Undulator Prototype Status and Plans

1
Undulator Prototype Status and Plans

• Marion M. White APS-ASD

2
Outline Prototype Undulator Status

• Design Challenges
• Mechanical Design Features
• Performance
• Improvements
• Canted Pole Undulator Measurements
• Plans
• Summary

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Undulator Design Parameters
Parameter Specified Value
Undulator Type Planar Hybrid
Magnet Material NdFeB
Pole Material Vanadium Permendur
Pole Gap (Min. Allowance) 6 mm
Period Length 30 mm
Effective Magnetic Field 1.296 Tesla
Effective K Value 3.63
Undulator Segment Length 3.40 m
Nr. of Undulator Segments 33
4
LCLS Familiar Design Challenges
Between APS insertion devices and the LEUTL FEL,
the APS team has a lot of undulator experience
with

• High-quality undulator magnetic fields
• Magnetic tuning for phase errors and trajectory
  straightness
• Variable and fixed gaps
• Phasing undulator ends
• Magnetic design
• NdFeB magnets
• Vanadium permendur poles
• 30-mm period
• K3.63 so Beff1.296 T

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Magnetic Design

• Standard undulator design considerations
• Maximize the field
• Dont demagnetize the magnets
• Dont oversaturate the poles

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Magnetic Design (2)
Prevent Radiation Damage

• Chose a new grade of magnet with higher
  coercivity (N39SH) for the prototype
• Attention to minimizing the demagnetizing field
• Design goal to be as restrictive as usual on the
  demagnetizing field, maybe even at the cost of
  higher pole saturation, then use the high Hc
  magnets

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New Challenges Uniformity and Stability

• Achieving a field-strength uniformity of 1.5 x
  10-4 along the undulator line is a challenge
• Gap change of 1.4 microns
• Vertical shift 50 microns
• Temperature coefficient of the magnet is 0.1/C
• Thermal expansion
• And there may be a desire to taper in the future

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Outline Prototype Undulator Status

• Design Challenges
• Mechanical Design Features
• Performance
• Design Improvements
• Canted Pole Measurements
• Plans
• Summary

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Complete Undulator Module
Magnet Assembly
BPM
Quadrupole
Rails CAM Movers
Cradle
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Mechanical Design
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Mechanical Design Features

• Housing is made from a forged Ti bar
• Ti was preferred over other materials because
• Nonmagnetic
• Low thermal expansion
• Long-term stability
• Rigidity to density ratio for minimal deflection
• Al baseplate provides partial thermal
  compensation
• Open on one side for magnetic measurement access
  and shimming

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Titanium Strongback
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Mechanical design features, cont.
Shims and push-pull screws adjust the
gap. Magnets are clamped from only one side.
Magnetic side shims. Steel bars approach side of
pole. Correction up to 3 in field.
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Pole clamping
Poles have titanium wings, and are clamped on
both sides
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Pole simplification now under consideration
Eliminate the wings and screw the pole in from
the bottom. Still being refined will be used in
a segment of the prototype and reviewed.
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End-phase adjusters in the prototype

• Piezo translators on end sections allowed gap
  field strength adjustment
• Over the last seven periods only
• Adjusted phasing between undulators
• Can relax the requirement for constant Beff
  between undulators to 7x10-4
• Travel range 100 micron each jaw (200 microns in
  total gap). 100 microns corresponds to 29.

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Eccentric cam movers
Each cam is driven by a separate motor Adjustable
in both transverse directions in roll, pitch,
yaw
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Outline Prototype Undulator Status

• Design Challenges
• Mechanical Design Features
• Performance
• Design Improvements
• Canted Pole Measurements
• Plans
• Summary

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Assembly - Magnet Sorting
Single Magnets Matched Pairs
Magnets were sorted by strength (Total Moment),
then the strongest and the weakest were matched
together. Very important saved lots of time
since we found we could use this vendors
measurements as is for sorting not all vendors
routinely make these measurements.
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Assembly - pole sorting
After magnet sorting, the main contributor to
field errors was pole height variation. Tall and
short poles were paired, and RMS deviation in gap
was reduced from 6.3 to 2.4 microns
After sorting
But this pairing neglected the contribution of
the Al base plate thickness, and variation due to
the attachment to the Ti. Final gap variation
was 50 microns.
Note Put tighter tolerances on the Al baseplate
for production
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Magnetic Tuning
Nonetheless, the device met the trajectory
straightness requirement (2 micron) without
tuning. After tuning, the wiggle-averaged
trajectory was within a range of about 0.5
microns.
22
Phase Error Tuning
The calculated spontaneous emission amplitude
needed tuning to raise it from 93 to over 99 of
ideal. (The rms phase error decreased from
11.2 to 6.5.)
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Temperature Dependence
Care must be taken in the measurements to allow
the undulator sufficient thermal equilibration
time Also need to correct for temperature
dependence of the Hall probe (DBeff/Beff)/DT
-5.5 x 10-4 /C
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Outline Prototype Undulator Status

• Design Challenges
• Mechanical Design Features
• Performance
• Post-Prototype Design Improvements
• Canted Pole Measurements
• Plans
• Summary

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Post-prototype Considerations

• End phase adjustments
• Piezos long-term stability for this application
  is untested
• Adjustment to final gap has not yet been done,
  but can do this with the cant anyway.
• Assume temperature dependence is handled by the
  conventional facilities specifications.

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Radiation Damage Post-prototype

• Had considered using SmCo magnets
• Better radiation resistance
• Smaller decrease in strength with temperature
  rise
• But overall weaker strength and more brittle
• Ruled out based on schedule no time for RD.
• Instead, take advantage of APS radiation exposure
  and damage experience at the APS.
• Provide dose limit guidance and information to
  SLAC to be used as input into the undulator
  protection system.
• Do not operate LCLS under conditions likely to
  result in damage to the undulators.

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Post-prototype, cont.

• A comb shunt for adjusting the field strength was
  proposed
• Initial tests look promising, but added design
  complexity (remote capability - considerable
  added design complexity)
• Also a possibility for end phase correction only

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Outline Prototype Undulator Status

• Design Challenges
• Mechanical Design Features
• Performance
• Post-Prototype Design Improvements
• Canted Pole Measurements
• Plans
• Summary

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Canting The Gap

• A scheme ( thanks to J. Pflueger) of canting the
  poles so that field strength varies with lateral
  (horizontal) position was very promising.
• A test section was canted and measured with
  excellent results. Canting was adopted into the
  baseline.

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Canted Cross-section (exaggerated)
LCLS Undulator Cross- Section with Wedged
Shims
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Effective Magnetic Field

• Measured slope of 6.6 Gauss/mm agrees with
  calculations ( 5.7 Gauss/mm for 3 mrad cant).
• Alignment accuracy needed for DB/B 1.5x10-4 2
  Gauss -gt 0.3 mm

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RMS Phase Error

• No significant dependency on X
• An RMS phase error of 6.5 degree is an upper
  limit for near-perfect (100) performance.

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Horizontal Trajectory (averaged over period
length) at 14.1 GeV

• Trajectory vs. X well behaved and well within the
  tolerance requirement of 2 mm maximum walk-off
  from a straight line.
• Operational range is 1.2 mm for 1.0C
  temperature compensation.

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Fringe Fields at X65 and 100 mm

• Fringe fields with new shims are close to earth
  field for X100 mm. (Earth field contribution to
  trajectory shift has to be corrected.)

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Fine adjustment of effective magnetic
field(Isaacs field-tuning procedure )

1. Select spacers with thickness step 15 µm to set
   the effective field in the range of 30 Gauss (1
   µm in gap corresponds to 2 Gauss in field).
2. Set spacer horizontal position to adjust the
   effective field to 6 Gauss (spacers are wedged
   with 3 mm/mm cant)
3. Set horizontal position of the undulator as a
   whole so the effective field is in the range 2
   Gauss (DB/B 1.5x10-4) (This step saves time
   and provides better accuracy)
4. The undulator horizontal position could be
   remotely controlled during operation to
   compensate for in-tunnel temperature variations
   (motion of 1.2 mm for 1C needed). Such option
   is available, if quadrupoles are separated from
   undulator sections.

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Magnetic needles for alignment

• Only one needle is required for alignment in the
  X direction
• One more needle has to be added at Y0 for
  alignment in the Y direction

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Outline Prototype Undulator Status

• Design Challenges
• Mechanical Design Features
• Performance
• Post-Prototype Design Improvements
• Canted Pole Measurements
• Plans
• Summary

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Scope and Plans Undulator Systems

• 33 Precision magnetic arrays with canted poles
• 33 Support/alignment systems including
• Cradle that supports the undulator, BPM, and
  quadrupole magnet.
• Precision CAM movers and motors enabling
  positioning, alignment, and adjustment of the
  cradle.
• Rail system to move the undulator, facilitating
  manual retraction of an undulator out of the
  beamline and precision reproducible re-insertion.
• 7 Spare Undulator Modules
• 1 Undulator Transport Device for Installation

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Plan Undulators (1)

• To meet schedule and funding profiles, and to
  ensure that the Undulator Systems are complete by
  July 2007, we plan to procure the following
  long-lead items as early as possible in FY05
• Precision-machined titanium strongbacks
• NdFeB Magnet blocks
• Vanadium Permendur Magnet poles
• The same APS undulator experts, who were relied
  upon for design, construction, and assessment of
  the prototype, will finalize procurement packages
  for the LL items, in accordance with our Advance
  Procurement Plans APP.

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Scope Quadrupole Magnet Systems

• 33 Quadrupole Magnet Systems - installed
• Permanent Magnet Quadrupole
• Support with Precision Translator settable to 5
  um readout to 1um
• 5 Spare Magnet Systems
• Separate steering is not included

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Summary

• A full-scale prototype undulator was constructed
  and tested at APS, and met LCLS performance
  goals.
• A subsequent design improvement, that of
  introducing a 3-mrad cant in the pole gap, was
  implemented using wedged spacers between the
  aluminum base plates and the titanium core. It
  was successfully tested and the concept was
  adopted in the baseline.
• A disadvantage of the canted-pole design is the
  necessity to provide a separate support for
  vacuum chamber
• Magnetic measurements show good agreement with
  calculated change of the effective magnetic field
  versus X (horizontal motion).
• No significant change of the RMS phase error
  versus X was measured.

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Current Status

• Significant effort has been devoted to planning,
  resulting in a detailed undulator construction
  schedule that is integrated with the BPM,
  quadrupole and vacuum chamber construction and
  testing. The undulator schedule and the magnet
  measurement schedule are mostly integrated, and
  are consistent with completion of undulator
  systems in July 2007.
• A skeleton installation schedule exists details
  are being added and integration with the rest of
  the schedule is ongoing.
• Schedule refinement is ongoing.
• Costs were estimated by in-house experts with
  relevant experience and were based on vendor
  quotes and previous experience. Cost scrubbing
  will continue.
• The greatest schedule risks come from
• Design changes
• Delayed funding