Neutral gas temperature of adamantane in a radio-frequency inductively coupled plasma electrothermal micro-thruster using optical emission spectroscopy

Abstract

The gas temperature of adamantane plasma in a 13.56 MHz radio-frequency (RF) inductively coupled plasma was measured using optical emission spectroscopy. Rovibrational band fitting of the Second Positive System of nitrogen gas (N2) from the addition of N2 and Swan system of homo-nuclear carbons (C2) from adamantane dissociation were used to obtain the gas temperature through the rotational temperature under the assumption of rotational-translational equilibrium. The measured temperature ranged from 400 to 700 K, increasing with RF power range from 10 to 100 W and adamantane flow rate from 0.25 to 1 mg s−1, with discharge pressures up to a few Torr. The energy released during adamantane dissociation contributed to a slight temperature increase compared to conventional pure N2 plasma. Adding a large amount of helium (He) acted as a quencher, reducing the gas temperature. In an adamantane-He mixture, the gas temperature remained stable at mid-range power and at lower adamantane flow rates. Justification of gas temperature and a simple power balance model were described. Applications of adamantane spectroscopy include propulsion, plasma processing, and astrophysics, with the inclusion of future studies. Show more