Characteristics of gas dynamics of flow lasers excited by fission fragments of uranium nuclei

The conceptual design of a nuclear-pumped cw laser is put forward. Alternation of laser cells with plane uranium layers and heat exchangers (radiators) in a shared gas loop can reduce the gas velocity down to ~10 ms^-1. The results are reported of an investigation of optical inhomogeneities which appear in He and Ar due to excitation of the active medium in a prototype flow laser. It is shown that, in a section perpendicular to the plane of the uranium layers, a pumping inhomogeneity creates a positive parabolic gas lens and in a section parallel to these layers an optical gas wedge is formed. A vortex zone is observed in the gas flow at the exits from heat exchangers. Simulation experiments demonstrate that this effect increases tens of times the thermal diffusivity of the gas and results in considerable refractive losses of radiation in the effective heat-exchange region. Methods of compensating for optical inhomogeneities and for reducing the influence of vortices are proposed.