design of a measurement system can be completed and manufacturing/procurement can start. Workshop Charge

32. Introduction – November 14, 2005 Heinz-Dieter Nuhn, SLAC / LCLS Beam Based Undulator Measurements Workshop Nuhn@slac.stanford.edu 32 End of Presentation