Electron temperature and heating processes in a dynamic plasma of a high-power diode

Using time-dependent measurements and calculations of line-intensity ratios, we have determined the electron temperature of a surface flashover anode plasma in an intense ion diode to be 5--8 eV. The electron temperature was determined independently from C iii, Mg ii, and Al iii line intensities. The calculations accounted for the continuous particle flow from the anode surface into the plasma using the measured electron density. Furthermore, the electron-temperature gradient in the plasma was observed and found to be <1 eV/mm. The assumption that the plasma conductivity is classical, resulting in the electron heating being dominated by the currents induced in the plasma by the electron flow in the diode gap, was found to be in clear disagreement with the observed temperature gradient. The use of an anomalous plasma conductivity that is {}10×{} lower than the classical conductivity, which was previously suggested based on the magnetic field penetration into the plasma and the plasma expansion against the magnetic field, yields electron heating dominated by the pressure-driven current in the plasma. This can explain the electron heating and the electron-temperature gradient observed.