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LSP Calculations of ConeWire Experiments

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Title: LSP Calculations of ConeWire Experiments


1
LSP Calculations of Cone-Wire Experiments
  • Presented to
  • 8th International Workshop on
  • Fast Ignition of Fusion Targets
  • Tarragona, Spain
  • R. P. J. Town
  • AX-Division
  • Lawrence Livermore National Laboratory
  • June 30, 2005

2
Collaborators
  • L. A. Cottrill, M. H. Key, W. L. Kruer, A. B.
    Langdon, B. F. Lasinski, B. C. McCandless, H. S.
    Park, B. A. Remington, R. A. Snavely, C.
    H. Still, M. Tabak, S. C. Wilks, LLNL, Livermore,
    CA, USA.
  • J. F. Myatt, LLE, Rochester, NY, USA.
  • D. R. Welch, MRC, Albuquerque, NM, USA.

3
We have performed LSP calculations of recent RAL
experiments
Summary
  • Experiments have been performed at RAL using
    various targets that are important for a range of
    programs
  • Ka radiography
  • Isochoric heating
  • Electron transport for fast ignition and
  • Neutron star atmosphere.
  • To more directly compare to these experiments we
    have modified LSP to create photons in a
    non-interfering way.
  • We have performed LSP simulations of small planar
    and cone-wire targets and calculated the Ka
    yields.

4
We have performed LSP simulations of two types of
low-mass targets
  • 1D Flag targets
  • 2D Cone-wire targets

5
LSP1 can model larger, more dense plasmas for
longer simulation times than explicit PIC codes
  • LSP uses
  • a direct implicit energy-conserving
    electromagnetic algorithm
  • hybrid fluid-kinetic descriptions for electrons
    with dynamic reallocation and
  • inter-and intra-species collisions based on
    Spitzer collision frequencies.
  • The simulations reported here used
  • 2-D cylindrical geometry
  • a fixed ionization state throughout the
    simulation
  • an ideal gas EOS and
  • a hot electron beam created by promotion from the
    background plasma.
  • To generate photons a medium must be inserted
    into the plasma. The medium uses the Monte-Carlo
    ITS2 kernel. This model was modified so that the
    only effect of the medium was to generate photons.

1D. R. Welch, et al, Nucl. Inst. Meth. Phys. Res.
A 242, 134 (2001).
2J. A. Halbleib, et al, IEEE Trans. Nucl. Sci.
NS-39, 1025 (1992).
6
Currently, we use scaling laws to establish the
hot electron parameters from the laser intensity
  • Conversion Efficiency
  • ? 0.000175 I(W/cm2)0.2661
  • Hot Electron Energy
  • Pondermotive scaling
  • Thot(MeV) (Il2/(1019W/cm2mm2))1/2
  • Beg scaling
  • Thot(MeV) 0.1(Il2/(1017W/cm2mm2))1/3
  • We have also taken electrons from our explicit
    PIC code, Z3, and used them as the source in LSP.

7
These scaling laws were applied to the RAL
Petawatt laser pulse
  • Expect 80J of electrons injected (30 conversion
    efficiency)
  • Translates into 2.8x1014 electrons with an
    average energy of 1.7 MeV
  • The peak beam energy was 6 MeV

Peak of laser pulse
8
The hot electrons fill the planar target during
the laser pulse and are confined by the large
surface electric fields
0.25 ps
0.5 ps
9
By 1 ps, the hot electrons have flooded the
target and are constrained by the electric field
10
Using a non-interfering medium model we can
record the birth position of the photons
  • Energy into K-shell photons 2.7 kJ/g of Cu
    fluor.
  • K-shell conversion efficiency from electrons
    0.03

Calculated fwhm 18 mm
Ka
Experimental data
Kb
Bremsstrahlung
11
50mm radius target simulations confirm the effect
of refluxing
  • Energy into K-shell photons 54 kJ/g of Cu fluor
  • K-shell conversion efficiency from electrons
    0.04

R50mm 20mm spot size
R200mm 18mm spot size
The smaller target is significantly brighter
12
However, these small targets lead to high
background electron temperatures
  • The simulation used ideal gas EOS and a fixed
    ionization state.
  • We are currently adding QEOS tables to LSP.

Fluid electrons converted to particles
These high temperatures will cause line shifts
13
A non-LTE atomic physics model has recently been
added to LSP to account for thermal shifts
  • Time and space integrated spectra have been
    obtained that clearly show shifts in the Ka lines

14
LSP simulations have also been performed of the
2-D cone-wire targets
  • The bulk of the hot electron travel inside the
    wire, but some ride along the sheath at the
    wires edge.
  • The return current heats the background plasma
    electrons to similar temperatures to the planar
    targets.

Time 1.0ps
Time 0.3ps
15
Reduced filamentation was observed when a
transverse beam temperature was added
Time 0.3 ps
16
K-shell photons are produced along the length of
the wire
  • Energy into K-shell photons 26 kJ/g of Cu fluor.
  • K-shell conversion efficiency from electrons
    0.03

17
We have performed LSP calculations of recent RAL
experiments
Summary
  • Experiments have been performed at RAL using
    various targets that are important for a range of
    programs
  • Ka radiography
  • Isochoric heating
  • Electron transport for fast ignition and
  • Neutron star atmosphere.
  • To more directly compare to these experiments we
    have modified LSP to create photons in a
    non-interfering way.
  • We have performed LSP simulations of small planar
    and cone-wire targets and calculated the Ka
    yields.
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