High-Efficiency Compact Toroidal Plasma Acceleration Using Annular Helicon Pre-Ionization For High-Power, High-Specific Impulse Electric Space Propuls

Electromagnetic propulsion using compact toroidal plasmas is ideal for high-thrust, high-Isp missions since velocities and densities are not space charge limited, the self-field structure does not suffer magnetic detachment problems and the inductive electrode-less nature has superior lifetime. This STTR builds on a long history of research by integrating an annular helicon source with a conical theta-pinch field-reversal plasma accelerator. The traditional approach using the pulsed theta coil for both ionization and acceleration has poor efficiency since a large fraction of pulse energy is wasted to plasma magnetization during the ionization phase. Preionization with DC glow discharges improve performance at the expense of lifetime. Helicon systems yield highly conductive initial plasmas (10^12-13, 3-5eV); however, the density is peaked on the centerline far away from the theta coil. This large distance results in very poor mutual inductance with the plasma secondary. The annular helicon offers a potential solution by establishing a highly-conductive plasma shell near the outer wall for superior transformer action and high pulse energy utilization for axial plasma translation. The Phase I goal of this STTR project is to evaluate the concept for Phase II moderate-power evaluation (10-20kW) through modeling and experiment leveraging strengths and capabilities at both institutions.