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

1. 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

2. Far Hall Undulator Near Hall Linac Coherent Light Source

4. 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

5. 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

6. Undulator Roll-Away and K Adjustment Function Neutral; K=3.4965; Dx=+0.0 mm First; K=3.5000; Dx=-1.5 mm PowerTp; K=3.4804; Dx=+7.0 mm Last; K=3.4929; Dx=+1.5 mm RollAway; K=0.0000; Dx=+100 mm

7. 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

8. 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: ±1.0°C temperature error would require ±1.2 mm lateral shift of undulator Courtesy of Liz Moog

9. 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

10. 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

11. Amplitudes of FEL Parameter Changes May 2003August 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 - 42.148.2 - 48.2 - 94.9 cm Total Device Length 121.0131.9 m Lattice Type FODO Integrated QF Gradient 5.355 3.000 T/m Integrated QD Gradient -5.295-3.000 T/m Average b Function at 1.5 Å 18 30 m Average b Function at 15. Å 7.3 8.9 m

12. Performance Impact of Changes (1.5 Å) May 2003August 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 1.4×1012 1.5×1012 +2.5 %* Peak Brightness 1.5×1033 1.5×1033 ** +2.5 %* Average Brightness 4.6×1022 4.7×1022 ** +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%]

13. Undulator / FEL Commissioning Documents • “Report of the LCLS Diagnostics and Commissioning Workshop”SLAC-R-715, LCLS-TN-04-02http://www-ssrl.slac.stanford.edu/lcls/technotes/LCLS-TN-04-2.pdf • LCLS PRD1.1-002 “LCLS Start-Up Test Plan”http://www-ssrl.slac.stanford.edu/lcls/prd/1.1-002-r0.pdf

14. 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

15. 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 R&D • Study of Spectral and Spatial Distribution of Spontaneous Radiation • Diagnostics Prototyping • Microbunching Measurement

16. 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: < 4 microns Peak Current : < 1 kA • Goals: Characterize FEL radiation. Achieve saturation. • Phase II b: High Energy FEL Radiation (at 0.2-1 nC, 10 Hz) • Parameters: Energy: >4.31 -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: >4.45 -13.64 GeV, Emittance: 1.2- 4 microns Peak Current : 1-3.4 kA • Goals: Bring FEL performance up to full operating performance levels.

17. 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 !

18. 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

19. 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

20. 2-phase, 2-plane, and energy collimation in 2nd-order Coll. Dx mm Dy mm 2nd-order tracking with all collimators closed and big halo CE1 5.0 - CE2 5.0 - CX1 2.0 - CY1 - 2.0 2.5 mm CX2 2.0 - CY2 - 2.0 CX3 ? - CY3 - ? well shadowed in x, y, and E gex,y = 4000 mm, sE/E = 10% (uniform) Courtesy of Paul Emma

21. 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

22. 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

23. Quantities to be Measured • Total energy • Pulse length • Photon energy spectra • Spatial coherence • Spatial shape and centroid • Divergence

24. Dose / Power Considerations 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 Richard Bionta

25. 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

26. 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

27. Measurement of SASE Gain withTrajectory Distortion GENESIS Simulations by Z. Huang Quadrupole Displacement at Selectable Point along Undulator

28. 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.

29. 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

30. Spontaneous vs. FEL Radiation -2- Figure by S. Reiche

31. 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/1.41002-r1.pdf)

32. End of Presentation