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°