A Microwave-Excited Microplasma Thruster: Plasma Diagnostics, Performance Testing, and Numerical Analysis

Decreasing the scale of propulsion systems is of critical importance on the development of microspacecraft. This paper is concerned with an application of microplasmas to a microthruster, presenting some experimental and numerical results. The microthruster consists of a cylindrical microplasma source 10 mm in length and 1.5 mm in inner diameter and a conical micronozzle fabricated in a 1.0 mm thick quartz plate with a throat diameter of 0.2 mm. The microplasma source produces hot plasmas by 4-GHz microwaves in the pressure range from 5 to 50 kPa, and then the micronozzle converts such high thermal energy into directional kinetic energy as a supersonic jet. Plasma diagnostics and performance testing showed that the electron density, rotational temperature, thrust, and specific impulse obtained were 10$^{19}$ m$^{-3}$, 1000 K, 1.1 mN, and 73 s, respectively, at an Ar/N$_2$ gas flow rate of 50/0.5 sccm and an input power of 9 W. Comparison with a numerical analysis implies that the micronozzle has an adiabatic wall rather than an isothermal one.