Physics Issues for Conventional Facilities

1. Physics Issues for Conventional Facilities Review and Update 10/12/04 J. Welch

2. Topics • Physics Sensitivities Review • Ground Motion and Magnet Support Studies • Vibration Studies • Undulator Hall Thermal Calculations

3. Sensitive CF Areas X most critical

4. Xray-Beam Phase Tolerance • Trajectory Straightness • 2 m rms tolerance for the electron beam 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 Strength 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.

5. Alignment Stability • Ultra-straight trajectory will be lost if • BPM’s move a few microns and feedback incorrectly corrects the beam • Quads move a few microns • 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) • unless the actual motion is known, there is no effective way to re-establish the undulator position except through conventional alignment. • BBA once a month is OK, once a day intolerable

6. Implications for Undulator Hall • Make foundation as stable as possible • Thermally stabilize the Undulator Hall • Heat fluxes must be reduced to a minimum to avoid thermal distortions • The tunnel air temperature must be regulated to within a ± 0.2 deg C band everywhere in the Undulator Hall.

7. Ground Motion Studies • Linac and PEP data Analyzed • Correlation with distance measured • Histograms of actual motion of adjacent points • Startup effect • Estimated UH floor motion revised • Short term motion is under analysis

8. 17 Year Linac Elevation Change • Measured motion of points along the linac every 12 m over a 17 year period. • Scale Is 1000X bigger than our sensitivity • Linac has 2 ft thick, heavily reinforced floor

9. Linac 17 year Motion • 17 year average rate of change of differences between adjacent points (12.3 m separation) is plotted • Tails are non-gaussian, but relatively small.

10. Startup Effect • PEP data • Much greater velocities occur in the first few years after construction • Motion continues at a signficant level indefinitely • Model of Seryi and Raubenheimer give about a factor of two between 17 year average rate and first three average rate.

11. Correlation with Distance • Relative motion correlates with distance between measurement points. • LCLS will have support points around 10 m apart, and quad separation of 4 m. • Stiffness of foundation may improve this correlation.

12. Predicted UH Slow Floor Motion • Estimate for typical motion during first three years. It is twice the 17 year average differential rate for the linac. • Doesn't include motions of supporting structures • Doesn't include daily or seasonal effects • Motion is cumulative. That is rms grows linearly with time.

13. Undulator Hall Profile Fill Area

14. Short term motions in Linac • Short term motions were measured on linac • 24 hour average rms ~ 7 microns • 1 hour average rm ~ 1.2 microns • Motions mostly due to atmospheric pressure and tides. • Measurements were over a 1000 m baseline • Need to extrapolate to 10 m, ATL? • Seasonal effects not included pressure From A. Seryi

15. Magnet Support Studies • Motion of the floor affect quadrupole motion differently depending the support scheme

16. Single Column Support

17. 3 Quads per Girder

18. Phase Error Correlations

19. Support Study Conclusions • Griders couple the motion of adjacent quadrupoles, thereby largely canceling the steering effects caused by the motion of the tunnel floor. • Analysis shows a five fold reduction in phase error is possible with girders compared with single column support.

20. Vibration • UH borehole vibration measurements at 20 ft depth • Ambient ~ 4 nm rms • Ave dumptruck ~ 18 nm rms • Ave dumptruck on gravel ~ 40 nm rms • Max dumptruck on gravel ~ 150 nm rms • Higher vibration levels near surface • "Static" deformation due to truck yet to be estimated. • We need vibrations to be below 1 m

21. Heat Transfer Problem • Basic problem is that it is hard to heat the hillside without introducing temperature gradients in the tunnel air • Temperature drops at boundary between tunnel wall and bulk tunnel air due to boundary layer. Amount of drop depends of heat transfer coefficient. • Estimates of hc based on • McAshen (laminar forced convection): 0.59 W/m2C • Kreith (free conv. enclosed box): 0.5 - 2.0 W/m2C • Mark's H'book (horz. Cylinder): 0.6 - 2.3 W/m2C • Lower estimate are for small ∆T (0.1˚C), higher hc result for larger ∆T, (5-10 ˚C)

22. ANSYS Calculation Wall Temperature After 6 months = 17.1 C (Tunnel air at 20.0C) h = 0.6 W/m2˚C (note the movie of the transient temmperature response on the next slide will not work on some computers)

23. Movie on Transient

24. Summary of Physic Issues • Ground Motion Studies • 0.5 m rms/day cumulative differential motion, plus some short period motion, expected for floor stability • Girder support, in principle, can reduce sensitivity to floor motion • Vibration Studies • Don't appear to be a significant problem in Undulator Hall • Undulator Hall Thermal Stability • Potential problem with cold tunnel walls. Analysis continues

25. Extra Slides

26. 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

27. 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

28. 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.

29. 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.

30. 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.

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

32. 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

33. 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

34. 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

35. 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

36. 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 expected to be not quite as good as 1/10 sigma

37. Vibration and Pointing Stability • Angular tolerance can be converted to a vibration amplitude for a specific frequency, for CF spec. • y=A cos(kx-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

38. 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)

39. 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

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

41. 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.