Diffusion processes and sheath structure in the near-anode region of an arc discharge in the presence of a transverse magnetic field

Abstract

Summary form only given, as follows. Understanding the nature of processes occurring at the electrodes of DC plasmatrons is an important aspect of the field of electric propulsion. Such an understanding yields information on engine lifetime which is related to erosion processes occurring at the electrodes and on engine efficiency which is related to energy loss phenomena occurring at the electrodes. This study attempts to understand the nature of power deposition into the anode of an argon arc discharge in the presence of a transverse magnetic field. The ratio of the transverse diffusion coefficient to the parallel diffusion coefficient, D/sub I//D/sub II/, in the near-anode region is measured experimentally via electrostatic probes. In addition, the behavior of this parameter is correlated with measured anode sheath voltage which has been shown to be directly related to energy loss phenomena occurring in certain electric propulsion devices. Along with the diffusion coefficient data, spatial profiles of electron and ion number density, electron temperature, and plasma potential profiles have also been measured. In addition to the electrostatic probe measurements, spatially resolved spectroscopic measurements have also been obtained in the near-anode region. Spatial variations in the intensity of argon ion emission lines near the surface of the anode have been obtained. Such data provide a qualitative measure of the spatial extent and behavior in general of the anode sheath as a function of magnetic field and discharge current. Data obtained from the above mentioned studies shed light on why the measured large positive anode fall voltages develop.