Cathode plasma electron temperature measurements in REB diodes

In recent experiments with parallel plate REB diodes, no difference in cathode plasma gap closure velocity, as inferred from the impedance behavior, was observed over a range of current densities form 4.35kA/cm/sup -2/. If the expansion is of a thermal nature, this would imply that the electron temperature depends weakly on current density over this range. Alternatively, the increased heating at higher current densities may be balanced by retardation of the plasma due to the higher self-magnetic field. On the other hand, directed flows of ions from cathode spots have been observed in vacuum arcs, implying that there may be a nonthermal component to cathode plasma expansion. The authors, have observed similar phenomena in diode plasmas, where all species (A iota,C,H) are observed to expand at roughly the same rate. To gain more insight into the physics of cathode plasma expansion, measurements of the electron temperature, based on line rations, are presently being carried out. Measurements are presented for different current densities and cathode materials, and at different distances from the cathode surface