Plasma characterization in a diode with a carbon-fiber cathode

Results of optical and spectroscopic studies of the plasma formation at the surface of two types of carbon-fiber cathodes in a diode powered by an similar to 200 kV accelerating pulse are presented. It was found that during the pulse, generation of the plasma occurs in a form of several millimeter size plasma spots. In the vicinity of the cathode surface the average plasma density and temperature were found to be similar to 3 x 10(14) cm(-3) and similar to 5 eV, respectively, for an electron current density of similar to 22 A/cm(2). The plasma expansion velocity toward the anode was found to be similar to 1.5 x 10(6) cm/s during the first 150 ns of the accelerating pulse duration. (C) 2008 American Institute of Physics.