Transcript Document

LSP modeling of the electron beam propagation in the nail/wire targets
Mingsheng Wei, Andrey Solodov, John Pasley, Farhat Beg and Richard Stephens
Center for Energy Research, University of California, San Diego
LLE, University of Rochester,
General Atomics, San Diego
Electron beam propagation and heating of the background plasmas in method 1
- Use LSP hybrid code to simulate large scale plasma that is comparable to the
real experiments.
- Study the electron beam transport in the nail/wire target
- Benchmark code against the experiments
Nail target, Cu2+ plasma, 20μm diameter wire
Wire target, Cu2+ plasma, 50 μm diameter wire
t=0.5ps (pulse center)
t=0.5ps (pulse center)
We aim to accurately model the nail/wire experiments
That means properly describing the experiment as well as properly simulating the physics
 Target geometry
 Laser pulse - including prepulse
 Properly generate current
 Analyze in terms of diagnostics
Preformed plasma produced by the laser prepulse has been modeled using the 2d rad hydro code h2d.
Density contour in low  region
high  region
Courtesy of
P. Patel at LLNL
Initial target
position at z=0
r =7μm
r =0
Two methods used for modeling the experiment with LSP code
r =25μm
Energetic electron beam production, propagation and heating of the background plasmas in method 2 (preliminary results)
 Method 1: Hot electron beam promoted from the background electrons
using the empirical scaling
pulse: Gaussian, 0.5 ps (FWHM)
energy: 81 J
spot size: 16.4 µm (FWHM)
intensity: 51019 W/cm2
r =17μm
r =0
r =10μm
kinetic electron density
r=0.9 µm
r=7.6 µm
r=25 µm
Background electron temperature
Hot electron current vs time
conversion efficiency: 30%
average energy: Th~2.23 MeV
angular spread: 34 (half-cone angle)
t = 0.5 ps
t = 1.0 psc
t = 1.4 ps
t = 0.5 ps
t = 1.0 ps
 Method 2: Hot electron beam produced from the laser plasma interaction
12 µm underdense plasma
kinetic electrons
300 µm
Ti wire Target:
- 12 µm kinetic electrons
(underdense to critical density)
- background solid density Ti(+15) with
Tinitial 100 eV, electrons as the fluid species
50 µm
 10% of laser energy is transferred to hot electrons which cause significant reduced heating
compared to that using the excitation model.
 MA current is carried by hot electrons.
 Hot electron density drops quickly (by 10 fold) in the first 20 µm.
 Strong azimuthal B field and radial E field are generated on the wire surface.
Laser beam launched
from the left boundary
- Focal spot size: r0=7.5 µm
- 65 J in the focal spot
- 0.5 ps (top hat profile)
- I~ 7.361019 W/cm2, a0=7.4
Grid szie:
- r: 0.312 -0.615 µm
- z: 0.182 - 1 µm
-Time step: 0.03um
B ~ 25 MG
Er ~ 2.5 MV/µm
Future work:
 Simulation for the longer wire case
 Including the self-consistent ionization model
 Analyze the simulation data in terms of diagnostics used in the experiments
t = 1.0 psc
This work is supported by the U.S. Department of Energy under Contract No. DE-FG03-00ER54606, No. DE-FC02-04ER54789, and No. DE-FG02-05ER54834
This work is also partially supported by the National Center for Supercomputing Applications under grant number PHY050034T and utilizes the computer facilities in SDSC.
t = 1.4 ps