Field Asymmetry and Thrust Control in the GDM Fusion Propulsion System
[Abstract] One of the notable attributes of the Gasdynamic Mirror (GDM) fusion propulsion system is the fact that it lends itself readily to thrust control due to asymmetry in the magnetic field configuration. GDM is a magnetic plasma confinement device that has been proposed as a potential propulsion system. It differs from the standard “collisionless” mirror in that it operates at a much higher plasma density and is generally designed with a large aspect ratio to provide plasma stability. When a plasma is injected into such a device, the electrons tend to escape through the mirrors more readily due to their small mass, leaving behind an excess of ions and correspondingly a positive electrostatic potential. Such a potential accelerates the ions while slowing down the electrons until both species drift outward at equal rate. Of special importance to its value as a propulsion device is the effect of magnetic field asymmetry on such an electrostatic potential. Numerical simulations have been carried out to study this phenomenon and to quantify the role of asymmetry on the overall performance of the system. Experiments will be conducted in order to validate the theoretical and simulation models and to provide a basis for further assessment of GDM as a propulsion device with variable thrust capability.
Improved Physics Model for the Gasdynamic Mirror Fusion Propulsion System
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
Magnetized fuel inertial confinement fusion
A more complete radiation treatment is introduced into the zero-dimensional magnetized fuel inertial confinement fusion (ICF) model of Lindemuth and Kirkpatrick. In particular, the effects of synchrotron radiation and the inverse Compton effect are considered. Only slight changes in the high gain regions of initial shell velocity/initial fuel density parameter space were observed. This more complete radiation treatment removes some objections to the Lindemuth-Kirkpatrick model and lends further support to the idea that magnetic thermal insulation can significantly reduce driver requirements for ICF targets.