1. Option – Material Choices Frame Strong-backs Magnet Modules Definitions

2. Option – Material Choices Default choice for magnetic structure strong back is Al Consider steel, carbon fiber Default choice for magnet module keeper is Al Must be nonmagnetic Potential thermal distortion for material different than strong back Default choice for frame is structural steel No alternatives considered Slide 2Undulator Alternatives- 5m 6-15-11

3. Option – Material Choices Anecdotal information from Flash/XFEL: Similar designs; both use Al magnet module keepers Flash uses steel strong back XFEL uses Al strong back Non-repeatability of optical phase measurements for Flash undulators Not fully understood, but believed to be due to differential thermal expansion between keepers, strong back Apparently corrected with XFEL undulators Steel/Al for strong back primary study Also consider carbon fiber for strong back Slide 3Undulator Alternatives- 5m 6-15-11

4. Strong Back Material Comparison Aluminum (6061) Steel (A36) Size* (l x w x h)(m)3.4 x.095 x.513.4 x.095 x.36 Weight (kg)474967 Material Cost ($/Strong back)$3550$1950 Machining Cost ($/Strong back)$1792$3072 Total Cost ($/Strong back)$5342$5022 CTE (Coefficient of Thermal Expansion) 23.4x10 -6 / 0 C11.9x10 -6 / 0 C CTE for Carbon Fiber ~ 2x10 -6 / 0 C *Al, steel strong backs sized for ~10 m max. deflection (SXU)

5. Differential Thermal Expansion Simple model with solid Al magnet module, steel strong back Ignores NdFeB blocks, VP poles – similar to steel Max. vertical deflection = 20 m/ C Slide 5Undulator Alternatives- 5m 6-15-11

6. Carbon Fiber (CF) for Strong Backs Discussion with composite structures group Typical application: high stiffness/weight (or mass) We dont care so much about weight Could likely increase stiffness compared to Al, but not steel Typically expensive for single structure, for multiple structures may be comparable to steel, Al Unusual application, would require R&D to qualify CF not good choice for keeper structure, would use Al for critical surfaces Al would dominate CTE Left with differential thermal expansion ~5x worse for Al/CF than for Al/steel Slide 6Undulator Alternatives- 5m 6-15-11

7. Conclusion CF strong back No cost advantage R&D required Differential CTE likely a problem Steel strong back ~Cost neutral Relatively small differential CTE affect (for 0.1 C), but anecdotal evidence of problems from Flash More compact Al strong back Least risk Only reason to consider steel is to reduce size Slide 7Undulator Alternatives- 5m 6-15-11