Highly ionized helium arc plasma. Determination of the temperature in nonequilibrium conditions and the effect of plasma microfields

Methods are proposed for the spectral measurement of electron temperature $T_e$ in a highly ionized nonequilibrium He plasma at atmospheric pressure based on a comparison of the intensities of atomic and ionic lines with a whole complex of experimental data (primarily, $n_e$). The large energy gap between the emitting $\rm HeI$ and $\rm HeII$ excited levels (of more than $50$ eV) and allowance for the nonequilibrium manifested in the overpopulation of the atomic levels with respect to the ionic levels make it possible to make reliable and simple $T_e$ estimates, especially if the ionization energies of the emitting levels of the atom and the ion are close. For practical use, three pairs of $\rm HeI$ and $\rm HeII$ lines observed in the spectral range of $200$–$1100$ nm are recommended. The radial and temporal (upon the quasistationary pulsed heating of the electric arc plasma) dependences of $T_e$ are obtained in the range of axial values of $3.2$–$4.7$ eV.