1. Undulator Line Design Liz Moog, Advanced Photon Source April 24, 2002
Requirements for individual undulators
Radiation considerations
Undulator magnetic design and model calculations
Initial results from prototype
Controls
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

2. Cell structure of the LCLS undulator line
3420
187
421
UNDULATOR
11055 mm
Horizontal Steering Coil
Vertical Steering Coil
Beam Position Monitor
X-Ray Diagnostics
Quadrupoles
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

3. Requirements for individual undulator segments - 1
Trajectory straightness
Beam will be centered at the beam position monitors between undulators; trajectory must remain straight in undulators
Allowed x and y deviation is 2 µm (0.2% increase in gain length)
At GeV, this corresponds to a second integral of the field of 9600 G-cm2 (or, at 4.5 GeV, 3000 G-cm2)
Magnetic measurement reproducibility for second integral is now ~ 1000 G-cm2
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

4. Requirements for individual undulator segments - 2
Reduction in first-harmonic radiation at zero angle
Allowed reduction is 4%.
Corresponds to 1.1% increase in gain length
In practice, the reduction can be calculated by comparing to the best of the undulators
Phase deviation
Allowed deviation from the design value (2π * integer) is 10°
Corresponds to 1.7% increase in gain length
Measurement reproducibility is now 0.5°
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

5. Requirements for individual undulator segments - 3
Vertical alignment
Undulator midplane must be determined (and aligned) to 50 microns vertically
50 microns displacement gives ~ 10° in phase slippage
Combined effect of these errors is 3% growth in power gain length
Requirements have all been met in the APS FEL
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

6. Requirements for individual undulator segments - 4
Uniformity of magnetic field strength
Error in magnetic field strength in an undulator by ∆B/B = 1.5 x 10-4 gives a phase error of 10°
Simulations using the code RON agree, finding significant change in gain when variation reached 1.3 x 10-4
This is error in B of 1.7 G (or gap error of 1.2 µm)
May impose requirements on temperature uniformity along the undulator line
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

7. Undulator Ends
Undulator ends will be tuned to keep trajectory straight
Sequence of end pole field strengths near 1/4, -3/4, 1, -1
No offset and no angle kick
Ends will be tuned for proper phase
For APS undulators, phase can be adjusted by ±38° by tuning
Alignment tolerance for installation is 1 mm
Remote adjustment of phase will be possible
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

8. Break lengths
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

9. Radiation considerations - What damages magnets?
Bending magnet irradiation (~40 keV photons), up to 280 Mrad: no effect*
60Co (1.17 MeV photons), up to 700 Mrad: no effect*
17 MeV electrons: at 260 Mrad, 9% remanence loss†
Above a few MeV, the shower produced includes both electrons and photons, independent of whether the initial particle was electron or photon
* Alderman, et al., ANL-APS LS-290.
† Okuda, et al., NIM B 94 (1994) 227.
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

10. Radiation considerations - What damages magnets?
Radiation-induced demagnetization has been seen at both ESRF (6 GeV) and APS (7 GeV), so the GeV LCLS should be quite capable of damaging magnets
There is no space to pile Pb shielding upstream of each undulator.
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

11. How can likelihood of radiation damage be reduced?
Controllable factors :
Magnet grade - i.e., intrinsic coercivity iHc
Lower coercivity of the magnet correlates with greater sensitivity to radiation damage
(Van Vaerenbergh et al., RADECS 99 proceedings;
Ikeda and Okuda, NIM A407 (1998) 439)
Magnetic environment - i.e. local demagnetizing field in the magnet block
Correlation found between stronger demagnetizing field during irradiation and greater likelihood of demagnetizing
(Brown and Cost, J. Appl.Phys 63 (1988) 3537, and IEEE Trans Magn. 25
(1989) 3117)
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

12. Magnet grades Data sheet from Shin-Etsu
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

13. LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

14. Calculated characteristics of magnetic model
Period is 30 mm
At 6 mm gap,
Bpeak=13897 G
Beff = G (13250 G desired)
Keff = (3.71 desired)
force per pole = 258 N (or 58 lbs.)
transverse position where ∆B/B=1.3x10-4 is at 2.9 mm
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

15. LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

16. LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

17. LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

18. LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

19. LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

20. LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

21. Initial results from prototype undulator
Actual field strength is stronger than predicted by model calculation
Keff = instead of 3.78
Gap of undulator will be adjusted (by about 0.3 mm) to compensate
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

22. Controls - 1
Controls will be based on EPICS and will build on existing controls at APS
Where possible, integrate with commercial off-the-shelf components
Support multiple devices on single fieldbus network
Custom design when needed
APS-designed valve controller
Vacuum interlocks
Low frequency data collection for vacuum controls
Short-haul wireless technology (e.g. Bluetooth) may integrate well
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS

23. Controls - 2
High motor count dictates dense control scheme; encoders assumed
Diagnostics
High speed cameras and frame grabbers (>120 Hz) should be available in the near-term
PC based analysis is becoming industry norm
Allows rapid analysis and easy upgrades
Magnet power supplies controlled via fieldbus
Phase correctors use PZT stages controlled with commercial hardware - few stages per controller
Investigate custom hardware?
LCLS DOE Review, April 24, 2002
Liz Moog, ANL / APS