Simulations of High-Gain Shock-Ignited Inertial-Confinement-Fusion Implosions Using Less Than 1 MJ of Direct KrF Laser Energy

摘要

In this paper, we report on recent numerical simulations of inertial- confinement-fusion (ICF) implosions using the FAST radiation hydro-code at the U.S. Naval Research Laboratory. Our study focuses on three classes of shock- ignited target designs utilizing less than 1 MJ of direct KrF laser energy, which was 'zoomed' to maximize the coupling efficiency. In the shock-ignition approach, a moderate-intensity, compressive laser pulse is followed by a short- duration high-intensity spike that launches a spherically-convergent shock wave to ignite a thick shell of compressed fuel. Such an arrangement appears to offer several significant advantages, including a low ignition threshold, high gain, and less susceptibility to the deleterious effects of hydrodynamic and laser-plasma instabilities. According to one-dimensional simulations, fusion gains over 200 can be achieved with shock-ignited targets using less than 750 kJ of laser energy. This represents a significant improvement in performance over conventional centrally-ignited designs. To examine the stability of these targets, several two-dimensional simulations were also performed that incorporated realistic perturbation sources such as laser imprinting and roughness spectra for inner/outer pellet surfaces. Although the simulations indicate that appreciable low-mode distortion of the fuel shell can occur at late time as a result of these perturbations, high gains are still achieved in many cases owing to the low in-flight aspect ratios of shock-ignited targets. We should remark, though, that the high convergence ratios of these same designs suggest that other sources of low-mode asymmetries, which were not considered in this study (e.g., beam misalignment and energy-balance errors), may be important in determining overall pellet stability and performance.