One of critical issues in fast igniter scheme [1] is energy transport and deposition in a compressed fuel via energetic particles generated by an ultra-intensity laser. In addition to fusion product measurements, a new x-ray spectroscopic method has been expected to provide time- and space-resolved information. We propose to use line radiation arising from inner shell transition in partially ionized tracers to measure temperature distribution of the targets. Moreover, x-ray polarization spectroscopy [2] is useful to obtain anisotropy of fast-electron velocity distribution function (VDF).
X-ray spectroscopic measurement was performed using the PW laser system (130 J in 0.7 ps, 1×10¹⁹ W/cm²) at ILE Osaka University. Cl-HeΑ, -LyΑ, -KΑ, and KΑ's ionization-shift components [3] from the triple layered planar targets involving chroline were observed to derive temperatures using an atomic kinetic code [4]. It was found that a very shallow region (~0.05 μm from the surface) was heated up to 650 eV but the inner region (up to 5 μm) was 100 eV although classical penetration depth of the fast-electron (~500 keV) is about 500 μm in solid CH.
Second, polarization of Cl HeΑ lines from a plasma generated with T6 laser system (120mJ in 130 fs, 1×10¹⁷ W/cm²) were observed. Targets consisted of a double layer of CH and C₂H₃Cl. VDF of hot electrons were obtained from the degree of polarization with respect to the target normal. This correspond to the major axis of fast electron anisotropy. Experimental result clearly shows that, in comparison with Kieffer`s model [2], the shape of VDF is pancake-like (i.e., extended laterally) on the targets surface whereas that becomes beam-like in the 0.05 μm deep region. Details of the experiments and analysis will be discussed.

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