Polarization of Heα Radiation due to Anisotropy of Fast-Electron Transport in Ultraintense-Laser-Produced Plasmas

An atomic kinetics code is developed to gain insight into the generation of polarized Heα by fast electron transport relevant to fast ignition. The calculation predicts a very small polarization in the dense region (≥100 times the critical density) due to frequent elastic transitions between magnetic sublevels, while high polarization is observable in the low density region (≤10 times the critical density). It is inferred that fast electrons are collimated due to electromagnetic instability, resulting in the generation of anisotropic fast electrons along the propagation axis in the low density region