MPD Arc Thruster with a Permanent Magnet

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With a steady-state operating MPD arc thruster, the discharge current cannot be made as large as is possible with its quasi-steady counterpart. As a result, the electromagnetic acceleration effect produced by the self-induced magnetic field is not large enough. One common approach to overcoming this drawback is to apply an external magnetic field to the discharge region by means of a solenoidal coil. However, this method is not necessarily the best for the thruster system as a whole because of the accompanying increase in its weight and addition of the power supply that is required to produce a given field. The purpose of this study is to overcome this problem through the use of a permanent magnet in place of a solenoidal coil and thereby achieve an MPD thruster with high thruster performance.The thruster performances obtained under typical operating conditions are as follows: When argon was used as the propellant, the specific impulse was 1000 sec at a discharge current of 400 A. That translates into a rather low thrust efficiency of 4.5 %. In contrast to this, when hydrogen was used as the propellant, the specific impulse and thrust efficiency both rose as the discharge current was increased. At a discharge current of 400 A, thrust of 68 mN, specific impulse of 7700 sec and thrust efficiency of 25 % were obtained. It is comparable to the level of efficiency that is obtained with ordinary thrusters when a solenoidal coil is used.