An investigation into the role that a transverse magnetic field plays in the formation of large anode sheath potentials

A 9.25 A low-pressure (45–55 mTorr) hollow cathode arc discharge has been used to simulate plasma processes that occur at the anode of magnetoplasmadynamic accelerators used for space propulsion applications. The interest in the near-anode region is related to findings of past research, which indicate that large anode sheath potentials can drive as much as 70% of the input electrical power into the anode, thus degrading thrust efficiency. Presented here are results that essentially characterize the behavior of the near-anode plasma as a function of a transverse magnetic field. Plasma diagnostics included single Langmuir probe techniques, emission spectroscopy, and water calorimetry for anode heat flux measurements. Phenomenological arguments based on measurements taken suggest that observed changes in anode fall voltage are related to variations in the measured local electron number density as the magnetic field is varied. This behavior is attributed to the variations in the measured ionization rate, which is shown to be a nonlinear function of transverse magnetic field.