X-ray polarization spectroscopy to study energy transport in laser produced plasma at 10$^{18}$ W/cm$^{2}$

In ultra-high intensity laser produced plasma, velocity distribution function (VDF) of hot electrons is highly anisotropic while that of cold electrons in the bulk plasma is isotropic. X-ray polarization spectroscopy has been used to measure directly VDF of hot electrons in the plasma at 10$^{17}$ W/cm$^{2}$ [1, 2]. A new measurement was made at 10$^{18}$ W/cm$^{2}$ using Alis\'{e} facility at CEA/CESTA. Chlorinated triple-layer targets were irradiated and Cl He$\alpha $ line was observed with an x-ray polarization spectrometer. Experimental results and comparison with the model prediction will be discussed using a time-dependent atomic kinetics code for polarized Cl He$\alpha$ radiation [3]. \newline [1] H. Nishimura, et al., \textit{Plasma Phys. Cont. Fusion}\textbf{47}, B823 (2005). \newline [2] Y. Inubushi, et al., JQSRT \textbf{99}, 305 (2006); \textit{Phys. Rev. }\textbf{E 75}, 026401 (2007). \newline [3] T.Kai, et al., \textit{Phys. Rev} \textbf{A 75}, 012703 (2007), T. Kawamura, et al., submitted.