Investigation of high X-ray conversion efficiency Kr filled gas sources at the National Ignition Facility

摘要

We report on the performance of high x-ray fluence Kr K-shell sources that are being developed for high energy density experiments. These targets are 4.1mm in diameter 4.4mm tall hollow epoxy tubes having a 40 mu m thick wall holding 1.5atm of Kr gas. For these shots, the National Ignition Facility laser delivered a nominally constant total energy of approximate to 750kJ of 351nm (3 omega) light at the three power levels [e.g., approximate to 120 (low), approximate to 145 (medium), and approximate to 210 TW (high)]. The Kr K-shell (E-photon = 8-20keV) x-ray radiant intensity and radiant energy (kJ/sr) of these sources were found to increase as a function of laser power but began to plateau at the highest laser power. The Kr K-shell radiant energy increased from approximate to 1kJ/sr at approximate to 120 TW to approximate to 2kJ/sr at approximate to 210 TW. Radiation hydrodynamics simulations predict radiant energies to be always higher than these measurements. The increase in K-shell emission is attributed to its strong dependence on the electron temperature. Electron temperature distributions were inferred from measured He-alpha and Ly(alpha) line emission through the use of a genetic algorithm and Scram modeling. The inferred temperatures from the experiment are 20% to 30% higher than those predicted from modeling.