Dependence of Hot Electron Generation on Hydrogen Concentration of Target Materials for Shock Ignition Scheme of Direct-Drive Inertial Confinement Fusion

Shock ignition (SI) scheme is one of promising approaches for controlled nuclear fusion where a fuel capsule is imploded in two stages: compression stage and ignition stage, which requires more than 30 TPa of ultrahigh pressure creation by high intensity spike pulse irradiation in the ignition stage. In spike pulse (10¹⁶ W/cm²), hot electrons are produced by parametric instabilities and hot electron assisted laser ablation is considered. Although hot electrons should be avoided in terms of fuel preheating in compression stage, it is pointed out that hot electrons enhance ablation pressure in the SI scheme since compressed capsule in ignition stage already has high arial density, which indicates the control of hot electrons is crucial. We aim to control hot electron generation by target-based approach. Ablator materials of different H concentration: polyethylene (CH₂, 66 at%), polystyrene (CH, 50 at%), and diamond (C, 0 at%) were explored in the SI relevant conditions at GEKKO-XII laser facility, where a planer target can be irradiated by pseudo-single beam bundled 12 laser beams. In the presentation, we will show the experimental results for hot electron characterization with simulation calculations which explain hot electron generation increases with increasing H concentration.