The Onset of the Magnetized Pulsed Vacuum Arc: a Promising Way for High Efficiency Propulsion

Vacuum arcs nowadays are used in the wide range of applications including high current electronics, thin films deposition, particle accelerators and advanced plasma propulsion. Minute vacuum arc thrusters can be attractive for some applications such as small satellites (CubeSats) propelling, and the thrust level of such thrusters can be remarkably enhanced by implementing a magnetic field. However, for such applications as orbit raising or interplanetary missions, the overall performance including thrust and lifetime of such thrusters requires even further enhancement. This can be done by the adding a second acceleration stage to the thruster. Recently, we proposed a possible approach that we called a Micro-Cathode Arc Thruster with Magneto Plasma Dynamical second stage (μCAT-MPD) with applied magnetic field that can be created by either permanent magnet or magnetic coil. The first stage will produce the small shot of plasma, while the second MPD stage will generate even more plasma and accelerate it to the higher velocities by the j x B force. MPD principle of plasma acceleration, in our opinion, prevails over the gridded ion and Hall thruster concepts since it does not require ion-adsorbing and eroding grids, high voltages and cathodes-neutralizers with limited lifetime.Investigating this new plasma thruster, it has been revealed that such a magnetized pulsed two-staged discharge has an onset: its thrust and total charge of expelling ions rapidly jump after certain threshold dc voltage applied to the accelerating (MPD) second stage. Using independent experimental methods, we observed that the mentioned effect allows increasing the thrust (in several tens of times) simultaneously with thrust-to-power ratio (in several times). This opens up the perspectives of creation of new type of miniature and low-power plasma thrusters for small satellites propulsion.

I. Introduction

ELECTRIC propulsion systems for propelling small satellites as cubesats are actively developing nowadays, which is caused by many reasons, including the high demand in small low-power satellites with extended lifetime, and the progress in the microelectronics [1], [2]. Among the most common low-power propulsion systems such thrusters as electrospray [3], Hall effect [4], rf [5], and vacuum arc [6], [7] thrusters can be highlighted. A micro-cathode arc thrusters (μCATs, developed in the Micropulsion and Nanotechnology Laboratory (MpNL) of the George Washington University), consisting of coaxial anode-cathode electrode system, can provide average thrust of up to tens of micro-newtons, thrust-to-power ratio of around several μN/W, during around one million pulses. However, some space applications require higher values of thrust and thrust-to-power ratio. In our previous work [8] we proposed a concept of the improvement of μCAT performance by a more powerful second stage based on an applied-field Magneto Plasma Dynamical (MPD) concept, for additional increase of its thrust level. In this paper we report our recent progress in research of physical processes in two-staged μCAT-MPD thruster both in permanent and pulsing magnetic field configurations. We also pay here a special attention to description and discussion of "activation" of the second MPD stage resulting in the drastic improvement of performance (i.e. significant increase of its thrust, thrust-to-power ratio and efficiency).