A U.S. Department of Energy Office of Science Laboratory Operated by The University of Chicago Argonne National Laboratory Office of Science U.S. Department of Energy First Prototype Report Summary Elizabeth Moog LCLS Undulator System Review March 3-4, 2004

Pioneering Science and Technology Office of Science U.S. Department of Energy 2 Familiar challenges Between the APS insertion devices and the LEUTL FEL, many challenges were already known High-quality undulator magnetic field Magnetic tuning for phase errors and trajectory straightness Variable and fixed gap Phasing undulator ends Magnetic design -NdFeB magnets -Vanadium permendur poles -30 mm period -K=3.71 so B eff =1.325 T

Pioneering Science and Technology Office of Science U.S. Department of Energy 3 Magnetic design Standard undulator design considerations Maximize field Don’t demagnetize magnets Don’t oversaturate poles Radiation damage prevention Choose new grade of magnet with higher coercivity (N39SH) Attention to minimizing demag field Design goal to be as restrictive as usual on demag field, maybe even at the cost of higher pole saturation, then use high H c magnets

Pioneering Science and Technology Office of Science U.S. Department of Energy 4 New challenges Uniformity of field strength along undulator line of 1.5 x is a challenge Gap change of 1.4 microns Vertical shift ~ 50 microns Temp coefficient of magnet is 0.1%/°C Thermal expansion And there might be a desire to taper in the future

Pioneering Science and Technology Office of Science U.S. Department of Energy 5 Mechanical design

Pioneering Science and Technology Office of Science U.S. Department of Energy 6 Mechanical design features Housing made from a forged Ti bar Other materials considered, but Ti chosen Nonmagnetic Low thermal expansion Long-term stability Rigidity to density ratio Al baseplate for partial thermal compensation Open on side for magnetic measurement access and shimming

Pioneering Science and Technology Office of Science U.S. Department of Energy 7 Mechanical design features, cont. Shims and push-pull screws to adjust gap Magnets clamped from only one side Magnetic side shims. Steel bars approach side of pole. Correction up to ~3% in field.

Pioneering Science and Technology Office of Science U.S. Department of Energy 8 Pole clamping Poles have wings of Ti Poles originally held with one clamp Design later changed to add second clamp

Pioneering Science and Technology Office of Science U.S. Department of Energy 9 End-phase adjusters Piezo translators on end sections allow adjustment of gap & field strength Last seven periods only Adjusts phasing between undulators Can relax the requirement for constant B eff between undulators to 7x10 -4 Travel range 100 micron each jaw (200 microns in total gap). 100 microns corresponds to 29°.

Pioneering Science and Technology Office of Science U.S. Department of Energy 10 Eccentric cam movers Each cam is driven by a separate motor Adjustable in both transverse directions & in roll, pitch & yaw

Pioneering Science and Technology Office of Science U.S. Department of Energy 11 Assembly - magnet sorting Magnets were sorted by strength - match strongest & weakest Measurements approximating the 2nd field integral of each pair were made. Pairs were swapped to smooth the trajectory.

Pioneering Science and Technology Office of Science U.S. Department of Energy 12 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.

Pioneering Science and Technology Office of Science U.S. Department of Energy 13 Magnetic tuning Nonetheless, the device met the trajectory straightness requirement (±2 micron) without tuning. After tuning, the wiggle-averaged trajectory was within about 0.5 micron range.

Pioneering Science and Technology Office of Science U.S. Department of Energy 14 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°.)

Pioneering Science and Technology Office of Science U.S. Department of Energy 15 Temperature dependence Care must be taken in the measurements to allow sufficient thermal equilibration time Need to correct for temperature dependence of Hall probe (  B eff /B eff )/  T = -5.5 x /°C

Pioneering Science and Technology Office of Science U.S. Department of Energy 16 Still discussed after prototype SmCo magnets -Better radiation resistance -Smaller decrease in strength with temperature rise -But weaker strength and more brittle -Ruled out based on schedule. Make beam behave instead. End phase adjustments -Piezos are expensive and their long-term stability untested Adjustment to final gap has not yet been done Need manual method for aligning undulator segments Better pole gap uniformity would reduce initial field errors How will temperature dependence be handled? Will there be some provision for tapering?

Pioneering Science and Technology Office of Science U.S. Department of Energy 17 Still discussed, cont. A comb shunt for adjusting the field strength was proposed Initial tests looked promising Also a possibility for end phase correction only

Pioneering Science and Technology Office of Science U.S. Department of Energy 18 Canting the gap A scheme involving canting the poles so the field strength varies with lateral (horizontal) position looks promising Isaac Vasserman will discuss that