Measurement of Low-Pressure Plasma Parameters by the Floating Double Probe Method for Dry Air and Helium Gas in a Capillary Glow Discharge

Abstract

The electrical continuous glow discharge is in the capillary tubes. It has gained great interest especially in the applications of liquid crystals as well as display plasmas and soft x-ray lasers. In the present work, an electrical discharge system was designed consisting of a capillary tube and two electrodes. The cathode takes on a hollow geometric shape from nickel material to obtain a high current density. The anode electrode is a tungsten material. The inter-electrodes distance was taken as 12 cm. The floating Langmuir double probe was used as a diagnostic Tool to measure the plasma parameters at different ranges of gas pressure for dry air and helium as working gases. The current-voltage characteristics of the double probe were measured at gas pressure 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 torr. All measurements are conducted at a constant power of 0.6 watt. Electron temperature and ion saturation current were extracted from the I-V characteristics curves. The electron density, Debye length, and plasma frequency were calculated. It was observed that the electron temperature decreases with increasing working gas pressure. The influence of pressure on electron density and ion saturation current gave a clear similarity to the variation in them with pressure in both gases used. Comparisons of the effect of pressure on plasma parameters in working gases were illustrated. The results were in reasonable agreement with previous research.