Undulator Prototype Status and Plans. Marion M. White APS-ASD. Outline – Prototype Undulator Status. Design Challenges Mechanical Design Features Performance Improvements Canted Pole Undulator Measurements Plans Summary. Undulator Design Parameters. LCLS – Familiar Design Challenges.
Marion M. White APS-ASD
Between APS insertion devices and the LEUTL FEL, the APS team has a lot of undulator experience with:
Standard undulator design considerations:
Prevent Radiation Damage
Achieving a field-strength uniformity of 1.5 x 10-4 along the undulator line is a challenge
And there may be a desire to taper in the future
Rails CAM Movers Cradle
Magnetic side shims. Steel bars approach side of pole. Correction up to ~3% in field.
Shims and push-pull screws adjust the gap.
Magnets are clamped from only one side.
Poles have titanium wings, and are clamped on both sides
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.
Each cam is driven by a separate motor
Adjustable in both transverse directions & in roll, pitch, & yaw
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 vendor’s measurements “as is” for sorting; not all vendors routinely make these measurements.
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
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
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.
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°.)
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