Spectroscopic Emission Measurements of a Pulsed Plasma Thruster Plume

Abstract : The optical emission spectra of plasmas produced by a Teflon (polytetrafluoroethylene (PTFE)) solid propellant pulsed plasma thruster (XPPT-1) were measured and analyzed. A broad temporally and spatially integrated survey of the emission from 3500 to 7500 angstrom is reported. It is shown that in the PPT discharge energy range surveyed (15 to 45 joule), the species formed do not vary; that is, no new species are formed as the discharge energy is increased. Furthermore, relative line ratios do not vary significantly with energy, suggesting that the bulk thermodynamic properties of the discharge plasma may not be affected by changing the initial stored capacitor energy. A spatially integrated but time- resolved measurement was carried out which shows the single species emission as a function of PPT discharge time. The magnitude of the emission was found to track closely with the PPT current and depend on the discharge energy. Relative line emission intensities are used to determine the degree of excitation equilibrium and establish bounds on the plasma temperature. Spatially and temporally resolved images are used to estimate the plasma streaming velocity from time-of-flight and Doppler-shift techniques.