Thruster evaluation in the MadHex helicon source

Abstract

Summary form only given. The MadHex experimental thruster consists of a 150 cm long, 10 cm inner diameter Pyrex tube connected to a stainless steel expansion chamber 60 cm long and 45 cm in diameter (expansion ratio RE = 4.5) with an axial magnetic field, variable up to 1 kG at the source region that can be operated in nozzle or flat field configurations. An 18 cm long, 12 cm diameter half-turn double-helix antenna is used to excite helicon waves in the source. Ion beams of have been observed at RF power levels of 100-1,000 W in a flowing argon helicon plasma formed in the expanding region of the MadHex helicon source using a magnetic nozzle (RM = 1.44). The effect of flow rate/pressure, RF power and magnetic field strength dependence on the ion beam acceleration, plasma potential, electron density and temperature are explored. The ion energy distribution function (IEDF) is obtained by a two-grid Retarding Potential Analyzer (RPA). The plasma potential is determined by a floating emissive probe. The electron and ion beam distributions and plasma potential variation correspond to a plasma double layer. Additionally, the axial ion velocities and temperatures are observed via argon 668 nm Laser Induced Fluorescence (LIF) and density via a mm wave interferometer at higher RF power levels. The results of fast and slow argon ion beams at lower flow rates (~1.3-2 sccm) with different RF powers are reported in the transition between Pyrex and expanding exhaust regions. The variation of the IEDF in the expansion chamber is also confirmed with RPA results. The specific impulse, Isp(s), force/watt (mN/kW) and efficiency of the thruster will be discussed for the range of RF power, flow rate and magnetic field examined utilizing collisionless plasma theoretical models.