Undulator Physics Issues Heinz-Dieter Nuhn, SLAC / LCLS October 30, 2007

1. Undulator Physics IssuesHeinz-Dieter Nuhn, SLAC / LCLSOctober 30, 2007 • Vacuum Chamber Update • Tuning Status • First Article Quadrupole Measurements • Beam Loss Monitors 1

2. Vacuum Chamber Update • At the last FAC meeting the stainless steel chamber had been cut to produce samples for permeability and roughness measurements of the coated surface. • The measurements were completed after the meeting with negative results: • The surface roughness of the finished chamber was much larger (2.5 times the tolerance) than that of the untreated stainless steel samples. • The presence of the chamber significantly changed the on-axis magnetic field of the undulator.A particularly large modification of the effect of the phase shims was observed.[See presentation by Z. Wolf] • The effects on the magnetic field clearly made the stainless steel chamber unusable. • At the DOE review it was decided to slightly reduce roughness requirements and to examine three alternatives: • Extruded Aluminum [Argonne] • Aluminum Clam Shell [SLAC] • Plain Copper Pipe [Argonne] FALL-BACK SOLUTION • In the meantime, the Extruded Aluminum chamber development proceeded to produce a full vacuum chamber meeting all tolerances. 2

3. Tuning Results The procedures for tuning and measuring the LCLS undulator magnets are described in LCLS-TN-06-17 “LCLS Undulator Test Plan” The document identifies three distinct phases: • Rough Tuning • Fine Tuning • Tuning Results (Final Measurements) During Rough Tuning, a target position (Slot number) is assigned to the undulator based on its strength and the gap height is adjusted according to the Slot number. During Fine Tuning, the tuning axis is determined and the magnetic fields are corrected along that axis. In addition, the field integrals in the roll-out location are measured and corrected, as necessary. The Final Measurement phase begins after the tuning process is completed. Its purpose is to document the tuning results and to provide data necessary for understanding the behavior of the undulator during commissioning and operation. 3

4. Tuning Requirements 1. At Tuning Axis *) For radiation wavelength of 1.5 Å 2. At Roll-Out Position (Deviation from Background Fields) 4

5. Tuning Status as of 10/26/2007 SN21: SN22: SN23: On hold … SN24: Tuning and Fiducialization Complete. [13] SN25: Tuning and Fiducialization Complete. [10] SN26: SN27: SN28: SN29: SN30: SN31: SN32: Tuning and Fiducialization Complete. [30] SN33: SN34: SN35: Rough Tuning … SN36: On hold … SN37: Tuning and Fiducialization Complete. [18] SN38: SN39: Fine Tuning … SN40: • SN01: @ANL • SN02: Tuning and Fiducialization Complete. [01] • SN03: Tuning and Fiducialization Complete. [25] • SN04: • SN05: • SN06: On hold … • SN07: Tuning and Fiducialization Complete. [19] • SN08: • SN09: • SN10: • SN11: Tuning and Fiducialization Complete. [03] • SN12: Tuning and Fiducialization Complete. [21] • SN13: Tuning and Fiducialization Complete. [04] • SN14: Tuning and Fiducialization Complete. [09] • SN15: Tuning and Fiducialization Complete. [32] • SN16: • SN17: Tuning and Fiducialization Complete. [02] • SN18: • SN19: Tuning and Fiducialization Complete. [05] • SN20: Tuning and Fiducialization Complete. [33] ref 5

6. Keff well within Tolerance 6

7. Phase Difference well within Tolerance Calculated for E = 13.6 GeV 7

8. On-Axis Field Integrals within Tolerance 8

9. (Earth-Field-Corrected) Roll-Out Field Integrals Too Large Requires Significant Steering Corrections 9

10. First Article Quadrupole Measurements Two first articles of the undulator quadrupoles have been received at Argonne. After initial checks on both magnets at Argonne one was sent to SLAC, the other was kept at Argonne for more detailed magnetic measurements. • The SLAC measurements have been carried out by Scott Anderson from the Metrology group. • Some of those results are presented on the following slides. Photo Mark Jaski 10

11. Undulator Quad Tasks • Vibrating Wire cam mover fixture checked out with Undulator Quad.  • Fiducialize on CMM.  • Measure thermal constants for Quad and Trim coils. • Measure Integrated Gradient of Quad and H-Trim with Stretched Wire System.  • Calibrate Radial Coil using Stretched Wire data.  • Measure Integrated Gradient and Harmonics at specified currents using Radial Coil.  • Measure magnetic center shifts for Quad  & Trim currents and magnet splitting using Radial Coil.  • Fiducialize the quad to the Magnetic Center using Vibrating Wire. Courtesy of Scott Anderson 11

12. Quadrupole Temperature Rise Test at 4 A Data at 4 A Mirror plates on.Ambient = 21.5 ˚C5 Hours ∆T Upper Coil = 6.2 ˚C ∆T Lower Coil = 5.6 ˚C ∆T Outer Steel = 3.4 ˚C ∆T Base = 1 ˚C 12 Courtesy of Scott Anderson

13. Quadrupole Temperature Rise Test at 6 A Data at 6 A Mirror plates on.Ambient = 21.5 ˚C14 hours ∆T Upper Coil = 14 ˚C ∆T Lower Coil = 13 ˚C ∆T Outer Steel = 8 ˚C ∆T Base = 3 ˚C 13 Courtesy of Scott Anderson

14. Quadrupole Temperature Rise Profile Estimates Main Operating Points 14

15. Quadrupole Heating Concerns • The quadrupole steel temperature is elevated by about 7-8 ˚C at regular operating current of 4.5 A. • Indirect heating of adjacent component are being investigated: • Quadrupole Stand • Temperature increase is less than 2 ˚C. Stand expansion will raise quadrupole position. This can be taken into account during alignment. • BPM • Temperature increase of less than 0.5 ˚C has been measured. While a temperature change of that amplitude is a concern, a constant temperature shift is acceptable. • Undulator • Temperature change is still under investigation. • Possibility of temperature gradient along undulator is a concern. • Undulator heating from sources other than the quadrupole (under-girder racks) is being reduced through air flow guiding. 15

16. Stretched Wire Measurements Quad • GL = 3.9671 ± 0.0028 T at 6.00521 ± 0.00002 A • GL/I = 0.6606 ± 0.0005 T/A H-trim • BL/I = 677.9 ± 4.7 µTm/A Good Agreement with requested value of 4 T. Photo Scott Anderson 16

17. Radial Coil Calibrated with Stretched wire. Measures Integrated Gradient and Harmonics. Measures relative changes in magnetic center to less than a micron. Photo Scott Anderson 17

18. Quadruple Harmonics Analysis Slight Coil Misalignment Harmonic amplitudes negligible 18

19. Center Shift vs. Quadrupole Current Y Center Shift vs. Current X Center Shift vs. Current Main Operating Areas±0.9 A × ±2.5 µm 19

20. Center Shift vs. Corrector Current Quadrupole Corrector Test Procedure: Medium Size Corrector Current Loop Large Size Corrector Current Loop • With Corrector Currents set to 0 A, demagnetize quadrupole with main coil. • Set main coils to operating value of 4.5 A. • Set correctors to initial values:0.0 A / 0.0 A for lrge loop0.5 A/ 0.5 A for med loop • Move corrector currents to corners of square and back to initial value and measure magnetic center at each stop. Correctors perform very well. They would be very useful during commissioning and operation. But, presently no budget for power supplies! Rotation due to coil misalignment Hysteresis effects much smaller than expected 20

21. Additional Quadrupole Test • Quadrupole Split Test • X Center shift = 1.27 ± 0.75 µm • Y Center shift = -1.43 ± 0.27 µm • Effect of Mirror Plates on Integrated Gradient • Mirror Plates Installed: GL = 3.9671 ± 0.0028 T • Mirror Plates Removed: GL = 3.9857 ± 0.0028 T • Ratio Remove/Installed: 1.0047 ± 0.0007 21

22. Beam Loss Monitors (BLMs) • Radiation protection of the permanent magnet blocks is very important. • Funds are limited and efforts need to be focused to minimize costs. • A Physics Requirement Document, PRD 1.4-005 has been completed, defining the minimum requirements for the Beam Loss Monitors. 22

23. Beam Loss Monitor Area Coverage • Main purpose of BLM is the protection of undulator magnet blocks. • Less damage expected when segments are rolled-out. • Radiation is expected to peak in beam direction. • One BLM will be positioned in front of each segment. • Its active area will cover the full horizontal width of the magnet blocks • The BLM will be moved with the segment to keep the active BLM area at a fixed relation to the magnet blocks. 23

24. BLM Purpose • The BLM will be used for two purposes • A: Inhibit bunches following an “above-threshold” radiation event. • B: Keep track of the accumulated exposure of the magnets in each undulator. • Purpose A is of highest priority. It will be integrated into the Machine Protection System (MPS) and requires only limited dynamic range from the detectors. • Purpose B is desirable for understanding long-term magnet damage in combination with the undulator exchange program but requires a large dynamic range for the radiation detectors (order 106) and much more sophisticated diagnostics hard and software. 24

25. Additional Loss Monitors • Other Radiation Monitoring Devices • Dosimeters • Located at each undulator. Routinely replaced and evaluated. • Segmented Long Ion Chambers • Investigated • (Quartz)-Fibers • Investigated • Non-Radiative Loss Detectors • Pair of Charge Monitors (Toroids) • One upstream and one downstream of the undulator line • Used in comparator arrangement to detect losses of a few percent • Electron Beam Position Monitors (BPMs) • Continuously calculate trajectory and detect out-of-range situations • Quadrupole Positions and Corrector Power Supply Readbacks • Use deviation from setpoints • Estimate accumulated kicks to backup calculations based on BPMs. 25

26. Summary • Finally got a working design for the undulator vacuum chamber. • Tuning of the first fifteen undulators complete. Results are very encouraging. • A first article quadrupole has been tested and found to meet expected performance. • The Beam Loss Monitor PRD has been completed. Monitor design is under way. 26

27. End of Presentation 27