Electron mobility in argon and carbon dioxide

Abstract

Electron drift velocities were determined in argon and in mixtures of argon with carbon dioxide, using media processed to yield a high degree of purity. The measurements were performed at a pressure of 760 torr and a temperature of 25degC. The medium was confined in a cylindrical measuring chamber made of polytetrafluorethylene (10-mm diameter, 10-mm length). The electrodes used to generate electric field were circular, made of stainless steel, and vacuum coated with gold. A layer of ionized gas (approximately 4 mm thick) was created near the negative electrode with a 10-mCi tritium radioactive source. The cell was connected to a pulse generator with a low duty factor, which ensured that most of the time the medium was in the quiescent state. During the active state, an axial electric field was created in the chamber by a short negative pulse applied to the cathode. To assure purity and to facilitate the transport of calibration samples, the gaseous medium was flown from anode to cathode via the chamber (50 mlmiddotmin-1 ). The layer of plasma near the cathode was electrically neutral most of the time since the electrodes were effectively grounded during the quiescent state. The pulsed electric field separated the charge carriers in the plasma layer into fast electronic and slow ionic charges. The time-amplitude dependence reflected the charge separation dynamics and was used for the determination of drift velocities. The velocity data were measured in ultrahigh-purity argon and in binary mixtures of argon with carbon dioxide (from 1.0%v to 6.5%v). In argon, for field intensities Eisin(0,8) kVmiddotm-1, the velocity range was veisin(0,2.8) kmmiddots-1, and for Eisin(8,35) Vmiddotm-1, veisin(0,2.8) kmmiddots-1. In mixtures of Ar-CO2, electron drift velocity depended on the concentration: For field E=8 kVmiddotm -1, veisin(7,18) kmmiddots-1, and for E=35 kVmiddotm-1, veisin(12,24) kmmiddots-1. The data obtained in this study can be used for the determination of the voltage-current characteristics and other parameters of corona discharges. The data are of interest to those who study the physical phenomena in dc and pulsed corona discharges