1. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 1 SLAC Redwood Room A/B, SLAC Thursday, June 19, 2008 BLM Dosimetry Simulations in the LCLS Undulator Magnets using MARS Jeff Dooling Argonne National Laboratory

2. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 2 What damages undulator magnet material (NdFeB)? Neutrons Hadrons Heat —electrons and photons by themselves do not appear to lead to damage except in very high dose —can electrons be used as a proxy to estimate damage from the other sources?

3. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 3 BLM Dosimetry Calibrate—compare radiator electron fluence (Cerenkov signal) with neutron fluence (magnet damage) in the LCLS undulators using MARS Examine the calibration with differing loss scenarios; e.g., US foil strike, halo scraping in the FEL, beam misalignment or offsets. Does the calibration ratio change?

4. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 4 First, get the geometry right! Below is an earlier model showing a slice through the fused silica radiator should be opened

5. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 5 Correcting the geometry Al. radiator housing ap. specified with negative length x-y sect. y-z view length ignored

6. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 6 Corrected LCLS undulator geometry in MARS aperture specified correctly x-y sect. y-z view

7. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 7 First Undulator results—considerations PCMuon just upstream 1-  m equivalent Al foil target at OTR33, 85 m upstream 13.64 GeV electrons,  =26,690 Opening angle of shower  ~1/  =37.46  rad Bremsstrahlung height < 85 m(37.46x10 -6 ) ~3.2 mm Simulations conducted with 10 8 macroparticles

8. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 8 First Undulator results—considerations, con’t Twiss parameters,  n =10 -6 m-rad =  =  (  =26,690) for the moment,  x  y =  =  n /  =3.8x10 -11 m-rad From MAD model (LCLS04Nov07),  x,min =27 m/rad,  y,min =23 m/rad x’ max =(  x /  x ) 1/2 =1.2  rad, y’ max =(  y /  y ) 1/2 =1.3  rad x’ max,y’ max <<1/ , Will quads focus shower?

9. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 9 First Undulator results—geometry PCMuon (Fe) just upstream Location of XYZ Histogram regions in the pole/magnet material Quad ap. has been corrected and is reflected in present data

10. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 10 Neutron fluence and electron spectral fluence magnet neutron fluence distribution (top + bottom, so should divide by 2) radiator electron spectral fluence Magnet volume where “peak” neutron flux is evaluated

11. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 11 Radiator signal from Cerenkov Using Frank-Tamm formula Assuming ultra-relativistic form which varies by less than 4 percent at 2 MeV (lower limit) Fitting ln (SPE) vs. ln (E) simulation data with polynomial (typically 3 rd order) Using average optical coupling and quantum efficiencies over the wavelength range of interest (200-600 nm)

12. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 12 Radiator electron spectral fluence —first radiator 0.2, 0.5, and 1.0 nC on foil

13. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 13 Summary of 1 st Radiator/Undulator data—Radiator signal; peak undulator neutron fluence is also shown Bunch charge (pC) Electron Fluence (10 4 cm -2 ) N pe ( 10 6 ) Q out (nC) I out (A) Peak Neutron Fluence (10 4 cm -2 ) 2000.460.2318.57.390.45 5001.190.6048.319.31.15 10002.401.2197.038.82.30

14. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 14 More first undulator results —electron spectra with and without W enhancer

15. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 15 More first undulator results —electron spectra varying rad. height w/o W enhancer BLM signal ~ I spe V rad I spe,rr V r,rad =0.75 I spe V rad

16. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 16 Multi-undulator model

17. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 17 Radiator/Undulator locations 1 7 13 19 25 31 e-beam & shower location numbers refer to und. magnets and upstream BLM radiators Ti strongback Al support struct. magnet magnet/pole mixt.

18. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 18 Electron fluence spectra every 6 th undulator— without the W enhancer First radiator Radiators 7, 13, 19, 25, & 31

19. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 19 Electron fluence spectra every 6 th undulator— with the W enhancer First radiator Radiators 7, 13, 19, 25, & 31

20. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 20 Comparison in the DS radiators—with and without the W enhancer Radiators 7, 13, 19, 25, & 31 w/o enhancer Radiators 7, 13, 19, 25, & 31 w/ enh.

21. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 21 Comparison of radiator electron fluence with magnet peak neutron fluence without enhancer Rad. Pos. z (cm) “1” 13.24 “7” 2420.84 “13” 4828.44 “19” 7236.04 “25” 9643.64 “31” 12051.24 FE (10 5 cm -2 ) 0.1910.8871.3151.7001.7822.186 FN (10 4 cm -2 ) 2.3220.4220.8650.8051.1271.081 FN/FE1.2160.04760.06580.04740.06320.0495

22. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 22 Comparison of electron radiator fluence and peak neutron magnet fluence with W enhancer Rad. Pos. Z (cm) “1” 13.24 “7” 2420.84 “13” 4828.44 “19” 7236.04 “25” 9643.64 “31” 12051.24 FE (10 5 cm -2 ) 0.2362.3982.8354.1114.4805.369 FN (10 4 cm -2 ) 2.2260.2630.8680.6810.8190.837 FN/FE0.9430.01100.03060.01660.01830.0156

23. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 23 Work to do Add quadrupoles—presently coded into MARS; needs to be tested and debugged Add proper input distribution to electron beam (e.g., KV, Gaussian, other) Add halo distribution (second distribution) Look at beam offsets with distributions and halos

24. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 24 Summary Calibration of FN/FE changes substantially after the first radiator/undulator (highest neutron fluence here with foil shower—PCMuon?) Calibration ratio more stable for DS r/u E-spectrum altered with enhancer Enhancer modifies the environment around the radiator and to a lesser extent the US, center magnet section (reduces neutrons)

25. LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling jcdooling@anl.gov 25 Acknowlegments Thanks to Bingxin Yang of Argonne and Heinz-Dieter Nuhn and Alberto Fasso of SLAC for many helpful discussions.