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Physics Requirements for Conventional Facilities

Physics Requirements for Conventional Facilities. Thermal, Settlement, and Vibration Issues J. Welch Lehman Review, August 2004. Sensitive CF Areas. … Start with Undulator Hall (UH). Physics Sensitivities for UH.

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Physics Requirements for Conventional Facilities

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  1. Physics Requirements for Conventional Facilities Thermal, Settlement, and Vibration Issues J. Welch Lehman Review, August 2004

  2. Sensitive CF Areas … Start with Undulator Hall (UH)

  3. Physics Sensitivities for UH • FEL saturation length (86 m) increases by one gain length (4.7 m), for the 1.5 Angstrom case if there is: • 18 degree rms beam/radiation phase error • 1 rms beam size ( ~ 30 mm) beam/radiation overlap error. • Xray beam will move 1/10 sigma if • electron trajectory angular change of ~ 1/10 rad

  4. FEL Mechanism Micro-bunching Narrow Radiation Cone ~1 mr, (1/g ~ 35 mrad) • 2p radiation phase advance per undulator period Relationship of Xray phase to wiggle phase is critical; 3729 periods

  5. Phase Sensitivity to Orbit Errors Path Length Error Phase Error from H-D Nuhn LCLS: A < 3.2 mm LEUTL: A < 100 mm VISA: A < 50 mm

  6. Implications of Phase Tolerance • Trajectory Stability • 2 m rms tolerance for the electron beam trajectory deviation from ideal trajectory, averaged over 4.9 m (power gain length) • Maintaining an ultra-straight trajectory puts demanding differential settlement and thermal requirements on the Undulator Hall • Undulator magnet uniformity • ∆K/K <= 1.5 x 10-4 for 10 degrees error per undulator segment • Undulator alignment error limited to 70/200 micron vertical/horz. • Temperature coefficient of remanence of NdFeB is 0.1%/C, which, because of partial gap compensation via Ti/Al assembly, leads to a magnet temperature tolerance of ± 0.3 C.

  7. Obtaining an Ultra-Straight Beam • BBA is the fundamental tool to obtain and recover an ultra-straight trajectory over the long term. • Corrects for • BPM mechanical and electrical offsets • Field errors, (built-in) and stray fields • Field errors due to alignment error • Input trajectory error • Does not correct undulator placement errors • Procedure • Take orbits with three or more different beam energies, calculate corrections, move quadrupoles to get dispersion free orbit • Disruptive to operation

  8. Maintaining Alignment • Ultra-straight trajectory will be lost if • BPM’s move and feedback incorrectly corrects the beam • Quads move • Stray fields change • Launch trajectory drifts • Phase accuracy will also be lost if • undulator segments move ~ 10 m, (50 m assuming zero fiducialization and initial alignment error) • note that unless the actual motion is known, there is no effective way to re-establish the undulator position except through magnetic measurements. • BBA once a month OK, once a day intolerable

  9. Motion Due to Temperature Change • Dilatation T ~ 2 m / 1.4 m x 10 x 10-6 = 0.14 deg C 1.4 m (for a nominal 10 ppm/deg C) Low CTE materials desirable Enviroment must be constant temperature to ~ 0.1 - 0.2 deg C

  10. Motion Due to Heat Flux or temperature gradients d Note that 3 W/m2 can be generated by ~1 degree C temperature difference between the ceiling and floor via radiative heat transfer e.g. 3 W/m2 -> 2 micron warp for an undulator strongback, or ∆T ≈ 0.05 deg C across strongback Minimize heat fluxes, isothermalize where possible

  11. Undulator Hall Thermal Tolerance Summary • Dilatation 0.1 - 0.2 deg C • K sensitivity 0.3 deg C • Thermal Flux 3 W/m2 • Spec on air temperature • +- 0.2 deg C • Thermal flux 50 W/m of tunnel • Isothermal, all surfaces within 1 deg C.

  12. Title I Undulator Hall HVAC Alcoves with AHU’s Make up air Cross flow to ducts AHU in alcoves 9X Return Air Tempered water, slightly warmer and cooler than the tunnel air, is supplied to each of the AHU’s Variable flow local recirculating loop in AHU

  13. Motion of the Foundation 1 mm/year = 3 m/day

  14. Settlement Prior to Loma Prieta Quake • 400 mils = 10 mm

  15. Implications for Undulator Hall • Expect differential settlement of 1 - 3 m / day, in some locations. • Make foundation as stable as possible • geotechnical, foundation design, uniformity of tunnel construction and surrounding geologic formation, avoidfill areas

  16. Title I Undulator Hall Foundation • Completely underground • Impervious membrane blocks groundwater • Located above water table (at this time anyway) • Low shrink concrete, isolated foundation • “Monolithic” High Moment of Inertia, T shaped foundation Pea Gravel support Slip planes

  17. Magnetic Measurement Facility • Air Temperature • ± 0.1 deg C band everywhere in the measurement area. • 20.0 deg C year round temperature • Vibration • Hall probe motion is translated into field error in an undulator field such 0.5 m motion causes 1 x10-4 error. • Measurements show vibrations below 100 nm.

  18. Sector 20 • RF electronics • Timing signals sensitive to temperature • Special enclosure for RF hut • Laser optics • Sensitive to temperature, humidity and dust, vibration • Class 100,000 equivalent, humidity control, vibration isolated foundation (separated from klystron gallery), fix bumps in road nearby.

  19. Near Hall • Hutches, to house a variety of experiments, need • Thermal, humidity, and dust control • Class 10,000 equivalent • Adjacent to Near Hall are Xray beam deflectors which have significant vibration sensitivities.

  20. Xray Beam Pointing Sensitivity ’FEL ~ 1 rad Near Hall FEL ~ 400 m Far Hall Undulator 250 m ~ 320 m ~ 400 m

  21. Pointing Stability Tolerance • 0.1  spot stability in Far Hall (conservative) implies 0.1 rad pointing stability for deflecting crystals and electron beam • Feedback on beam orbit or splitter crystal can stabilize spot on slow time scale. • Still have to face significant vibration tolerances on deflecting crystals • Corrector magnets in BTH must be stable to better than 1/10 sigma deflection net. • Electron beam stability is not expected to be not quite as good as 1/10 sigma

  22. Vibration and Pointing Stability • Angular tolerance can be converted to a vibration amplitude for a specific frequency, for CF spec. • y=A coskx-t where y is the height of the ground, dy/dx is the slope. • We want average rms(dy/dx) ≤ 0.1 rad •  A ≤  0.1 rad/2.  is the wavelength of the ground wave • Typical worst case is around 10 Hz and speed of ground wave is around 1000 m/s. •  A ≤ 10-5/ 2 ~ 10-6 m, which is quite reasonable since typical A~100 nm or less • High Q support structures could cause a problem

  23. Conclusion • Reliable production of ultrahigh brightness, FEL x-rays requires • Exceptional control of the thermal environment in the Undulator Hall and MMF • Excellent long term mechanical stability of the Undulator Hall foundation • Care in preventing undesirable vibration near sensitive equipment at several locations • Requirements are understood, what remains is to obtain and implement cost effective solutions.

  24. Extra Slides

  25. Material Properties ∆T W/m2

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