Experimental and theoretical investigations of the conditions for the generation of runaway electrons in a gas diode with a strongly nonuniform electric field

Abstract

The conditions under which runaway electrons are generated in a gas diode with a strongly nonuniform electric field created by electrodes of specific geometry have been investigated. For an edge cathode, the equation of motion for electrons has been solved analytically. According to the solutions, for electrons to run away at the periphery, in the low field region, it is necessary that the applied potential difference be greater than a certain threshold determined by the electrode gap spacing and by the parameters of the gas. This condition supplements the classical electron runaway condition according to which the field strength near the emitting edge of the cathode should exceed some value depending only on gas parameters. It turned out that for a sharp-edged cathode, the new condition imposes more stringent requirements on the field strength compared with the classical one. Our calculations are supported by experiments in which electron runaway conditions were determined for a set of cathodes with different edge radii.

Generation of runaway electrons in plasma after a breakdown of a gap with a sharply non-uniform electric field strength distribution

“…They can be used are also generated in tokamak-type setups, including ITER, and damage the internal components of the vacuum chamber [8][9][10][11]. In nanosecond gas discharges, REs are often generated in the prebreakdown stage [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. They can be measured directly with a collector or by measuring x-ray radiation [29][30][31][32][33][34].…”

Emission Features and Structure of an Electron Beam versus Gas Pressure and Magnetic Field in a Cold-Cathode Coaxial Diode

“…In addition, for the vacuum approximation, one can calculate dynamic impedance Z(t) of the MICD and the current in the load (i.e., current of the beam or discharge) I L (t): Formation of a picosecond RAE flow in a gas begins at the leading edge of the voltage pulse U 1 (t), when a critical electric field E cr is achieved near the cathode edge (at the boundary of plasma formations near FE centers), which is sufficient for thermal electrons to run away [47]. As a result, for the passage of RAEs to the anode constriction, special criteria are fulfilled in our case [59]. As seen in Figure 3b, the smaller the MICD gap D, the smaller the (modulo) amplitude of a non-inverted part of the pulse U ref (t).…”

The polarity effect of nanosecond voltage pulses on the propagation of streamers in a point-to-plane gap filled with air

“…The subnanosecond breakdown [23][24][25] of a point-to-plane gaps, which occurs at high overvoltages, has some features. With a negative pointed electrode, runaway electrons (REs) affect the formation of a negative streamer due to preliminary ionization of the gas.…”