Development of a collisional radiative model of X-ray lasers

A theoretical model of plasma hydrodynamics and atomic kinetics of X-ray la sers is developed to investigate the mechanism of lasing in 4d-4p transitio n of Ni-like ions at short wavelength by the transient pumping scheme. The model is designed for calculations of the ion abundance and soft X-ray gain in the short pulse laser-irradiated plasmas. We develop a compact collisio nal radiative model which combines the detailed level structure of Ni-like ion using atomic data calculated by HULLAC, with averaged levels over a wid e range of charge states using the screened hydrogenic model. The ion abund ance and soft X-ray gain are calculated by postprocessing the temperature a nd density of the laser-produced plasma obtained by the hydrodynamics code. It is found that a large abundance of Ni-like ion can be maintained in the plasma produced from an exploding foil target showing its usefulness as a gain medium of transient collisional X-ray lasers. For improvement of the m odel, sensitivity of the gain and averaged charge to the level structure in cluded in the model are discussed. (C) 2000 Elsevier Science Ltd. All right s reserved.