Measurement of electron density and temperature in an annular magnetically confined cold-cathode plasma of helium by optical emission spectroscopy

Abstract

Magnetically confined cold-cathode plasmas in monatomic gases like helium can be used in a variety of devices and applications. In this paper, the radial distribution of electron temperature and electron density in cold-cathode helium plasmas constrained by an annular magnetic field were studied by optical emission spectroscopy. Helium plasma was generated under different pressures (7.5, 10, and 20 Pa) and values of current (23.5 and 33 mA). The spectral lines of He I 667.8 and He I 501.6 nm were studied and the Stark broadening method was applied to obtain the radial distributions of electron temperature and electron density. The results indicate that higher radial gradients or peak values of both electron density and electron temperature could be achieved with increasing operating pressures and discharge currents. It was found that the electrons were mainly concentrated in the area of the localized cusp magnetic field near the cathode surface and the electron density decreased rapidly as with the decrease in the magnetic field.