Probe measurements of plasma properties inside an experimental hall thruster

An experimental Hall thruster was operated under various operating conditions with two different magnetic circuit configurations generating different gradients of the magnetic field strength along the channel. In addition to the voltage versus current characteristics and thruster performance, the floating potential distribution along the thruster channel was measured with a movable Langmuir probe. It was found that while a smaller gradient of the magnetic field profile results in a longer acceleration region, the length of this region is almost not affected by variations of the discharge voltage or the mass flow rate. It follows from the measured discharge characteristics and thruster performance that smaller ion and current losses take place in the case of the stronger magnetic field gradient, i.e., when the acceleration region is short. However, at small mass flow rates there is a certain value of the discharge voltage above which the propellant utilization becomes larger when the acceleration region is longer. At these operating conditions, the thruster performance, namely, specific impulse and thruster efficiency, is almost not affected by the magnetic field distribution.