Freely-expanding spherical flow from the spot source heated by beam injection

The free expansion of a spherical flow generated from a spot source can be described in terms of the polytropical process. It is well known that electron beam injection to the spot source is quite effective measure of raising the temperature of the limited surface. Namely, the energy demand to accelerate the freely expanding flow is supplied from the electron energy. In this paper, the heat transfer into the spot source due to electron beam injection, the driving force of the expanding rarefied gas, was calculated. In terms of the entropy-increase model, the polytropic coefficient was nearly 4/3, which corresponds to that of the homogeneously expanding flow, whereas the specific heat of the monoatomic viscous gas is 5/3. Hence, the flow velocity in the presence of electron beam heating was evaluated to be larger than that of the isentropic flow by a factor of nearly two. Furthermore, the dependence of the accelerated flow velocity upon the electron energy, current density and atomic number density at the source was discussed here. (author)