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 Undulator Prototype Status and Plans Marion M. White APS-ASD

Pioneering Science and Technology Office of Science U.S. Department of Energy 2 Outline – Prototype Undulator Status Design Challenges Mechanical Design Features Performance Improvements Canted Pole Undulator Measurements Plans Summary

Pioneering Science and Technology Office of Science U.S. Department of Energy 3 Undulator Design Parameters ParameterSpecified Value Undulator TypePlanar Hybrid Magnet MaterialNdFeB Pole MaterialVanadium Permendur Pole Gap (Min. Allowance)6 mm Period Length30 mm Effective Magnetic Field1.296 Tesla Effective K Value3.63 Undulator Segment Length3.40 m Nr. of Undulator Segments33

Pioneering Science and Technology Office of Science U.S. Department of Energy 4 LCLS – Familiar Design Challenges 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 -K=3.63 so B eff =1.296 T Between APS insertion devices and the LEUTL FEL, the APS team has a lot of undulator experience with:

Pioneering Science and Technology Office of Science U.S. Department of Energy 5 Magnetic Design Standard undulator design considerations: Maximize the field Don’t demagnetize the magnets Don’t oversaturate the poles

Pioneering Science and Technology Office of Science U.S. Department of Energy 6 Magnetic Design (2) -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 H c magnets Prevent Radiation Damage

Pioneering Science and Technology Office of Science U.S. Department of Energy 7 New Challenges – Uniformity and Stability Achieving a field-strength uniformity of 1.5 x 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

Pioneering Science and Technology Office of Science U.S. Department of Energy 8 Outline – Prototype Undulator Status Design Challenges Mechanical Design Features Performance Design Improvements Canted Pole Measurements Plans Summary

Pioneering Science and Technology Office of Science U.S. Department of Energy 9 Complete Undulator Module Magnet Assembly BPM Quadrupole Rails CAM Movers Cradle

Pioneering Science and Technology Office of Science U.S. Department of Energy 10 Mechanical Design

Pioneering Science and Technology Office of Science U.S. Department of Energy 11 Mechanical Design Features 1.Housing is made from a forged Ti bar 2.Ti was preferred over other materials because: Nonmagnetic Low thermal expansion Long-term stability Rigidity to density ratio for minimal deflection 3.Al baseplate provides partial thermal compensation 4.Open on one side for magnetic measurement access and shimming

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

Pioneering Science and Technology Office of Science U.S. Department of Energy 13 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.

Pioneering Science and Technology Office of Science U.S. Department of Energy 14 Pole clamping Poles have titanium wings, and are clamped on both sides

Pioneering Science and Technology Office of Science U.S. Department of Energy 15 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.

Pioneering Science and Technology Office of Science U.S. Department of Energy 16 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 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 17 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 18 Outline – Prototype Undulator Status Design Challenges Mechanical Design Features Performance Design Improvements Canted Pole Measurements Plans Summary

Pioneering Science and Technology Office of Science U.S. Department of Energy 19 Assembly - Magnet Sorting 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. Single Magnets Matched Pairs

Pioneering Science and Technology Office of Science U.S. Department of Energy 20 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

Pioneering Science and Technology Office of Science U.S. Department of Energy 21 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.

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

Pioneering Science and Technology Office of Science U.S. Department of Energy 23 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: (  B eff /B eff )/  T = -5.5 x /°C

Pioneering Science and Technology Office of Science U.S. Department of Energy 24 Outline – Prototype Undulator Status Design Challenges Mechanical Design Features Performance Post-Prototype Design Improvements Canted Pole Measurements Plans Summary

Pioneering Science and Technology Office of Science U.S. Department of Energy 25 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.

Pioneering Science and Technology Office of Science U.S. Department of Energy 26 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 R&D. 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.

Pioneering Science and Technology Office of Science U.S. Department of Energy 27 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

Pioneering Science and Technology Office of Science U.S. Department of Energy 28 Outline – Prototype Undulator Status Design Challenges Mechanical Design Features Performance Post-Prototype Design Improvements Canted Pole Measurements Plans Summary

Pioneering Science and Technology Office of Science U.S. Department of Energy 29 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.

Pioneering Science and Technology Office of Science U.S. Department of Energy 30 Canted Cross-section (exaggerated) LCLS Undulator Cross- Section with Wedged Shims

Pioneering Science and Technology Office of Science U.S. Department of Energy 31 Measured slope of 6.6 Gauss/mm agrees with calculations (~ 5.7 Gauss/mm for 3 mrad cant). Alignment accuracy needed for  B/B ~ 1.5x10 -4 ~ 2 Gauss -> 0.3 mm Effective Magnetic Field

Pioneering Science and Technology Office of Science U.S. Department of Energy 32 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.

Pioneering Science and Technology Office of Science U.S. Department of Energy 33 Horizontal Trajectory (averaged over period length) at 14.1 GeV Trajectory vs. X well behaved and well within the tolerance requirement of 2  m maximum walk-off from a straight line. Operational range is ±1.2 mm for ±1.0°C temperature compensation.

Pioneering Science and Technology Office of Science U.S. Department of Energy 34 Fringe Fields at X=65 and 100 mm Fringe fields with new shims are close to earth field for X=100 mm. (Earth field contribution to trajectory shift has to be corrected.)

Pioneering Science and Technology Office of Science U.S. Department of Energy 35 Fine adjustment of effective magnetic field (Isaac’s 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  m/mm cant) 3. Set horizontal position of the undulator as a whole so the effective field is in the range ±2 Gauss (  B/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 ±1°C needed). Such option is available, if quadrupoles are separated from undulator sections.

Pioneering Science and Technology Office of Science U.S. Department of Energy 36 Magnetic needles for alignment Only one needle is required for alignment in the X direction One more needle has to be added at Y=0 for alignment in the Y direction

Pioneering Science and Technology Office of Science U.S. Department of Energy 37 Outline – Prototype Undulator Status Design Challenges Mechanical Design Features Performance Post-Prototype Design Improvements Canted Pole Measurements Plans Summary

Pioneering Science and Technology Office of Science U.S. Department of Energy 38 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

Pioneering Science and Technology Office of Science U.S. Department of Energy 39 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].

Pioneering Science and Technology Office of Science U.S. Department of Energy 40 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

Pioneering Science and Technology Office of Science U.S. Department of Energy 41 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.

Pioneering Science and Technology Office of Science U.S. Department of Energy 42 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 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