The role of hot electrons on ultrahigh pressure generation relevant to shock ignition conditions

Abstract

On shock ignition (SI) scheme of inertial confinement fusion (ICF), a spherical shell target is compressed by relatively low intensity laser pulse irradiation, and hot spot is ignited by converging shock waves by high intensity laser pulse called “spike pulse”. The SI scheme is considered as a promising scheme to reduce the required drive laser energy for ignition. On the SI scheme, the strong shock by the spike pulse should be over 300 Mbar (=30 TPa). The key physics to produce such ultrahigh pressure is the contribution of hot electrons generated by parametric instabilities. The hot electron generation, transport, and their effects on shock wave parameters in various experimental conditions were explored. This paper focuses on experimental parameter of 0.527 μm (2ω) irradiation as spike pulse with/without pre-pulse irradiation conditions, and the experimental data was compared with one-dimensional hydrodynamic simulation. Experiments with pre-pulse irradiation that pre-compresses a target before the main pulse with producing more hot electrons generates a strong shock and hot electrons lead to an enhanced shock velocity. This fact indicates that the hot electron absorption per unit length in the target is increased leading to an enhanced shock strength.