Beam discharge excited by distributed virtual cathode

Abstract

A new type of beam discharge, i.e., beam discharge with a distributed virtual cathode (VC) is pro posed and considered by numerical simulation. The discharge is established during counter motion of high current electron beams in a gas filled equipotential cavity and is characterized by a state of hot dense electron plasma of primary electrons. The discharge temporal dynamics is studied. It is shown that the VC lifetime depends linearly from this sum in a wide range of the sum of beam currents, from the boundary current of two beam instability to the critical current of Pierce instability. Generation of nonlinear electrostatic struc tures shaped as phase bubbles in the discharge is detected, and their dynamics is studied. The parameters are determined, at which the multiple coexistence of phase bubbles and their coalescence during collisions is observed.

Particle‐in‐cell/Monte Carlo‐simulation of the discharge in helium initiated by a relativistic electron beam in the chamber with a magnetic mirror

“…Such phase holes were observed at the simulation of discharges on the relativistic beams with a VC. [ 47,48 ]…”

“…The gas ionization was calculated by the Monte Carlo method (MC method). Only elastic collisions of electrons with gas atoms and ionization processes by electron impact were considered (Figure 2; ionization threshold is 24.6 eV [ 47 ] ). We used numerical data from ref.…”

“…The code was used many times to simulate beam [31,32,34,37,39,[42][43][44]49,59] and gas-discharge processes. [20,47,48] .…”

“…Such phase holes were observed at the simulation of discharges on the relativistic beams with a VC. [47,48] F I G U R E 10 Evolution of the phase portrait of the helium plasma from 25 to 250 ns with the step of 25 ns (inactive ions He + in red)…”

“…It was proposed before to use the squeezed state of relativistic electron beams for gas ionization to form an extended discharge channel. [ 47 ] So, a discharge is studied numerically in ref. [48]; it is initiated by a prelimit relativistic electron beam, which after having passed the gas chamber is directed again into it by means of a special electrostatic reflector.…”