Power density in direct nuclear-pumped 3He lasers

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Abstract
The interaction of neutron beams with 3He gas is of interest for nuclear pumped lasers. The effects of spectral dependence of the neutron beam, neutron attenuation in the gas‐filled laser tube, and transport of the charged‐particle 3He(n,p)3H reaction products are treated in detail. An expression for the energy density as a function of position within the tube, tube radius, operating pressure, and neutron fluence is given. The maximum energy density within the optical cavity is achieved when the tube radius a (cm) is given by a=3.26/P where P (atm) is the operating pressure. The variation of radius by 50% above and below optimum will change the energy density at most by 10%, although performance degrades quickly for radii outside this range. If the optimum tube radius is used for each operating pressure, then the power density on the centerline (kW/cm3) is given as ξCL=9.3×10−18Pf0 in a thermal neutron environment of f0 (n/cm2 sec).