Nuclear experiments with petawatt class lasers

Summary form only given. A number of experiments using the petawatt laser system at LLNL have now been performed to examine the creation of hot electrons and their use in the fast ignition approach to ICF. By changing the experimental conditions, the electron spectrum can be shifted towards higher energy, even in solid density plasmas. In this regime the laser-target interaction is dominated by the enormous light pressure and relativistic effects. New instruments and techniques are required to diagnose the plasma conditions because many traditional plasma diagnostics are not longer effective. High-field magnetic dipole spectrometers were fielded to measure the electron spectrum emerging from the back of the target and orthogonal to the laser axis. The dispersed electron spectrum is recorded as tracks in a standard emulsion. Electrons were observed at energies extending above 90 MeV, however the bulk of the distribution was in the range of /spl sim/5-15 MeV where the emission was found to be forward directed. High-energy bremsstrahlung X-rays generated by these electrons in the gold target produced photonuclear reactions in both the gold and surrounding copper target-holder producing activation and transmutation to platinum and nickel daughter isotopes. Post-shot g-spectroscopy was used to examine the production of these and other radioactive isotopes via photonuclear reactions. The threshold gamma-ray energy for photoactivation of the gold and copper indicates a large flux of high-energy bremsstrahlung. A gamma spectrum and decay curve are shown. In addition to these data, neutron spectra and other high energy X-ray spectra are also presented. Together, these diagnostics are providing us the first glimpse into this new regime of laser-matter interactions.