On the optimization of operating pressure for a nuclear pumped laser excited by 3He(n, p)3H reaction products

Abstract

In the nuclear pumped laser, passage of the energetic nuclear fragments through gas causes a non-uniform energy deposition. This spatial non-uniformity induces gas motion, which results in density hence, refractive index gradients. Since the refractive index gradient of the gas determines the degree of beam refraction as it propagates through the cavity, refractive index gradient adversely affects the resonator stability and beam quality. Therefore, optimal gas parameters should improve optical homogeneity in addition to output power. Refractive index gradient are here considered to be a measure of optical inhomogeneity and its variations with tube parameter are examined to ensure the necessary optical quality of the supplied gas. Spatial and temporal variations of normalized refractive index gradients in the 3He gas excited by 3He(n,p)3H reactions are calculated by using the density field obtained from the previously reported dynamic model for energy deposition for various operating pressures and tube radii. Additionally, variation of power deposition per pulse with the operating pressure and variation of average power deposition density with tube diameter are calculated and used in determining optimal parameters, as a measure for improving the output power. The optimal operating pressure and tube size, from the point of view of power deposition and optical homogeneity, are determined for the present conditions. Calculated results are obtained for a closed 3He-filled cylindrical laser tube, with a maximum thermal neutron flux of 8×1016n/cm2 sn, by using characteristics of the TRIGA Mark II Reactor at Istanbul Technical University (ITU).