Study on anisotropic fast electron transport by polarized K-shell radiation in ultra-short intense laser produced plasmas

Polarized Heα of chlorine from ultra-intense laser produced plasmas was calculated. The experiment with 800 nm laser pulses of 100 - 130 mJ in 130 fs was also carried out, and the resultant polarization of time- and space-integrated Heα is so high (≥ 10%). A new time-dependent atomic kinetics code was developed to gain insight into the generation of polarized Heα by fast electron transport relevant to fast ignition. The polarized feature is due to anisotropic electron impacts by fast electrons, and the aspect ratio of fast electron temperatures associated with longitudinal and transverse directions is found to be essential with the numerical calculation. In the calculation, so small polarization (≤ 2 ∼ 3%) is predicted in dense plasma region (≥ 100 times the critical density), which is due to frequent elastic atomic transitions between magnetic atomic sublevels, while high polarization (≥ 10%) is observable in low density region (≤ 10 times the critical density). The collimated fast electrons are generated by electromagnetic instability, resulting in large anisotropy along the propagation direction in low density region