Influence of laser-induced Au-plasma plume collision on the efficiency of x-ray radiations and the energy-transport process relevant to ICF

Abstract

Experiments and simulations have been carried out to study the colliding process by two lasers irradiating a gold half-hohlraum. Via analyzing the evolutionary x-ray images, radiation fluxes and self-emission spectrum of tracers, influence on the x-ray conversion efficiency and the local plasma temperature $T_{e,i}$ from two gold-plasma plumes have been investigated deeply, which is similar as the configuration in Inertial Confinement Fusion (ICF). Experimental results confirm a region with high electron and ion temperatures $T_{e,i}$ are induced, satisfying the strong collision condition of $\lambda_{i} \lt \Delta{L}$ , where λ _i and $\Delta{L}$ are respectively the ion mean-free path and the gradient length of T _e . It leads to almost $30\%$ increasing of M-band component compared to that from a single laser-irradiation case. Meanwhile ion temperature in this region increases more rapidly than electrons, reaching about $T_i\approx(16\pm4)$ keV ( $T_e\approx(2\pm 0.2)$ keV). Thus, our studies provide the experimental evidence of quantitative x-ray enhancement and a non-equilibrium evolution simultaneously due to the plasma collision for the first time. Besides, two-dimensional simulation results reveal that this process can not be precisely described by the traditional shock-heating model by dissipating the shock energy only to ions. But by distributing the viscous heating between both electrons and ions as theoretically discussed by Miller (2020 Comput. Fluids 210 104672), numerical results can match experiments better. This discovery will be of great importance to improve the precision of prediction for ICF.

Keywords

• inertial confinement fusion
• plasma collision
• non-equilibrium
• shock-heating