Global Modeling of N2O Discharges: Helicon Plasma Thruster Application

A global (volume averaged) model pertaining to N2O discharges is used to design and to study electric propulsion applications, especially helicon plasma thrusters fed with pure N2O and also with N2/O2 mixtures including air. Results obtained for N2O feeding are discussed and compared to those pertaining to an air-like N2/O2 mixture feeding. An interesting similarity is observed. Comparison of the N2O model results versus those of Ar shows lower ionization percentage with higher electron temperature for N2O propellant. 1. Introduction A global (volume averaged) model (GM) conceived for modeling of discharges fed by N2O and by N2/O2 mixtures including 4？:？1 [N2]？:？[O2] air-like ones [1] is applied to electric propulsion devices in case of pure N2O and of N2/O2 feeding. The main results obtained by this model allowing to characterize the central “core” region part of helicon plasma thrusters (HPT) are presented and discussed. The selected dimensions are the same with those of a previous work addressing an Ar fed HPT [2], namely a cylinder of length ？cm and radius ？cm with plasma “core” radius about 0.3？cm. Functioning is restricted in a rather low pressure region, of 3？mTorr up to 30 mTorr, and the absorbed power varies from 25？W up to 1000？W. Note that both pressure and power ranges have been here enlarged in comparison with the values used in [2] treating an Ar fed HPT which spanned only a 2？mTorr to 10？mTorr region for the pressure and 25？W to 150？W for the absorbed power. The type of modeling applied here is quite analogous to the one we used recently to design and characterize the Argon fed HPT of [2] but takes into consideration detailed atomic and molecular structure and collision data concerning N2O and its products. Although the present paper is oriented towards a rather hot thruster plasma region, modeling of the plasma contained in the “mantle” external part of the thruster and/or of other low temperature plasma applications, quite similar to the one applied in the Plasma Reactor (PR) case of [2] can be obtained in a straightforward manner. Besides evaluation of and of species densities present in the “core” region in case of N2O feeding, our GM is further applied to model an air-like mixture fed HPT thruster. This allows for an adequate design and study of air fed HPT thrusters, giving the and the densities of the species in various conditions. Comparison of N2O fed HPT properties to those of air fed ones and also to those fed by Ar has been made possible by using the present model and the one described in [2]. Results for feeding of HPT by