Transcript Undulator Physics Issues

Undulator Physics Issues
Heinz-Dieter Nuhn, SLAC / LCLS
April 16, 2007
Vacuum Chamber Update
Tuning Results
Undulator Pole Tip Locations
Beam Loss Monitors
April 16, 2007
Undulator Physics Issues
1
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Vacuum Chamber Update
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.
April 16, 2007
Undulator Physics Issues
2
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
April 16, 2007
Undulator Physics Issues
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Tuning Requirements
1. At Tuning Axis
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
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
Total Phase (over 3.656 m)*)
*) For radiation wavelength of 1.5 Å
2. At Roll-Out Position
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
April 16, 2007
Undulator Physics Issues
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Present Tuning Status
1.
Serial Number: L143-112000-02 [Slot: 01]
Rough Tuning: Complete
Fine Tuning: Complete
2.
Serial Number: L143-112000-03 [Slot: 25]
Rough Tuning: Complete
Fine Tuning: Complete
3.
Serial Number: L143-112000-17 [Slot: 02]
Rough Tuning: Complete
Fine Tuning: Complete
4.
Serial Number: L143-112000-06 [Slot: ] [Larger than expected matching errors]
Rough Tuning: Complete
Fine Tuning: In Progress
5.
Serial Number: L143-112000-11 [Slot: 04]
Rough Tuning: Complete
Fine Tuning: -
6.
Serial Number: L143-112000-13 [Slot: ]
Rough Tuning: In Progress
Fine Tuning: -
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Measured Phase Shake through LCLS Undulator SN02
E: 13.64 GeV
<Df> = 0.00º
(Df-<Df>)rms = 3.66º
Wiggler Period Averaged
Spec Range
RMS Deviation
Undulator Average
April 16, 2007
Undulator Physics Issues
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
First Bx Field Integral Measurements
April 16, 2007
Undulator Physics Issues
8
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Change of Bx Shim Design
Original shim design
used in SN02 and
SN03.
New shim design
used in SN17 and
SN06 so far.
April 16, 2007
Undulator Physics Issues
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Second Bx Field Integral Measurements
April 16, 2007
Undulator Physics Issues
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
First By Field Integral Measurements
April 16, 2007
Undulator Physics Issues
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Second By Field Integral Measurements
April 16, 2007
Undulator Physics Issues
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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
April 16, 2007
Undulator Physics Issues
Undulator Average
13
RMS Deviation
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Earth Field Corrected Roll-Out Trajectory for LCLS Undulator SN02
E: 13.64 GeV
Upper: Horizontal
<Dx> = 2.89 µm
(Dx)rms= 2.28 µm
DI1y:
0.0 µTm
DI2y: 281.3 µTm2
Lower: Vertical
<Dy> = 0.75 µm
(Dy)rms= 0.48 µm
DI1x:
0.0 µTm
DI2x
53.4 µTm2
April 16, 2007
Undulator Physics Issues
Undulator Average
RMS Deviation
14
Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Undulator Pole Tip Locations
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
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Cant Angles Distributions for SN03
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Cant Angle Measurements
RMS Spread over 226 poles
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Pole Tip Locations for SN03
Quasi-periodic
gap-height
variations
85 µm
Overall mid-plane
sag
106 µm
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Undulator Pole Tip Locations Summaries
Very close to the 6.8 mm minimum required to insert the vacuum chamber.
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Undulator Pole Tip Locations Summary
Most of the effects of the unexpectedly large
distributions of per-pole as well as undulatoraveraged 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.
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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)
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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/eincluding 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.
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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-
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Heinz-Dieter Nuhn, SLAC
/ LCLS
A. Fasso
[email protected]
Total Dose from e- hitting a Carbon Foil
Corresponding maximum
deposited dose.
Maximum Level is
1.0×10-9 rad/e-
April 16, 2007
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Heinz-Dieter Nuhn, SLAC
/ LCLS
A. Fasso
[email protected]
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
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Radiation Sources
BFW operation
Is 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 insertion
May only be allowable when all undulators are rolled-out and beam charge
is reduced to minimum.
Background radiation
Currently not known.
Radiation levels potentially higher than maximum desirable per-pulse dose.
BLMs could get saturated from non-demagnetizing radiation component
Beam Halo
Expected to be sufficiently suppressed through collimator system.
May require halo detection system.
Beam Missteering
Will be caught by BCS and will lead to beam abort.
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Detector Considerations
One BLM device will be mounted upstream of each Undulator
Segment with 2p 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.
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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 yield
Neutron fluence levels in the magnets
Dose levels in the detectors
The measured detector voltages will be calibrated with the simulated radiation
levels.
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
Machine Protection System Requirements
The Beam Protection system (MPS) will use the signal from the BLM
immediately preceding an Undulator Segment together with the rollin/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.
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
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.
April 16, 2007
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]
End of Presentation
April 16, 2007
Undulator Physics Issues
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Heinz-Dieter Nuhn, SLAC / LCLS
[email protected]