Simulations of the Self-Focused Pseudospark-Sourced Electron Beam in a Background Ion Channel

Abstract

Using pseudospark discharge sourced electron beams for the generation of high-peak-power millimeter and terahertz radiation attracts increasing research interest in recent years. However, one of the crucially important and hitherto unanswered questions is "what is the upper-frequency limit at which millimeter-wave devices can be driven by pseudospark discharge sourced electron beams?". In this paper, we studied this question from the perspective of beam transportation in a plasma background, more specifically an ion channel using particle-in-cell simulations to find the limitations. The parameter ranges of the beam transportation with small oscillations in the beam diameter were investigated and summarized, through simulations of beam propagation in a large diameter drift tube with different ion densities, plasma electron densities, beam density distributions, and beam energies. The beam transportation in a small diameter beam tunnel was also simulated. It showed the maximum beam current with a small velocity spread that can be transported in the beam tunnel was determined by the diameter of the beam tunnel and the ion density. High injected current will cause significant beam loss and reduce the overall efficiency. The simulation results indicate a minimum diameter of the beam tunnel in a millimeter-wave circuit that can be effectively driven by a pseudospark-sourced electron beam. The equivalent upper limit in the operating frequency is about 400 GHz.

Investigations on enhanced plasma expansion in pseudospark discharge assisted by a magnetic switch

“…Compared to the simulation results without the MS discussed in the literature [37][38][39][40][41], the plasma expansion in figure 11 with the MS is much more notable. The main reason is that the existence of the MS prolongs the duration of lowcurrent and low-voltage stages, which gives more time for the electrons and ions to fully participate in collisions before the plasma density reaches the critical value that can induce the formation of macroscopic cathode spots.…”

“…Due to the cylindrical and symmetrical structure of the cathode cavity, electrons move in the pendulum motion and significantly increase the probability of collision ionizations in the hollow cathode, and thus the hollow cathode effect starts to play a dominant role in the multiplication of charged particles. Details of the initial phases of the pseudospark discharge can be found in a series of literature [37][38][39][40][41]. As time goes by, the electron density in the discharge region keeps increasing as shown in figures 11(a-iii) and (a-iv), and the peak values of electron density always locate in the cathode hole region.…”

Simulation of pseudospark discharge and the transportation of the generated electron beam

“…The simulated model is shown in Fig. 4 [10]. Different plasma densities and beam energies were simulated to study the conditions for stable beam transportation.…”