Hard x-ray detectors for OMEGA and NIF

Laser–plasma instabilities that produce an unacceptably high level of hot electrons are potentially dangerous for both direct-drive and indirect-drive inertial confinement laser fusion. The hot electrons preheat the fuel and prevent compression of the capsule to the requisite conditions for ignition. Fast electron generation and preheat can be inferred from the hard x-ray radiation generated by the interaction of the hot electrons with the target. On the University of Rochester’s OMEGA laser system, time-resolved hard x-ray detectors have been operating in an energy range from 10 to 500 keV. In this article we will present initial results for the yield and spectrum of the hard x-ray radiation. The concept used on OMEGA can be easily extended to infer the amount of laser energy coupled to suprathermal electrons and to the target for both direct- and indirect-drive implosions on the upcoming National Ignition Facility, as well as to measure the conversion efficiency in high-x-ray-yield experiments.