Bremsstrahlung measurements of electron divergence
Cliff Chen
Special FSC Meeting on Electron Divergence in Fast IgnitionAugust 5, 2010
The angular distribution of Bremsstrahlung emission constrains the divergence angle and conversion efficiency
0 10 20 30 40 50 60 70 80 900.0E+00
5.0E-03
1.0E-02
1.5E-02
2.0E-02
2.5E-02
3.0E-02
Bremsstrahlung Response for 1.2MeV 1-Temp. Electron Source
EDA Response
Line Response
Narrow Response
PIC Response
Wide Response
Angle (degrees)
Ag Foil Target
EdN
/dO
meg
a (M
e V/S
R/ e
-)
The angular distribution of Bremsstrahlung may be useful for inferring the electron divergence angle.
0 10 20 30 40 50 60 70 80 900
0.5
1
1.5
2
2.5
3
3.5
20 deg HA75 deg HACEAexp(-(theta/50deg)^4)
Angle (degrees)
EdN
/dO
meg
a (M
eV/S
R/e-
)
Injected Electron Distribution 1.2 MeV 1-Temp
CEA0 deg20 deg HA
75 deg HAexp(-(theta/50deg)^4)
Diagnostic Setup
0°
28°66°
6°
35°
10 Al / 500 Ag / 1mm CH
Al & Ag:1x1 mmCH: 5x10 mm
0.7 ps, 7 μm FWHM, Ipeak≈1020 W/cm2
≈10 mJ prepulse
16°
3 rear surface spectrometers are simultaneously fit using Monte Carlo modeling of an electron beam
e- injected isotropically with max angle
Bremsstrahlung emission matrix calculated for each:-Spectrometer Location-Max Injection Angle
Central Angle can also be varied
• 2-T electron distributions are simultaneously fit to each spectrometer for each angular distribution
• Minimum reduced χ2 is calculated for each angle parameter
0 10 20 30 40 50 60 70 80 9005
101520253035
20100719s0620100720s0420100729s03
Half Angle-Isotropic Distribution
Min
imum
Fitti
ng P
aram
eter
(red
Chi
sq)
148 J
157 J
40 J
Electron Divergence in Planar Geometry
0 2 4 6 8 10 12 14 161
10
100
Dosimeter Layer
Sign
al (P
SL)
0°
28°66°
157 J
0 2 4 6 8 10 12 14 160.1
1
10
Dosimeter LayerSi
gnal
(PSL
)
40 J
Best Fit = 60±5°, ηLe-=30%
Fitting hν > 100 keV = 50±5°, ηLe-=34%
Best Fit = 60±5°, ηLe-=32%
Fitting hν > 100 keV = 50±5°, ηLe-=36%
0°28°
66°
