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.

Carbon dioxide (CO2) and its mixtures are potential alternative gases for arc extinguishing in switchgear. During the arc decaying phase, the non-chemically equilibrium (non-CE) effect leads to the departure from the local thermal equilibrium (LTE) model in predicting the arc behavior. This work is focused on the dynamic behavior of CO2 arc during the current zero (CZ) period. A non-CE numerical model was established. The decay process of temperature, energy and electrical conductivity between the LTE and non-CE models were compared. The distributions of species compositions, non-equilibrium parameters together with the transport process of the particles were further investigated. The change of particle distributions caused by the non-CE effect is the main reason for the difference of temperature decay between non-CE and LTE. The particles transport at the edge of the arc depends on the radial convection and diffusion, while the transport of atoms in the arc core is the combined results of convection, diffusion and chemical kinetics. As a contrast, the transport of electrons and ions is still dominated by chemical reactions. The decay of electron density at the nozzle throat calculated by the non-CE model are in good agreement with the laser Thomson scattering (LTS) tests, while the LTE model failed to predict the electron density accurately, which proves that the non-CE effect of CO2 arc during CZ period cannot be ignored.