Experimental Status of the Development of a Variable Specific Impulse Magnetoplasma Rocket

The Advanced Space Propulsion Laboratory (ASPL) is developing a Variable Specific Impulse Magnetoplasma Rocket (VASIMR) using a Radio Frequency (RF) heated magnetic mirror operated asymmetrically. The system comprises of three stages: 1) plasma ionization and injection into the magnetic system; 2) ion heating by action of Ion Cyclotron Resonance Heating (ICRH); 3) plasma exhaust through a magnetic nozzle. The central experimental device is a small versatile tandem mirror configured system. The system can also be easily reconfigured to operate as a simple mirror. The total length of the device is 3.2 m, and the maximum magnetic field is 3.0 T. The exhaust end connects to a 5 m vacuum chamber where we are installing a 40,000 liter/second pumping capacity. Radio frequency power is available at approximately 3 MHz at up to 200 kW. A set of plasma diagnostics is being developed and installed, starting with two fast reciprocating probes, one quadruple Langmuir and one Mach.² We are now evaluating the use of a helicon³ RF plasma source for an efficient ionization stage of the system. Initial results from experiments using a single double-half turn antenna are presented. In addition, we are exploring the use of a Lorentz Force Accelerator (LFA) as a plasma injector source.⁴