Experimental and theoretical investigation of EUV radiation behavior of laser-produced Zr plasmas

Abstract

Extreme ultraviolet radiation of laser-produced zirconium (Zr) plasmas were measured in the 6.7–14.7 nm region using a spatio-temporally resolved laser-produced plasma spectroscopy technique. At shorter wavelengths, the spectrum was dominated by several lines attributed to the 4s-(6p,7p,8p) transition arrays of Zr6+ to Zr10+ ions. For the 4s-5p and 4p-6 s transitions, the spectral lines concentrated near 11.18 nm and smoothly move towards longer wavelengths with decreasing ion-charge-state, which are experimentally and theoretically investigated. The Hartree-Fok (HF) method with relativistic corrections (HFR) using the Cowan's codes and Flexible Atomic Code (FAC) were used to calculate and interpret the observed spectra, respectively. At relatively high temperatures, lines from 3p-3d transitions in Zr13+ and Zr14+ ions have been found to have an important contribution. A number of spectral lines are established in this study for the first time. Besides the atomic structure calculations, a numerical computation based on the assumption of a normalized Boltzmann distribution among the excited states associated with a steady-state collisional-radiative model (CR), has also been performed to obtain the plasma parameters by comparing the experimental and simulated spectra. The corresponding dominant ion stages and ion fractions for different ion stages were obtained. We have also provided the evolution of rate coefficients as a function of electron density and electron temperature. We reproduced synthetic spectra which are in good agreement with the experiment. Temporal and spatial evolution behavior about plasma parameters have been analyzed. The variation of electron plasma frequency and skin depth with plasma temperature were introduced. The results may be beneficial for spectroscopic diagnostics of hot plasmas in tokamak and fusion research.