Plasma Flow During RF Discharges in VASIMR

The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) plasma source consists of a helical antenna, driven at frequencies of 4 to 19 MHz with powers up to 1 kW, in a magnetic field up to 3 kG. Helium is the current test gas, and future experiments with hydrogen are planned. Plasma density and temperature profiles were measured by a reciprocating Langmuir probe, and plasma flow profiles were measured with a reciprocating Mach probe. Both probes were located about 0.5 m downstream from the helical antenna. The plasma source operated in capacitive and inductive modes in addition to a helicon mode. During capacitive and inductive modes, densities were low and plasma flow was < 0.5 Cs. When the plasma operated in a helicon mode, the densities measured downstream from the source were higher [10(exp 12) / cubic cm ] and plasma flow along the magnetic field was of the order Mach 1. Details of the measurements will be shown.