Experimental and simulation studies on radiative properties of uranium planar target coated with an ultrathin aluminum layer

An ultrathin aluminum (Al) layer is proposed to be coated on the surface of the uranium (U) planar target for preventing the oxidization of U and optimizing the hard x-ray spectrum. Comparative experiments using several planar targets with different materials are implemented on the Shenguang-III prototype laser facility to study their radiative properties. Under the laser intensity of 1.0×10^15 W/cm2, we observe that the U target coated with 30 nm-thick Al produces almost the same peak intensity of the total x-ray flux and decreases the hard x-ray fraction by 38.5% compared to the U target coated with 100 nm-thick gold. Simulations using XRL2D (two dimensional radiation hydrodynamic code) interpret the measured results and indicate that the radiative property of Al-coated U approaches that of pure U, which theoretically has a high laser to x-ray conversion efficiency and a quasi-Planckian spectrum. Based on our analysis, Al-coated U is a promising material of the ignition hohlraum and should have many applications in high energy density physics.