Estimation of Beam and Plasma Parameters for Electron Beam Transport in Ion-Focused Regime

摘要

This paper presents the analysis of cylindrical electron beam and beam-impact-generated plasma using particle-in-cell simulation code VSim 6.2 at different operating conditions. The transient plasma parameters, such as, beam density, charge neutralization factor, space charge potential, ionization time, beam compression, and plasma electron temperature, have been estimated and analyzed for a 40-keV, 10-100-A electron beam propagating in argon gas-filled drift space at different operating pressures. These parameters are difficult to be measured experimentally. The evaluated charge-neutralizing factor has been found dynamic in space and time, which is maximum at the beam envelope. The voltage profile of space charge potential required for effective electron beam propagation approaches zero due to formation of the plasma in the order of ionization time. The estimated average plasma electron temperature has been found to be less than ~1 eV, which is less damaging for interaction structure of the plasma-assisted microwave sources. It has been observed that an optimum pressure limit needs to be maintained inside the drift space to prevent the loss of electron beam due to instabilities resulting in excessive collisions with the drift space walls.