Momentum and Heat Flux Measurements Using an Impact Target in Flowing Plasma

Abstract

An impact target plate was used to determine the momentum and heat flux quantities from a helicon plasma source. The plasma source is the first stage of the Variable Specific Impulse Magnetoplasma Rocket, which uses radio frequency waves to create and energize a flowing plasma. The momentum and heat flux quantities are determined separately and agree favorably. They also agree with expected flux quantities calculated from the plasma parameters determined by other probes. The momentum and heat flux quantities were obtained at two axial locations in the exhaust or magnetic nozzle region of the device using helium and argon propellant. Only data from the plasma source are used, which shows that the plasma source does produce a flowing plasma with significant momentum. The flux data at the two axial locations verify the increase in momentum as the plasma flows through the diverging magnetic field in the magnetic nozzle region. Although the axial location for maximum momentum (or thrust) was not determined, forces of several millinewtons were measured for a combined neutral particle and plasma flow. The ionization fraction for these data was approximately 22 %. Neutral particles entrained in the flow provided a significant part of the flow momentum thereby contributing to the potential thrust. The technique of measuring the momentum flux and heat flux in a flowing plasma is described.