Evaluation of compact ECR plasma source for thruster applications

Abstract

The performance of a plasma thruster is assessed for efficient propulsion by analyzing the unique downstream characteristics of plasma produced by a Compact ECR Plasma Source (CEPS). For this, data presented in an earlier publication (Ganguli et al 2016 Plasma Sources Sci. Technol. 25 025026), wherein plasma produced in the CEPS is allowed to flow into a small stainless (SS) steel chamber, are revisited so as to throw new light on the nature of the plasma flowing out from the CEPS. It is shown that the normalized axial density profiles of the bulk and warm electrons (on account of their being strongly magnetized) follow closely the normalized profile of CEPS axial magnetic field expanding into the SS chamber, yielding the scaling n/B ≈ constant over a wide range of pressures. In addition, the bulk electrons obey the Boltzmann relation indicating that they are in thermal equilibrium and also satisfy the double adiabatic equation of state. Analysis of the data using a simple model that takes into account plasma flow, ambipolar electric field and collisions is also presented. It is shown that efficient thruster operation is possible only at low pressures (≤0.1 mTorr). Empirical estimates for argon yield peak thrusts of ∼2.5 mN (at 0.5 mTorr) and 7.5 mN at 0.05 mTorr, for moderately low microwave powers of ∼500 W. Physics issues relevant to CEPS are considered for improvements in future thruster designs.