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LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
1 Jeff Dooling
SLAC SLAC Redwood Room A/B, SLACRedwood Room A/B, SLAC
Thursday, June 19, 2008Thursday, June 19, 2008
BLM Dosimetry Simulations in theBLM Dosimetry Simulations in theLCLS Undulator Magnets using LCLS Undulator Magnets using
MARSMARS
Jeff DoolingArgonne National Laboratory
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
2 Jeff Dooling
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
3 Jeff Dooling
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
4 Jeff Dooling
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
5 Jeff Dooling
Correcting the geometryAl. 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
6 Jeff Dooling
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
7 Jeff Dooling
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 108 macroparticles
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
8 Jeff Dooling
First Undulator results—considerations, con’t
Twiss parameters,
n=10-6 m-rad = =(=26,690)
for the moment,
x≈y==n/=3.8x10-11m-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
9 Jeff Dooling
First Undulator results—geometryPCMuon (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
10 Jeff Dooling
Neutron fluence and electron spectral fluencemagnet 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
11 Jeff Dooling
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 3rd order)
Using average optical coupling and quantum efficiencies over the wavelength range of interest (200-600 nm)
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
12 Jeff Dooling
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
13 Jeff Dooling
Summary of 1st Radiator/Undulator data—Radiator signal; peak undulator neutron fluence is also shown
Bunch charge
(pC)
Electron Fluence
(104cm-2)
Npe
(106)
Qout
(nC)
Iout
(A)
Peak Neutron Fluence (104cm-2)
200 0.46 0.23 18.5 7.39 0.45
500 1.19 0.60 48.3 19.3 1.15
1000 2.40 1.21 97.0 38.8 2.30
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
14 Jeff Dooling
More first undulator results—electron spectra with and without W enhancer
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
15 Jeff Dooling
More first undulator results—electron spectra varying rad. height w/o W enhancer
BLM signal ~ IspeVrad
Ispe,rrVr,rad=0.75 IspeVrad
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
16 Jeff Dooling
Multi-undulator model
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
17 Jeff Dooling
Radiator/Undulator locations
1 7 13 19 25 31
e-beam & shower
location numbersrefer to und. magnetsand upstream BLMradiators
Ti strongback
Al support struct.
magnet
magnet/pole mixt.
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
18 Jeff Dooling
Electron fluence spectra every 6th undulator—without the W enhancer
First radiator
Radiators 7, 13, 19, 25, & 31
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
19 Jeff Dooling
Electron fluence spectra every 6th undulator—with the W enhancer
First radiator
Radiators 7, 13, 19, 25, & 31
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
20 Jeff Dooling
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
21 Jeff Dooling
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
(105cm-2)
0.191 0.887 1.315 1.700 1.782 2.186
FN
(104cm-2)
2.322 0.422 0.865 0.805 1.127 1.081
FN/FE 1.216 0.0476 0.0658 0.0474 0.0632 0.0495
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
22 Jeff Dooling
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
(105cm-2)
0.236 2.398 2.835 4.111 4.480 5.369
FN
(104cm-2)
2.226 0.263 0.868 0.681 0.819 0.837
FN/FE 0.943 0.0110 0.0306 0.0166 0.0183 0.0156
LCLS Undulator Magnet Irradiation Sensitivity Workshop Thursday June 19, 2008
23 Jeff Dooling
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
24 Jeff Dooling
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/uE-spectrum altered with enhancerEnhancer 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
25 Jeff Dooling
Acknowlegments
Thanks to Bingxin Yang of Argonne and Heinz-Dieter Nuhn and Alberto Fasso of SLAC for many helpful discussions.
