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Option – Material Choices. Definitions. Magnet Modules. Frame. Strong-backs. 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
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Option – Material Choices Definitions Magnet Modules Frame Strong-backs
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 Undulator Alternatives- 5m 6-15-11
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 Undulator Alternatives- 5m 6-15-11
Strong Back Material Comparison CTE for Carbon Fiber ~ 2x10-6/0C *Al, steel strong backs sized for ~10m max. deflection (SXU)
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 Undulator Alternatives- 5m 6-15-11
Carbon Fiber (CF) for Strong Backs • Discussion with composite structures group • Typical application: high stiffness/weight (or mass) • We don’t 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 Undulator Alternatives- 5m 6-15-11
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 0.1C), but anecdotal evidence of problems from Flash • More compact • Al strong back • Least risk • Only reason to consider steel is to reduce size Undulator Alternatives- 5m 6-15-11