Physics Requirements for Conventional Facilities

1. Physics Requirements for Conventional Facilities Thermal, Settlement, and Vibration Issues J. Welch

2. General Background • What are Physics Requirements for CF? • Needed to accommodate technical systems • Distinguished from programming and site requirements • Used by system managers as input for further design • Where do they come from? • GRD, System physicists, system managers • Types of Requirements • Environmental, Layout, Space, Utility and Radiation • Critical Issues are Thermal, Settlement, and Vibration

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

4. 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 • ~ 1/10 rad change in angular alignment of various Xray deflecting crystals • electron trajectory angular change of ~ 1/10 rad

5. FEL Mechanism Micro-bunching Narrow Radiation Cone ~1 mr, (1/g ~ 35 mrad) • 2p radiation phase advance per undulator period Exponential Gain

6. 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

7. LCLS Phase Tolerance • Trajectory Straightness • 2 m rms tolerance for the electron trajectory deviation from an absolutely straight line, averaged over 4.7 m • 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 50/300 micron vertical/horz. • Temperature coefficient of remanence of NdFeB is 0.1%/C, which, because of partial compensation via Ti/Al assembly, leads to a magnet temperature tolerance of ± 0.2 C.

8. 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

9. 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

10. Motion Due to Temperature Change • Dilitation CTE ppm/deg C 1.4 m T ~ 2 m / 1.4 m x 10 x 10-6 = 0.1 deg C (for a nominal 10 ppm/deg C)

11. Motion Due to Heat Flux or temperature gradients d L = 3 m, titanium strongback 3 W/m2 -> 2 micron warp for an undulator segment ∆T ≈ 0.05 deg C across strongback Note that 3 W/m2 can be generated by ~1 degree C temperature difference between the ceiling and floor via radiative heat transfer

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

13. 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 • Thermally stabilize the Undulator Hall • reduce heat fluxes to a minimum • HVAC designed to precisely regulate temperature to within a ± 0.2 deg C band everywhere in the Undulator Hall

14. Title I Undulator Hall Foundation • Completely underground • Imprevious 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

15. Title I Undulator Hall HVAC Cross flow to ducts AHU in alcoves 9X

16. Magnetic Measurement Facility • Air Temperature • ± 0.1 deg C band everywhere in the measurement area. • 23.50 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.

17. 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.

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

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

20. 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. Typical SLAC beam is stable to better than 1/10  with feedback. • 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

21. 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

22. 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.