Comparison of ion velocity spectra of plasma bunches ejecting from the channels of nanosecond breakdown and vacuum surface flashover in KCl single crystals

Summary form only given. In our previous works [1, 3] we measured ion velocity spectra of a plasma bunch generated by vacuum flashover. In this work the parameters of plasma bunches ejecting from channels of nanosecond breakdown in KCl are measured. Comparison of parameters of plasma bunches generated by these different methods may advance our understanding of basic mechanisms of both processes. Experimental setup comprised nanosecond generator, vacuum chamber, and digital oscilloscope. The generator was a Tesla transformer built in coaxial forming line with gas-filled spark discharger. Pulses of voltage have amplitude of 140 kV under no load, pulse duration is 8 ns, rise times are less than 0.5 ns. Samples of crystalline KCl were put into a cell with needle anode and diaphragm-like cathode. Test cell was in the vacuum chamber and was connected to the generator. Faraday cup was used to measure current of ion component of plasma bunch. Permanent magnets near the cup effectively suppress the electron component of plasma bunch. Time-of-flight base varied from 10 to 50 cm. Velocities of the ions are derived from the measured delays of ion currents. The ions might be grouped as `fast´ (100 km/s) and `slow´ (30 km/s). The amplitudes These results let us conclude that bulk breakdown might serve as a source of dense non-ideal plasma as well as vacuum flashover. Earlier [2] a sequentially constricted breakdown channel which was as a result of an action of train of voltage pulses was observed in KCl. The ion spectrum of plasma ejecting from the sequentially constricted channel is also measured in this work.