1. Angular distribution of fast electrons and
protons in short pulse laser target interaction
Hui Chen
Yuan Ping, Ronnie Shepherd, Jim Dunn- LLNL; Dustin Offermann, Anthony Link,
Linn Van Woerkom - OSU; James King, Farhat Beg - UCSD; Cliff Chen - MIT;
Lee Elberson, Windell Hill -U. Maryland
Modeling by Andreas Kemp and Scott C. Wilks LLNL
Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

2. Angular distribution of electrons and protons measurements are important for understanding the laser target interaction
Hot electron measurements often have been
at single position/angle relative to target
Proton measurements have concentrated
on the back of the target where they are most
energetic and beam-like
Highly non-uniform distributions of
hot electrons have been found by several groups
The group of Zhang et al. ( ) looked at hot
electrons at intensities up to mid-1018 W/cm2
Malka and Miquel
(1996) did first Thot at
three angles at upper -
1018 W/cm2
Chen et al. APS DPP 2006
Electrons, 2D PIC, Wilks
We will attempt to answer the following questions with detailed experiments:
What is the correlation between the electron dose and its distribution for all angles?
What is the correlation between the spatially resolved hot electrons and the protons?

3. The measurements were performed on the Callisto laser with peak intensity of 3x1018 to 6x1019W/cm2
Chamber center photo
Exp. setup
Lasers:
E= J, 130 fs, FWHM focus~5um
Diagnostics:
Proton ring with radiochromic film (RCF)
Two Proton spectrometers using image plates
Electron spectrometers using image plate(4 - 7)
Ultra-thin thermoluminescence dosimeters
TLDs ( )
Targets:
1 to 50 um thick foils of two sizes:
A) 2 x 10 mm2 flat foils of CH, Al, Cu, Ag
B) ~ 0.2 x0.2 mm2 foil reduced mass targets of Cu
Mounted flag-style on glass fiber
P-spec

4. Full angular coverage of TLDs was complemented by calibrated E-spectrometers at several positions
TLDs: electron dose for E>350 keV (red)
electron dose for E>1 MeV (blue)
Especs: spectra for MeV at many 
Laser
E > 1 MeV
E > 350 KeV
Dose
Abs Calibration
Angle
E-spec #2
TLD: ~6e-7 J for E>350 keV
E-spec: 2e-6 J for E>100 keV
Quantitatively consistent
diagnostics
Tanaka et al, 2004
Chen et al, 2007

5. Electron distributions and temperatures from two laser intensities for the same target condition
0.5 MeV
0.7 MeV
Target front
3x1018 W/cm2
3x1019 W/cm2
~Laser direction
0.5 MeV
0.6 MeV
Back normal
0.8 MeV

6. 2D PIC modeling shows hot electron behavior similar to that observed in the experiments
Electrons from back are hotter than
Those from front of target
Electrons are accelerated mostly
In the forward direction
Electrons are accelerated mostly
In the forward direction
Black:all particles gb
x (c/w0)
5e19 W/cm2
5e19 W/cm2
Forward direction
Forward direction
Laser
2D PSC modeling by Andreas Kemp
Under-dense
Over-dense
Electron temperatures are higher at the back of the target than at the front of the targets

7. The proton spatial distribution was recorded by the RCF ring (E>1
The proton spatial distribution was recorded by the RCF ring (E>1.3 MeV) and proton spectrometers ( MeV)
Proton dose
Target edge
Front normal
Film label
Target edge
Back Normal
Spectra from 2 proton spectrometers at front and back of target normal positions
Target back normal
Laser
Target
Target front normal
The Ring
Noise level

8. The proton distributions for large and small targets are dramatically different, so are the proton doses
Beam like protons from large foils
of metal and CH
10 um Ag, CH
2x10 mm2
5e19 W/cm2
Broader proton distributions
in reduced mass targets
10 um Cu
0.2 mm2
5e19 W/cm2
1e19 W/cm2
Electrons: 5e19 W/cm2
More than a factor of 2 higher conversion from laser to
protons are found in reduced mass target

9. The near isotropic proton acceleration in reduced mass targets can be explained by their unique E-fields
2D PSC modeling by Andreas Kemp
Reduced Mass Targets accelerate protons not only from front and back, but all sides of target, due to near equal electric field strengths everywhere around the target.

10. Conclusions
Measurements were performed on the Callisto laser with a peak
intensity of 3x1018 to 6x1019W/cm2 with full angular coverage using
Multiple charged particle detectors.
We found:
The electron angular distributions are highly anisotropic.
Electron temperatures in the forward directions are hotter than the backward direction.
The proton distributions for reduced mass targets tend to be more isotropic than distributions from large targets. Less difference was observed for hot electrons for these two target types.
The 2D collisional PIC simulations of the electric field for reduced mass targets agree with observations