Investigation of a Light Gas Helicon Plasma Source for the VASIMR Space Propulsion System

An efficient plasma source producing a high‐density (∼1019 m−3) light gas (e.g. H, D, or He) flowing plasma with a high degree of ionization is a critical component of the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) concept. The high degree of ionization and a low neutral background pressure are important to eliminate the problem of radial loss and axial drag due to charge exchange. We have performed parametric (e.g. gas flow, power (0.5 – 3 kW), and magnetic field studies of a helicon operating with gas (D2 or He) injected at one end, with a high magnetic mirror downstream of the antenna. The downstream mirror field has little effect on the exhaust flux up to a mirror ratio of 10. We have explored operation with a cusp and a mirror field upstream. The application of a cusp increases the plasma flux in the exhaust by a factor of two. Plasma flows into a large (5 m3) vacuum (< 10−4 torr) chamber at velocities higher than the ion sound speed. High densities (∼ 1019 m−3) have been achieved at the...