Frank J. Wessel

Hybrid MHD model for a driven, ion-current FRC

Typical MHD models do not include the effects of a finite-electric field, finite gyro-radius, and gyro-period. The magnetohydrodynamic code, MACH2, is modified in one dimension to account for two-fluid behavior, in order to include these effects during the formation of a “driven”, field-reversed configuration (FRC). The simulation is run for a period of 150 μs, during which time an azimuthal ion current accelerates, the FRC forms, compresses radially and axially, and then begins to decay. Once the FRC is formed, an electron current develops, which sharpens the magnetic-field profile outside the null-field region. The equilibrium that is formed is characteristic of a Rigid Rotor.[1] The simulations also agree with prior experiments,[2] specifically the r-z shape of the FRC and the magnitude of the total current, including the ion and electron flows.

Pulsed-inductive thruster

A new set of pulsed-inductive thrusters (PITs) have been developed for the Flux-Coil-Generated, Field-Reversed Configuration Experiment (FCX) at Tri Alpha Energy, Inc. This paper details their design, simulation, and measured performance. The simulation solves coupled equations for the circuit currents and plasma parameters, including formation and acceleration. The PIT design involves: 5 pulsed-gas valves, a 2-stage Marx generator capacitor bank, a low-inductance parallel-plate transmission line, and a high-current & voltage vacuum feedthrough. The power source provides a 2.5 μs, 1/4-period rise time and 1 Ω impedance. Measurements 1-m downstream from the PIT indicate: n = 1012-1014 cm-3, temperature, Ti = 25-40 eV, and plasma-energy content, Ep = 20-30 J, which are adequate for the FCX.