Fast ignitor: Fluid dynamics of channel formation and laser beam propagation

Abstract

The concept of fast ignitor is intimately connected with the fundamental phenomenon of ultra-intense light beam propagation through dense matter in which kinetic effects combine with radiation pressure dominated hydrodynamics to form a complex scenario of extremely non-linear physics. In this paper, the fluid dynamic aspect of channel formation in a highly over-dense plasma is studied and possible attenuation mechanisms of the propagating pulse are evaluated in one dimension. Under the assumption that mass ablation reaches a quasistationary state, the radiation-assisted ablation pressure, the speed of the bow shock, and the density steepening around the critical point are determined self-consistently from the ID fluid conservation relations and the electromagnetic wave equation. Due to ponderomotive profile steepening, the ablation pressure is reduced by 40% in the subsonic region and is dominated by the radiation pressure in the supersonic domain. Channel lengths are calculated for various intensities and pellet compression ratios. Likewise, the nonlinear propagation of a superintense electromagnetic wave in an underdense plasma channel is investigated for the ID case with the help of a relativistic fluid model.