MPDスラスタ内における電熱・電磁加速モード間の遷移に関する研究

Abstract

It is widely known that a self-field MPD thruster changes from an electrothermal acceleration mode to an electromagnetic one as the discharge current is increased. Such transitional behavior is numerically studied with argon propellant using a two-dimensional TVD Lax-Friedrich scheme incorporating multiple ionization processes. As the discharge current J is increased from 4 to 10kA under a mass flow rate of 0.8g/s, a steep rise of the voltage, which indicates the transition, occurs between low and high current modes of operation around J=7kA, which is equivalent to the Alfven’s critical ionization current. The steep voltage rise is attributed to the increase in the work of the Lorentz force around the cathode. The radial distributions of the heavy particles and electrons are examined and compared with the past experimental results. Additionally, in the electromagnetic mode, the ratio of the ionization energy to the input power decreases with increasing input power, and the maximum ratio of the kinetic energy to the input power is 0.57. This high thrust efficiency can be attributed to the idealized model, in which the effects of the sheath as well as the heat loss to the electrodes are neglected.