Experimental investigation of high velocity neutral flow interaction with a magnetized plasma

Abstract

Plasma aerocapture is an orbit insertion method that leverages a magnetic dipole plasma to generate drag by ionizing, capturing, and deflecting atmospheric flow. Key physical assumptions about energy and momentum exchange during aerocapture are tested here by a novel experiment that characterizes the interaction between a high velocity free molecular flow and a magnetized plasma. A neutral beam source accelerates ions from a helicon plasma to a conductive plate, neutralizes them, and reflects them as a collimated flow. A hollow cathode plasma with an applied axial magnetic field of 1 kg acts as the target for the flow. It is found that interaction with the flow causes an increase in both density and temperature of the target plasma by up to a factor of two. The voltage required to operate the hollow cathode at a fixed current is reduced by up to 5% while the neutral beam is operating, suggesting power deposition by the flow. A 0D power balance model is invoked to show that flow kinetic energy is absorbed by the plasma at a rate of up to 50% of the hollow cathode power. The absorbed power correlates linearly with an electron temperature increase of up to 100%, indicative of electron heating by flow kinetic energy transfer. Deflection of the flow by the plasma is not resolved due to extraneous forces on the measurement device and uncertainties in plasma properties. Using the results found here, it is shown that the experiment can feasibly scale to demonstrate significantly higher energy and momentum transfer as required for a plasma aerocapture proof-of-concept.