Beam-assisted extraction of charged particles from a decaying plasma

In this paper, a novel method is proposed to enhance ion extraction flux from collision-free decaying plasma by injecting an energetic electron beam from the cathode surface. A numerical model accounting for initial plasma generation and relevant plasma-wall interactions is established and implemented into an electrostatic particle-in-cell code. The model and the numerical code are validated by comparing the results obtained without beam injection against known experimental scaling for the extraction process. Based on this validation, simulations with an externally injected electron beam are conducted. Our results show a significant enhancement of the ion extraction flux, as well as a corresponding reduction of the ion extraction time, e.g. by a factor of 3 when the beam current is set at 600 A m⁻². The analysis of spatiotemporal evolution of the electric potential during the plasma expansion process shows the formation of a standing Langmuir wave, excited by the beam, in the bulk plasma. Interaction of this wave with the bulk electrons provides an efficient heating mechanism. Higher mean energy of plasma electrons leads to higher ion-acoustic speed, and thus, results in the enhancement of the ion extraction flux. (paper)