Pulsed expansion of plasma in a magnetic thruster.

摘要

The inertial confinement fusion (ICF) pulse rocket is capable of both extremely high specific impulses and high thrust-to-weight ratios by virtue of intermittent nuclear fusion energy production isolated from the vehicle structure. The thruster of the rocket, which converts an initially isotropically expanding ICF debris plasma into a directed pulse jet exhaust, is to be fabricated out of magnetic fields created by current coils attached to the vehicle. Thrust is obtained through the property that good conductors exclude magnetic fields.; Because of the highly dynamic behavior of the flow, which is bounded by an interface whose motion is unknown a priori, the first problem which must be investigated is that of the bulk flow. Numerical simulations of the bulk flow process were conducted under both the thin-shell and the classical hydrodynamic approximations.; In the former approach, all of the plasma is assumed to be collected into an azimuthally symmetric perfectly conducting thin shell at the interface due to interfacial pressure application. These calculations showed that, under idealized conditions, promising propulsive efficiencies could be obtained for a range of field-to-plasma energy ratios and thruster geometries.; In the latter approach, the plasma is approximated as an unmagnetized perfectly conducting fluid obeying the laws of classical hydrodynamics. The hydrodynamic codes (both 1-D and 2-D) employed an advanced Classical Particle-In-Cell (PIC) scheme, and were successful at capturing interface motions self-consistently. The shock arising from the interface deceleration was also captured correctly. One-dimensional planar-geometry simulations gave results which matched well with analytical calculations for such processes as free expansion into a vacuum and shock-tube problems. The formation of a shell-like structure originating from the interfacial regions was observed in simulations of large expansion ratio flows carried out in two dimensions, although these "shells" did not necessarily stay at the interface.; The idealized bulk flow analyses in this work are hoped to serve as a basis for more detailed studies of how the flow will behave with a real plasma and to help assess the feasibility and design issues of the device.