Volume and surface propellant heating in an electrothermal radio-frequency plasma micro-thruster

Abstract

The temporal evolution of neutral gas temperature over the first 5 min of operation for an electrothermal radio-frequency micro-thruster with nitrogen (N2) propellant was measured using rovibrational band matching of the second positive N2 system. Three distinct periods of gas heating were identified with time constants of τ1 = 8 × 10−5 s, τ2 = 8 s, and τ3 = 100 s. The fast heating (τ1) is attributed to volumetric heating processes within the discharge driven by ion-neutral collisions. The slow heating (τ3) is from ion neutralization and vibrational de-excitation on the walls creating wall heating. The intermediate heating mechanism (τ2) is yet to be fully identified although some theories are suggested.