Energy coupling in intense laser solid interactions: Material properties of gold

Abstract

In the double-cone ignition inertial confinement fusion scheme, a high density deuterium–tritium (DT) fuel is rapidly heated with high-flux fast electrons, which are generated by short and intense laser pulses. A gold cone target is usually used to shorten the distance between the critical surface and the compressed high density DT core. The material properties of the solid gold may affect the generation and transport of fast electrons significantly, among which the effects of ionization and collision are the main concerns. In this work, the effects of ionization, collision, and blow-off plasma on the laser energy absorption rate are investigated using the LAPINS code: A three-stage model is adopted to explain the mechanism of fast electron generation and the change in the laser energy absorption rate. With the increase in the charge state of Au ions, the laser–plasma interaction transfers to the later stage, resulting in a decrease in the laser energy absorption rate. Collision has both beneficial and harmful effects. On the one hand, collision provides a thermal pressure, which makes it easier for electrons to escape into the potential well in front of the target and be accelerated in the second stage. On the other hand, collision increases stopping power and suppress electron recirculation within the target in the third stage. The vacuum sheath field behind the target enhances the electron circulation inside the target and, thus, improves the laser energy absorption; however, this effect will be suppressed when the blow-off plasma density behind the target increases or collision is considered.