Study of ultra-intense laser produced plasmas via
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Authors
Chrisman, Brian R.
Issue Date
2009
Type
Dissertation
Language
Keywords
absorption , cone target , electron transport , fast ignition , laser plasma interactions , PIC simulation
Alternative Title
Abstract
Recent advances in the development of intense short pulse lasers have led to exciting progress
in high energy density physics (HEDP). As an example, a several µm thin foil that is irradiated by
a 100 TW, sub-picosecond laser pulse reaches keV (1 keV ∼ 11,000,000 C) temperatures at solid
density. The resultant electron distribution is temporarily far out of equilibrium, featuring two or
more widely distinct temperatures. In modeling such extreme plasmas, both kinetic and collisional
effects on the energy transport are essential. Of particular difficulty are the large density gradients
between the critical density (the density at which the laser is absorbed), and solid densities exceeding
several hundred times the critical density. For a 1 µm wavelength laser pulse, the critical density, nc,
is 1021 cm−3
. This means that a numerical model needs to describe the laser-plasma interaction in
the low density region, as well as fast particle transport in the extremely dense target region where
Coulomb collision processes are important for energy transfer.
In cone-guided fast ignition inertial confinement fusion experiments, fuel previously compressed
by an ablative implosion is ignited by the injection of an intense short laser pulse via a cone embedded
within the fuel target. The implosion precondition creates density scales which range over five
orders of magnitude from the cone interior to the highly compressed core. A critical issue for this
process is whether the hot electrons produced in the interaction are in an energy range conducive
to efficient heating of the core. In this work, Particle-in-Cell simulations evaluate the entire coneguided fast ignition experiment for the first time, including hot electron generation at the cone tip,
energy transport to the compressed fuel core, and subsequent collisional core heating. The laserplasma interaction within the cone target is particularly important, as temperatures of hot electrons
generated here are found to be lower than previously expected while overall absorption is influenced
by non-linear electrodynamic processes.
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In Copyright(All Rights Reserved)