Study of fast electron transport in hot dense matter using x-ray spectroscopy

Experimental study on energy transport in ultra-high intensity laser plasma was made. X-ray emission from a triple-layer target irradiated at 10 19 W cm −2 was observed with x-ray spectrographs, monochromatic imagers and an x-ray polarimeter to provide a temperature profile in the depth of the target, lateral extension of the heated region and the velocity distribution function of hot electrons. For PW plasma, a very shallow region (∼0.5 µm from the target surface) was heated up to 650 eV but the temperature of deeper region (up to 5 µm) was around 100 eV. These depths are much shorter than those expected from the classical penetration of the hot electrons. The localized energy deposition is also found for the plasma generated at 10 17 W cm −2 , and the degree of polarization of the helium-like Cl–Heα line (1s 2 1 S 0 –1s2p 1 P 1 ) from the surface region is polarized parallel to the surface direction whereas that from a deeper region is in perpendicular to it. The experimental result is analysed using a two-dimensional Maxwellian distribution function for hot electrons. Beam-like distribution was found in the depth of plasma.