Characterization of hot electrons in experiments relevant to the Shock Ignition approach to Inertial Confinement Fusion

Shock Ignition (SI) is an alternative approach to direct-drive Inertial Confinement Fusion based on the separation of the compression and the ignition phases.  The high laser intensity required in the ignition phase exceeds the thresholds for the generation of laser-plasma instabilities (LPI), generating large amount of supra-thermal electrons. These electrons could preheat the hotspot, with detrimental effects for the SI scheme, or assist in generating a strong shock.

In this context, we present the results coming from an experiment conducted on the OMEGA-EP laser facility aiming at characterizing this hot electron source. In the experiment, an high intensity UV interaction beam (1-ns UV I ~10¹⁶ W/cm²) was focused on a multi-layer planar target (175 μm CH / 20 μm Cu, 500 μm diameter), generating a strong shock and copious amounts of hot electrons. The hot-electron source was characterized in terms of maxwellian temperature T_h and laser to hot-electron energy conversion efficiency η using different spectrometers, exploiting the radiation emitted by the passage of the electrons in the target.

The post-processing of the spectrometer data relies on using Monte Carlo codes in which the propagation of the electron beam in the target and the detector responses are simulated.