Theory of the initial stage of low pressure arc discharge with thermionic cathode

Abstract

Constant attention and imterest invoked by the low-pressure discharge with current provided by the thermal emission of the hot cathode axe due to its wide application in electron engineering. Investigations of physical processes involved in the initial stage of the Knudsen discharge are necessary for aims of producting auxiliary discharges in the Knudsen mode of Cs-Ba-filled TEC,using a pulse discharge in TRICE-reactor /1/ and developing of invertors converting DC into AC. Depeudences of discharge ignition voltage and discharge development time on various factors axe of practical interest. It is important, too, to study diode perveance i.e. diode current-passing capability i n the presence of ions in pre-discharge modes.Current rise at the hitial stage of the Knudsen discharge is due to two main processes: direct impact ionisation of gas atoms by electrons accelerated by the electric field in the interelectrode gap to energies exeeding the ionization potential and compensation of the electron space charge limiting the passing current by ions. Under certain conditiom some accompanying elementary processes (collisions of charged particles with gas atoms,reflection of charged particles from electrode surfaces, etc.) may be essestial,too.Sn this report a quantitative kinetic theory of the initial stage of Knudsen discharge development is proposed which allows to relate macroscopic characteristics with elementary processes cross sections. A quantitative description of the initial discharge stage at low pressures requires solving of a system of kinetic equations for the charge particle distribution function t a k i n g i n t o account volume ion generation and the Poisson equation for the self-consistent electric field potential in the gap. Effective numerical-analytical methods have bees developed for solving these equations under steady-state conditions as well as for calculating a transient process at impulse voltage application between electrodes.In the steady-state case /2,3/ the distributions of electron and ion densities at given potential distribution @(Zlin t-he gap and current passing through the diode,&, are determined analytically from the conservation laws for the flow and the energy of particles. Usina the Poisson eauation we obtain a nonli-TIF=O=O 9 ?I =\=.rZ4 i Heref = Z / d -distance from the cathode i n units o the electrode se ara i o n d ,? =@/@i,

High-Power Subnanosecond Beams of Runaway Electrons Generated in Dense Gases

“…Total cross-sections of an electron -a nitrogen molecule collision were collected from [43][44][45][46][47] and cross sections of nitrogen molecule ionization from [48][49][50][51]. The excitation of the 10 lowest electronic states (data of [52,53]) and the 8 lowest vibration levels ( [54,55]) of a nitrogen molecule were accounted (Fig. 5).…”