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

1October 30, 2007 Heinz-Dieter Nuhn, SLAC / LCLSUndulator Physics Issues [email protected]

Undulator Physics IssuesHeinz-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


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.


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.


Tuning Requirements

1. At Tuning Axis

2. At Roll-Out Position (Deviation from Background Fields)

Parameter Target Value Tolerance Comment

Keff See Table 0.015 % Effective Undulator parameter

I1x 0 µTm 40 µTm First Horizontal Field Integral

I2x 0 µTm2 50 µTm2 Second Horizontal Field Integral

I1y 0 µTm 40 µTm First Vertical Field Integral

I2y 0 µTm2 50 µTm2 Second Vertical Field Integral

Total Phase (over 3.656 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

Parameter Target Value Tolerance Comment

I1x 0 µTm 40 µTm First Horizontal Field Integral

I2x 0 µTm2 50 µTm2 Second Horizontal Field Integral

I1y 0 µTm 40 µTm First Vertical Field Integral

I2y 0 µTm2 50 µTm2 Second Vertical Field Integral


Tuning Status as of 10/26/2007

SN01: @ANLSN02: 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


Keff well within Tolerance


Phase Difference well within Tolerance

Calculated for E = 13.6 GeV


On-Axis Field Integrals within Tolerance


(Earth-Field-Corrected) Roll-Out Field Integrals Too Large

Requires Significant Steering CorrectionsRequires Significant Steering Corrections


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


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 AndersonCourtesy of Scott Anderson


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

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



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

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



Quadrupole Temperature Rise Profile Estimates

Main Operating Points Main Operating Points


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 StandTemperature increase is less than 2 ˚C. Stand expansion will raise quadrupole position. This can be taken into account during alignment.

BPMTemperature 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.

UndulatorTemperature 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.


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

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. Good Agreement with requested value of 4 T.

Photo Scott Anderson


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


Quadruple Harmonics Analysis

Slight Coil Misalignment Slight Coil Misalignment

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Center Shift vs. Quadrupole Current

X Center Shift vs. CurrentX Center Shift vs. Current Y Center Shift vs. CurrentY Center Shift vs. Current

Main Operating Areas±0.9 A × ±2.5 µm

Main Operating Areas±0.9 A × ±2.5 µm


Center Shift vs. Corrector Current

Large Size Corrector Current LoopLarge Size Corrector Current Loop Medium Size Corrector Current LoopMedium Size Corrector Current Loop

Rotation due to coil misalignment Rotation due to coil misalignment Hysteresis effects much smaller than expected 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 loop0.5 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!


Additional Quadrupole Test

Quadrupole Split TestX Center shift = 1.27 ± 0.75 µm

Y Center shift = -1.43 ± 0.27 µm

Effect of Mirror Plates on Integrated GradientMirror Plates Installed: GL = 3.9671 ± 0.0028 T

Mirror Plates Removed: GL = 3.9857 ± 0.0028 T

Ratio Remove/Installed: 1.0047 ± 0.0007


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.

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.


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 blocksThe 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 blocksThe BLM will be moved with the segment to keep the active BLM area at a fixed relation to the magnet blocks.


BLM Purpose

The BLM will be used for two purposesA: 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.

The BLM will be used for two purposesA: 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.


Additional Loss Monitors

Other Radiation Monitoring DevicesDosimeters

Located at each undulator. Routinely replaced and evaluated.

Segmented Long Ion ChambersInvestigated

(Quartz)-FibersInvestigated

Non-Radiative Loss DetectorsPair of Charge Monitors (Toroids)

One upstream and one downstream of the undulator lineUsed 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 ReadbacksUse deviation from setpointsEstimate accumulated kicks to backup calculations based on BPMs.


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.


End of Presentation

Documents

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