On the Mechanism of Picosecond Electron Beam Generation in Gas-Filled Diode with Cold Cathode

Summary form only given. Experimental facts confirming the emissive mechanism of picosecond electron beam formation in gas-filled diode with a non-uniform distribution of potential in the accelerating gap are given in the report. Gas ionization near the cathode leads to its screening and it is the most probable reason for the limitation of beam current duration. Voltage pulses with an amplitude of up to -250 kV (in the traveling wave), rise time and pulse duration (FWHM) from 100-150 ps were applied to the diode cold cathode. Electric fields on the edge of cathode could reach 1-2 MV/cm and more. We assume that generation mechanism of electron beam with a duration less than 60 ps and currents in the units of amperes is the regime of the continuous acceleration (running away) of electrons emitted by cathode in an early stage of the transition from field emission (FE) to explosive electron emission (EEE), or even before the onset of this transition. This is obvious because the process of beam generation and its "switch off" completes much earlier than the maximum of electron beam current is reached with the evacuation of the same diode gap. In the latter case, the beam current occurs 1-2 orders higher. The dependence of beam current amplitude on the duration of low-voltage prepulse also shows the significant role of cathode FE processes on the injection of running away electrons in the diode with gas isolation. Furthermore, the higher beam current in the identical geometry is available for the cathode material with the lowered work function and the increased delay time of EEE. In this case, with the fixed rate of voltage rise on the cathode it is possible to reach large electric fields, which facilitate the conditions for the gap passing by running away electrons possessing an increased energy. With the greatest resolution of real-time oscilloscopic registration accessible to date we intend to obtain the data on the correlation of electron beam current duration and the- value of accelerating gap. As well as to see the relationship of the moments of running away electrons generation and overlap of the accelerating gap by gas discharge.