Experimental study of the ionization region of the Minihelicon Plasma Thruster

The high-resolution passive emission spectroscopy is used to investigate ionization region of the Minihelicon Plasma Thruster (MPT) [1]. The region was shown to be just several centimeters long axially for the noble gas propellants [2]. However, it is visibly longer for the nitrogen and air. We use an improved NUV-NIR system with resolving power approaching 10M, which allows capturing Doppler shifts with high precision. Several strong ionic lines and molecular ion bands are collected using angled optical collimators mounted on a linear stage. The line- and band-shapes are then used to analyze the structure of the gas/plasma flow in the ionization/acceleration region of the MPT. [1] O.Batishchev, Minihelicon Plasma Thruster, IEEE Trans. Plasma Science, 37 (8) 1563, August 2009; [2] T.Matlock, Emission Spectroscopy for the Study of Electric Propulsion Plasmas, MS Thesis, MIT, June 2009; [3] A.Hyde, O.Batishchev, A high-resolution spectroscopic system for remote measurement of plasma parameters, Review of Sci. Instr. 91(063502), June 2020.