Study of ultra-intense laser produced plasmas via
AuthorChrisman, Brian R.
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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.