Improved Physics Model for the Gasdynamic Mirror Fusion Propulsion System

Abstract

The propulsion capability of the gasdynamic mirror (GDM) fusion propulsion device was examined in several previous publications without taking into account the electrostatic potential inherent to plasma cone nement in this system. This potential arises as a result of the initial rapid escape of the electrons through the mirrors because of the smallness of their mass. The remaining excess positive charge gives rise to a positive electric potential that slows down the electrons while speeding up the ions until equalization in their axial diffusion is achieved. In a thruster, the energy of the ions emerging from the magnetic nozzle will therefore be enhanced relative to their energy as they leave the mirror by an amount equal to that of the potential. In typical GDM parameters, this effect can translate into signie cant increases in the specie c impulse and thrust produced by the system. Nomenclature Ac = area of plasma core A0 = mirror area D = axial diffusion coefe cient E = electric e eld Ee = electron energy EL = escape energy e = electron charge erf = error function k = gradient scale length L = length of plasma <n l = coulomb logarithm m = particle mass N = particle density n = monoenergetic particle density R = plasma mirror ratio T = temperature V = plasma volume v = monoenergetic particle velocity vth = thermal velocity x = parameter, Eq. (26) z = charge number G = velocity-averaged particle e ux g = monenergetic e ux d = parameter, Eq. (25) m = mobility t = cone nement time y = collision frequency f = electrostatic potential