Three-Dimensional Modeling of Magnetic Nozzle Processes

摘要

Simulations of plasma flow through a magnetic nozzle were conducted using the time-dependent, three-dimensional magnetohydrodynamics code, MACH3. The code's grid generation, mesh adaptivity, initial magnetic field, and electric resistivity subroutines were upgraded to improve resolution of physical processes of varying characteristic scale. Modeling of magnetic nozzle flow using constant, classical isotropic, and classical tensor resistivity provides preliminary quantitative depiction of the core-plasma flow, evolution of the magnetic field, and conversion of stagnation enthalpy to directed exhaust thrust energy. For stagnation conditions of 100eV and 0.355MPa, steady-state modeling using helium propellant demonstrates a nearly isentropic expansion through the nozzle to exhaust speeds near 160 km/s. The extent of the contribution from the magnetic diffusion and the mass-flux penetration on the thickness of the current layer is dependent on the selection of the resistivity model. Plasma-field interaction results in a reduction of approximately 50% of the directed axial thrust when compared to a solid-wall nozzle of equivalent Mach number design. At fixed plasma pressure and applied field the exhaust velocity scaled appropriately as the square root of the stagnation temperature.