Investigation of the Instability Phenomena in Hall Thrusters for Practical Application

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The purpose of this study is to clarify the factor of discharge vibration and oscillating current as a problem in the durability on the Hall-current type thruster for space rocket propulsion with compact, light-weight and high thruster performance.The 1kW-class Hall thruster was designed and fabricated to investigate the oscillation problem by measuring discharge voltage and discharge current, and using by electrostatic probes, ion collectors, spectrum analyzers. The dependence of power level, propellant mass flow 'rate on vibration strength and vibration frequency was examined.As the result of the experiment, discharge voltage and space potential were found to be nearly constant in time and oscillatory phenomenon on 10〜30kHz band was observed mainly on the discharge current. In addition, both the experimental and numerical results indicated that this discharge oscillatory phenomenon originates from vibration of the ion beam current, vibration of the plasma production rate. Also, the plasma density oscillation at the similar frequency was indicated as a result of the vibration measurement of ion saturation current in the acceleration channel.The theoretical model was newly constructed by the assumption of a small disturbance which propagates on the basis of conservation formula of neutral particle density and plasma density in having a wave number at the starting point.From both the experimental and theoretical results, it was found that the oscillation phenomena in Hall thrusters are caused mainly by ionization instability occurred in the plasma acceleration channel.