Non-equilibrium and anisotropic K-shell radiation in ultra-intense laser-produced plasmas

Numerical and experimental studies were carried out to gain insight into fast electron transport relevant to fast ignition. Atomic-population kinetics codes associated with K-shell radiation have been developed for quantitative and/or qualitative understanding of the energy deposition process by fast electrons. In the experiments, the Kα lines from partially ionized chlorine were diagnosed as a function of the thickness of an over-layered target, and a dramatic decrease in the radiation yield was found with an increase in the overcoat-thickness of the target at laser intensity of about 1017 W/cm2. The experimental results were analyzed with the use of the numerical calculation codes, resulting in a plasma bulk-electron temperature of ∼150 eV. With the spectroscopy of polarized Heα radiation, the velocity distribution function of fast electrons can be deduced and high polarization was experimentally obtained in low density plasma region (≤10 times the critical density). It is inferred that collimated fast electrons are generated, and show large anisotropy along the propagation direction. (author)