Simulations of high power laser-produced multi-keV X-ray source

Abstract

Multi-keV x-ray source produced by high power laser interaction with solid metal target are widely used in high energy density physics research. This work proposed a numerical simulation method for designing the laser plasma X-ray source. The simulation was conducted using a collisional-radiative spectral code combined with one-dimension hydrodynamics code. Quite good agreement was found between the simulations and the experimental results. This work indicates that it is possible to apply this method in x-ray source optimizing.Keywords：Multi-keV x-ray source, backlight image, high energy density physics 1．INTRODUCTIONEfficient multi-keV x-ray source plays an important role in high energy density physics, such as inertial confinement fusion (ICF), x-ray laser and laboratory astrophysics. Highly bright x-ray source is often required in many applications, and this is only possible when the conversion efficiency is great enough with limited laser energy (conversion efficiency defined as the ratio of emitted x-ray energy to laser energy). Most of the articles concerning this issue have concentrated on the influence of the laser intensity [1][2][3][4][5] , and optimization was made to produce higher brightness x-ray source at lower laser driven. At the same time, some novel techniques such as thin foil target and shaped laser pulse have been proposed to increase the x-ray brightness [6][7][8][9] . To obtain a deep vision in these works, detailed hydrodynamic simulations and atomic physics calculations of the x-ray emission are important.This work proposed a novel design of laser-produced x-ray source and conducted a detailed numerical simulation of it. The simulation combined a high temperature plasma emission spectrum code with a one-dimension hydrodynamics code. A simulation of titanium(Ti) He-like x-ray source( ～ 4.75keV) shows that the optimal laser intensity is 4×10 14 W/cm 2 , similar to that found in experiment (5×10 14 W/cm 2 ). It is found that the use of thin Ti-foil target improves the x-ray brightness by 25% and pre-pulse improves another 50%, both are in good agreement with the experimental result. This work indicates a success in designing laser-produced x-ray source with the combination of hydrodynamic simulations and atomic physics calculations. NUMERICAL SIMULATION METHODSThe numerical simulation consists of three steps. First of all, the high temperature plasma emission spectrum code is used to calculate the Ti He-like emission spectrum in different electron temperature and matter density; secondly,