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W. J. Garbett

Publications and source records attributed to W. J. Garbett.

2 recordsLinked to original sources

Design of experiments characterising heat conduction in magnetised, weakly collisional plasma

Heat conduction in weakly collisional, magnetised plasma is challenging to model accurately due to multifaceted physics governing heat-carrying electrons, including microinstabilities that scatter electrons and modify heat transport. Capturing these effects requires multidimensional kinetic theory simulations, which are computationally expensive. Experimental constraints overcome this issue, resulting in improved understanding of thermal transport in systems such as the intra-cluster medium of galaxy clusters, and the hot-spot in inertial confinement fusion. In this paper, we present a new experimental platform that produces a weakly collisional high-\b{eta} plasma expected to be susceptible to the whistler heat-flux instability. This platform, to be fielded on the Orion laser, enables characterisation of whistler-regulated thermal conductivity. The platform design is assessed using radiation-magnetohydrodynamics simulations with the code FLASH. Simulations using three thermal conduction models predict conductivity suppression by over an order of magnitude relative to the Spitzer value at whistler saturation, demonstrating the efficacy of the platform.

physics.plasm-ph

Comparison between illumination model and hydrodynamic simulation for a Direct Drive laser irradiated target

A spherical target irradiated by laser beams located at 49o and 131o with respect to the polar axis has been considered. The illumination model has been used to evaluate the irradiation non-uniformity assuming circular and elliptical super-gaussian laser intensity profiles and the irradiation scheme has been optimized by means of the Polar Direct Drive technique. A parametric study has been performed providing the irradiation non-uniformity as a function of the Polar Direct Drive displacement and of the laser intensity profile parameters. Moreover, two-dimensional axis-symmetric hydrodynamic simulations have been performed for a plastic sphere irradiated by laser beams characterized by a constant flat temporal power pulse. In these simulations the front of the inward shock wave has been tracked providing the time-evolution of any non-uniformity. The results provided by the two methods - illumination model and hydrodynamic data - have been compared and it is found that the illumination model reproduces the main behaviour exhibited by the hydrodynamic data. The two models provide compatible values for the optimum Polar Direct Drive parameter and similar optimal super-gaussian profiles.

physics.plasm-ph