Direct measurement of neutral gas heating in a radio-frequency electrothermal plasma micro-thruster

Direct measurements and modelling of neutral gas heating in a radio-frequency (13.56 MHz) electrothermal collisional plasma micro-thruster have been performed using rovibrational band matching of the second positive system of molecular nitrogen (N₂) for operating pressures of 4.5 Torr down to 0.5 Torr. The temperature measured with decreasing pressure for 10 W power input ranged from 395 K to 530 K in pure N₂ and from 834 K to 1090 K in argon with 1% N₂. A simple analytical model was developed which describes the difference in temperatures between the argon and nitrogen discharges.