LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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?

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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?

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

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

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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 7 First Undulator results—considerations PCMuon just upstream 1-  m equivalent Al foil target at OTR33, 85 m upstream 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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 8 First Undulator results—considerations, con’t Twiss parameters,  n =10 -6 m-rad =  =  (  =26,690) for the moment,  x  y =  =  n /  =3.8x 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?

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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 ( nm)

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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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 )

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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 16 Multi-undulator model

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

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

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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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.

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 21 Comparison of radiator electron fluence with magnet peak neutron fluence without enhancer Rad. Pos. z (cm) “1” “7” “13” “19” “25” “31” FE (10 5 cm -2 ) FN (10 4 cm -2 ) FN/FE

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 22 Comparison of electron radiator fluence and peak neutron magnet fluence with W enhancer Rad. Pos. Z (cm) “1” “7” “13” “19” “25” “31” FE (10 5 cm -2 ) FN (10 4 cm -2 ) FN/FE

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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

LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008 Jeff Dooling 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)

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