Use of Auroral Processes in Spacecraft Propulsion: A VASIMR VX-100 Status Report

Plasma physics has found an increasing range of practical industrial applications, including the development of electric spacecraft propulsion systems. One of these systems, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine, applies several important physical processes occurring in the magnetosphere. These processes include the mechanisms involved in the ion acceleration and heating that occur in the Birkeland currents of an auroral arc system. Auroral current region processes that are applied in VASIMR include lower hybrid heating, parallel electric field acceleration and ion cyclotron acceleration. This paper will focus on using two physics demonstration model VASIMR's to study ion cyclotron heating (ICRH). Prior to VASIMR, laboratory simulation of electromagnetic ion cyclotron wave heating has been difficult owing to the difficulty in obtaining efficient antenna coupling for this mode and to the fact that the ions involved only pass through the acceleration region once. The VX-50 and VX-100 VASIMR's use(d) a helicon antenna with 20 kW of power to generate plasma. Both devices then use(d) an RF booster stage that uses left hand polarized slow mode waves launched from the high field side of the resonance. The VX-50 used 2 to 4 MHz waves with 30 kW of power. The VX-100 operates at ~500 kHz, with up to 100 kW of available ICRH power. This paper will summarize results from high power ICRH experiments performed on the VX-50 using deuterium, neon and argon plasma during 2006 and will present preliminary results from the VX-100. Emphasis will be placed on results obtained since the last Fall meeting We have demonstrated ion cyclotron acceleration of a dense (>1019/m3) plasma flow using all three gasses. ICRH loading measurements are consistent with efficient (90%) RF coupling to the plasma. The ICRH experiments have demonstrated that an energy boost of over 500 eV is possible. Early VX-100 results indicate that it should be possible to obtain an exhaust velocity of 40-50 km/s and a momentum flux of several N using argon. An overview of the way forward will be touched on briefly, with some emphasis on the fact that VASIMR is now being developed by private enterprise. The opportunities and challenges of this situation will be reviewed.