October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 1 Undulator Physics Issues Heinz-Dieter Nuhn, SLAC / LCLS October 30, 2007 Vacuum Chamber Update Tuning Status First Article Quadrupole Measurements Beam Loss Monitors Vacuum Chamber Update Tuning Status First Article Quadrupole Measurements Beam Loss Monitors

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

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 3 Tuning Results The procedures for tuning and measuring the LCLS undulator magnets are described in LCLS-TN “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.

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 4 Tuning Requirements 1. At Tuning Axis 2. At Roll-Out Position (Deviation from Background Fields) ParameterTarget ValueToleranceComment K eff See Table  % Effective Undulator parameter I1x0 µTm  40 µTm First Horizontal Field Integral I2x0 µTm 2  50 µTm 2 Second Horizontal Field Integral I1y0 µTm  40 µTm First Vertical Field Integral I2y0 µTm 2  50 µTm 2 Second Vertical Field Integral Total Phase (over m) *) 113 × 360º  10º Total Undulator Segment phase slippage Avg core phase shake *) 0º  10º Average phase deviation along z for core periods RMS core phase shake *) 0º  10º RMS phase deviation along z for core periods *) For radiation wavelength of 1.5 Å ParameterTarget ValueToleranceComment I1x0 µTm  40 µTm First Horizontal Field Integral I2x0 µTm 2  50 µTm 2 Second Horizontal Field Integral I1y0 µTm  40 µTm First Vertical Field Integral I2y0 µTm 2  50 µTm 2 Second Vertical Field Integral

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 5 Tuning Status as of 10/26/2007 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] 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: ref

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 6 K eff well within Tolerance

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 7 Phase Difference well within Tolerance Calculated for E = 13.6 GeV

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 8 On-Axis Field Integrals within Tolerance

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 9 (Earth-Field-Corrected) Roll-Out Field Integrals Too Large Requires Significant Steering Corrections

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 10 First Article Quadrupole 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. 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. Photo Mark Jaski

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

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 12 Quadrupole Temperature Rise Test at 4 A Data at 4 A Mirror plates on. Ambient = 21.5 ˚C 5 Hours ∆T Upper Coil = 6.2 ˚C ∆T Lower Coil = 5.6 ˚C ∆T Outer Steel = 3.4 ˚C ∆T Base = 1 ˚C Data at 4 A Mirror plates on. Ambient = 21.5 ˚C 5 Hours ∆T Upper Coil = 6.2 ˚C ∆T Lower Coil = 5.6 ˚C ∆T Outer Steel = 3.4 ˚C ∆T Base = 1 ˚C Courtesy of Scott Anderson

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 13 Quadrupole Temperature Rise Test at 6 A Data at 6 A Mirror plates on. Ambient = 21.5 ˚C 14 hours ∆T Upper Coil = 14 ˚C ∆T Lower Coil = 13 ˚C ∆T Outer Steel = 8 ˚C ∆T Base = 3 ˚C Data at 6 A Mirror plates on. Ambient = 21.5 ˚C 14 hours ∆T Upper Coil = 14 ˚C ∆T Lower Coil = 13 ˚C ∆T Outer Steel = 8 ˚C ∆T Base = 3 ˚C Courtesy of Scott Anderson

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 14 Quadrupole Temperature Rise Profile Estimates Main Operating Points

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

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 16 Stretched Wire Measurements Quad GL = ± T at ± A GL/I = ± T/A H-trim BL/I = ± 4.7 µTm/A Quad GL = ± T at ± A GL/I = ± T/A H-trim BL/I = ± 4.7 µTm/A Good Agreement with requested value of 4 T. Photo Scott Anderson

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

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 18 Quadruple Harmonics Analysis Slight Coil Misalignment Harmonic amplitudes negligible

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 19 Center Shift vs. Quadrupole Current X Center Shift vs. Current Y Center Shift vs. Current Main Operating Areas ±0.9 A × ±2.5 µm

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 20 Center Shift vs. Corrector Current Large Size Corrector Current Loop Medium Size Corrector Current Loop Rotation due to coil misalignment Hysteresis effects much smaller than expected 1)With Corrector Currents set to 0 A, demagnetize quadrupole with main coil. 2)Set main coils to operating value of 4.5 A. 3)Set correctors to initial values: 0.0 A / 0.0 A for lrge loop 0.5 A/ 0.5 A for med loop 4)Move corrector currents to corners of square and back to initial value and measure magnetic center at each stop. Quadrupole Corrector Test Procedure: Correctors perform very well. They would be very useful during commissioning and operation. But, presently no budget for power supplies!

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 21 Additional Quadrupole Test Quadrupole Split Test X Center shift = 1.27 ± 0.75 µm Y Center shift = ± 0.27 µm Effect of Mirror Plates on Integrated Gradient Mirror Plates Installed: GL = ± T Mirror Plates Removed: GL = ± T Ratio Remove/Installed: ±

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 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 has been completed, defining the minimum requirements for the Beam Loss Monitors. 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 has been completed, defining the minimum requirements for the Beam Loss Monitors.

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

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 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 10 6 ) and much more sophisticated diagnostics hard and software. 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 10 6 ) and much more sophisticated diagnostics hard and software.

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

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

October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues 27 End of Presentation