Discharge features in a steady-state nitrogen arcjet engine with an expansion nozzle

Nitrogen discharges in a 10-kW-class water-cooled arcjet engine were studied by means of spectroscopic diagnostics. The atomic excitation temperature and electron density in the constrictor increased from 15,000 to 18,000 K and from 1×10¹⁵ to 2×10 ¹⁶ cm^-3, respectively, with input power levels of 7-11 kW. An increase in the mass flow rate raised the electron density because of enhanced thermal pinch effect of the arc column. In the expansion nozzle, the pressure and electron density decreased drastically downstream, and therefore the plasma was expected to be in high non-equilibrium. The N₂⁺ vibrational temperature reached about 6,000 K at the nozzle exit, and the N₂ ⁺ rotational temperature decreased gradually resulting in a range of 1,000-2,500 K