April 16, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues [email protected] 1 Undulator Physics Issues Heinz-Dieter Nuhn, SLAC / LCLS

1April 16, 2007 Heinz-Dieter Nuhn, SLAC / LCLSUndulator Physics Issues [email protected]

Undulator Physics IssuesHeinz-Dieter Nuhn, SLAC / LCLS

April 16, 2007

Vacuum Chamber Update

Tuning Results

Undulator Pole Tip Locations

Beam Loss Monitors


Tuning Results


Beam Loss Monitors



The vacuum chamber is making progress.

The two competing designs (ANL vs SLAC) have been reviewed on February 22.

LCLS management has chosen the ANL design.

A ‘ready-to-install’ prototype had been completed by the review.

Vacuum tests were completed with good result.

The chamber has been cut to produce samples for permeability and roughness measurements of the coated surface.

Theses measurements have not yet been completed.

The vacuum chamber is making progress.

The two competing designs (ANL vs SLAC) have been reviewed on February 22.

LCLS management has chosen the ANL design.

A ‘ready-to-install’ prototype had been completed by the review.

Vacuum tests were completed with good result.

The chamber has been cut to produce samples for permeability and roughness measurements of the coated surface.

Theses measurements have not yet been completed.


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

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 ~100 µTm 40 µTm First Horizontal Field Integral

I2x ~200 µTm2 50 µTm2 Second Horizontal Field Integral

I1y ~100 µTm 40 µTm First Vertical Field Integral

I2y ~120 µTm 50 µTm2 Second Vertical Field Integral


Present Tuning Status

1. Serial Number: L143-112000-02 [Slot: 01]Rough Tuning: CompleteFine Tuning: Complete



4. Serial Number: L143-112000-06 [Slot: ] [Larger than expected matching errors]Rough Tuning: CompleteFine Tuning: In Progress

5. Serial Number: L143-112000-11 [Slot: 04]Rough Tuning: CompleteFine Tuning: -

6. Serial Number: L143-112000-13 [Slot: ]Rough Tuning: In ProgressFine Tuning: -


Measured Keff vs x for SN02

Target Keff = 3.5

Fit:

Keff=K0+K1x+K2x2+K3x3

K0 = 3.500077

K1 = 0.002754

K2 = -0.000017

K3 = -0.000002

(1/B0) dB/dx =

0.0787 %/mm

Estimated cant angle:

5.4 mrad

Target Keff = 3.5

Fit:

Keff=K0+K1x+K2x2+K3x3

K0 = 3.500077

K1 = 0.002754

K2 = -0.000017

K3 = -0.000002

(1/B0) dB/dx =

0.0787 %/mm

Estimated cant angle:

5.4 mrad


Measured Phase Shake through LCLS Undulator SN02

<> = 0.00º<>)rms = 3.66º

Wiggler Period Averaged Spec Range

RMS Deviation

E: 13.64 GeV

Undulator Average


First Bx Field Integral Measurements


Change of Bx Shim Design

Original shim design used in SN02 and SN03.

New shim design used in SN17 and SN06 so far.

Original shim design used in SN02 and SN03.

New shim design used in SN17 and SN06 so far.


Second Bx Field Integral Measurements


First By Field Integral Measurements


Second By Field Integral Measurements


Measured Roll-Out Trajectory for LCLS Undulator SN02

E: 13.64 GeV

Upper: Horizontal

<x> = 4.01 µm

(x)rms= 3.26 µm

I1y: 71.7 µTm

I2y: 433.6 µTm2

Lower: Vertical

<y> = -1.27 µm

(y)rms= 1.42 µm

I1x: -128.9 µTm

I2x -220.4 µTm2

E: 13.64 GeV

Upper: Horizontal

<x> = 4.01 µm

(x)rms= 3.26 µm

I1y: 71.7 µTm

I2y: 433.6 µTm2

Lower: Vertical

<y> = -1.27 µm

(y)rms= 1.42 µm

I1x: -128.9 µTm

I2x -220.4 µTm2

Undulator AverageRMS Deviation


Earth Field Corrected Roll-Out Trajectory for LCLS Undulator SN02

E: 13.64 GeV

Upper: Horizontal

<x> = 2.89 µm

(x)rms= 2.28 µm

I1y: 0.0 µTm

I2y: 281.3 µTm2

Lower: Vertical

<y> = 0.75 µm

(y)rms= 0.48 µm

I1x: 0.0 µTm

I2x 53.4 µTm2

E: 13.64 GeV

Upper: Horizontal

<x> = 2.89 µm

(x)rms= 2.28 µm

I1y: 0.0 µTm

I2y: 281.3 µTm2

Lower: Vertical

<y> = 0.75 µm

(y)rms= 0.48 µm

I1x: 0.0 µTm

I2x 53.4 µTm2

Undulator Average

RMS Deviation



The geometrical position of the pole faces is being measured in the MMF on the CMM as the magnets arrive at SLAC.

Unexpectedly large distributions of per-pole as well as undulator-averaged values were found for the following mechanical dimensions:

Cant Angles

Gap Heights

Vertical Mid-Plane Positions

The geometrical position of the pole faces is being measured in the MMF on the CMM as the magnets arrive at SLAC.

Unexpectedly large distributions of per-pole as well as undulator-averaged values were found for the following mechanical dimensions:

Cant Angles

Gap Heights

Vertical Mid-Plane Positions


Cant Angles Distributions for SN03


Cant Angle Measurements

RMS Spread over 226 poles


Pole Tip Locations for SN03

Quasi-periodic gap-height variations

85 µm

Overall mid-plane sag

106 µm

Quasi-periodic gap-height variations

85 µm

Overall mid-plane sag

106 µm


Undulator Pole Tip Locations Summaries

Very close to the 6.8 mm minimum required to insert the vacuum chamber.Very close to the 6.8 mm minimum required to insert the vacuum chamber.


Undulator Pole Tip Locations Summary

Most of the effects of the unexpectedly large distributions of per-pole as well as undulator-averaged values for cant angles, gap heights, and mid-plane-positions can be compensated in the tuning process.

Presently, only the larger than expected cant angles will have remnant effect. They require a reduction of the horizontal alignment tolerance from 140 microns.

Most of the effects of the unexpectedly large distributions of per-pole as well as undulator-averaged values for cant angles, gap heights, and mid-plane-positions can be compensated in the tuning process.

Presently, only the larger than expected cant angles will have remnant effect. They require a reduction of the horizontal alignment tolerance from 140 microns.


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 is being written to define the minimum requirements.

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 is being written to define the minimum requirements.


Estimated Radiation-Based Magnet Damage

The loss of magnetization caused by a given amount of radiation has been estimated by Alderman et al. [[i]].

Their results imply that a 0.01% loss in magnetization occurs after absorption of a total fast-neutron fluence of 1011 neutrons/cm2.

Recent measurements by Sasaki et al. at the APS (published in PAC 05) question those findings of the importance of the neutron flux.

[i] J. Alderman, et. A., Radiation Induced Demagnetization of Nd-Fe-B Permanent Magnets, Advanced Photon Source Report LS-290 (2001)

The loss of magnetization caused by a given amount of radiation has been estimated by Alderman et al. [[i]].

Their results imply that a 0.01% loss in magnetization occurs after absorption of a total fast-neutron fluence of 1011 neutrons/cm2.

Recent measurements by Sasaki et al. at the APS (published in PAC 05) question those findings of the importance of the neutron flux.

[i] J. Alderman, et. A., Radiation Induced Demagnetization of Nd-Fe-B Permanent Magnets, Advanced Photon Source Report LS-290 (2001)


Estimate of Neutron Fluences

The radiation deposited in the permanent magnets blocks of the LCLS undulator, when a single electron (e-) strikes a 100-µm carbon foil upstream of the first undulator, has been simulated by A. Fasso [[i]].The results are a peak total dose of about 1.0×10-9 rad/e- including a neutron (n) fluence of 1.8×10-4 n/cm2/e-. This translates into 1.8×105 n/cm2 for each rad of absorbed energy.These numbers are based on peak damage situations and should therefore be considered as worst case estimates.

[i] A. Fasso, Dose Absorbed in LCLS Undulator Magnets, I. Effect of a 100 µm Diamond Profile Monitor, RP-05-05, May 2005.

The radiation deposited in the permanent magnets blocks of the LCLS undulator, when a single electron (e-) strikes a 100-µm carbon foil upstream of the first undulator, has been simulated by A. Fasso [[i]].The results are a peak total dose of about 1.0×10-9 rad/e- including a neutron (n) fluence of 1.8×10-4 n/cm2/e-. This translates into 1.8×105 n/cm2 for each rad of absorbed energy.These numbers are based on peak damage situations and should therefore be considered as worst case estimates.

[i] A. Fasso, Dose Absorbed in LCLS Undulator Magnets, I. Effect of a 100 µm Diamond Profile Monitor, RP-05-05, May 2005.


Simulated Neutron Fluences

Simulated neutron fluences in the LCLS undulator magnets (upper Yaw) from a single electron hitting a 100 micron thick carbon foil upstream of the first undulator.

Maximum Level is

1.8×10-4 n/cm2/e-

Simulated neutron fluences in the LCLS undulator magnets (upper Yaw) from a single electron hitting a 100 micron thick carbon foil upstream of the first undulator.

Maximum Level is

1.8×10-4 n/cm2/e-

A. FassoA. Fasso


Total Dose from e- hitting a Carbon Foil

Corresponding maximum deposited dose.

Maximum Level is

1.0×10-9 rad/e-

Corresponding maximum deposited dose.

Maximum Level is

1.0×10-9 rad/e-

A. FassoA. Fasso


Radiation Limit Estimates

Neutron fluence for 0.01 % magnet damage from Alderman et al. 1×1011 n/cm2

Maximum neutron fluence in LCLS magnets from hit on 100 micron C foil from Fasso 1.8×10-4 n/cm2/e-

Maximum total dose in LCLS magnets from hit on 100 micron carbon foil from Fasso 1×10-9 rad/e-

Ratio of neutron fluence per total dose 1.8×105 n/cm2/rad

Maximum total dose in LCLS magnets for 0.01 % damage 5.5×105 rad

Nominal LCLS lifetime 20 years

Number of seconds in 20 years 6.3×108 s

Maximum average permissible energy deposit per magnet 8.8×10-4 rad/s

Corresponding per pulse dose limit during 120 Hz operation 7.3 µrad/pulse


Maximum Estimated Radiation Dose from BFW Operation

Maximum neutron fluence in LCLS magnets due to BFW hit; All undulators rolled-in;

from Welch based on Fasso.

Total Charge: 1 nC; Wire Material: C; Wire Diameter 40 µm; RMS Beam radius 37 µm;

1.5×105 n/cm2/pulse

Radiation dose corresponding to BFW hit 0.85 rad/pulse

Ratio of peak required dose to maximum average dose 1.8×105

Ratio for 0.1 nC charge 1.8×104

Ratio for 0.1 nC charge and down-stream undulators rolled-out

(assuming factor 100 reduction)

1.8×102


Radiation Sources

BFW operationIs expected to produce the highest levels. May only be allowable when all down-stream undulators are rolled-out and beam charge is reduced to minimum.

Foil insertionMay only be allowable when all undulators are rolled-out and beam charge is reduced to minimum.

Background radiationCurrently not known.Radiation levels potentially higher than maximum desirable per-pulse dose.BLMs could get saturated from non-demagnetizing radiation component

Beam HaloExpected to be sufficiently suppressed through collimator system.May require halo detection system.

Beam MissteeringWill be caught by BCS and will lead to beam abort.


Detector Considerations

One BLM device will be mounted upstream of each Undulator Segment with 2 sensitivity around beam pipe.The BLM will provide a signal proportional to the amount of energy deposited in the device for each electron bunch.The BLM shall be able to detect and precisely (1%) measure radiation levels corresponding to magnet dose levels as low as 0.01 mrad/pulse and up to the maximum expected level of 10 mrad/pulse.The BLM needs to be designed to withstand the highest expected radiation levels without damage. The radiation level received from each individual electron bunch needs to be reported within 1 msec after the passage of that bunch. The following additional detectors are under consideration:

Halo detector after last undulator.Integrating fiber installation in first segments for investigational purposes.Dosimeters mounted on the front faces of the Undulator Strongbacks.


Detector Calibration

Beam Loss Monitor Calibration will be based on well defined calibration events.A single pulse of known charge hitting a BFW wire or an upstream foil.

The events will be simulated by Radiation Physics.

The simulations will yieldNeutron fluence levels in the magnets

Dose levels in the detectors

The measured detector voltages will be calibrated with the simulated radiation levels.


Machine Protection System Requirements

The Beam Protection system (MPS) will use the signal from the BLM immediately preceding an Undulator Segment together with the roll-in/out status of that Undulator Segment after the expected passage of each electron bunch to calculate the incremental dose received by the magnets of that Undulator Segment.

The MPS for the Undulator System will run in one of three beam modes:

(1) Single Shot,

(2) Recovery

(3) Standard.

The estimated magnet dose will be used to control running parameters.


Summary

Significant progress in the vacuum chamber development occurred since the last FAC. Still waiting for the final surface roughness and permeability measurements.

Mechanical dimensions of the undulators show fairly large spread. Tuning can compensate for most of it. Larger than expected can angles require reduction in horizontal alignment tolerance.

Tuning of the first three undulators complete. Results are very encouraging. A modification in the Bx shim design appears to reduce the harmonics in the field integrals.

The Beam Loss Monitor requirements are reexamined to derive minimum requirements in order to reduce costs.


End of Presentation

Documents

April 16, 2007 Heinz-Dieter Nuhn, SLAC / LCLS Undulator Physics Issues [email protected] 1 Undulator Physics Issues Heinz-Dieter Nuhn, SLAC / LCLS