Plasma-driven temporal collimation of sheet electron beam

Abstract

Collimating high-current-density sheet electron beams using external magnetic fields presents significant challenges, particularly due to complications such as diocotron instability. To address these issues, we introduce a non-magnetic, plasma-assisted planar collimator in this Letter. In this study, a plasma-assisted planar collimator was developed, and its performance was analyzed by utilizing a pulsed electron beam source to propagate a transient sheet electron beam through it for 50 ns duration. A collimated beam of dimensions 7.1 mm × 0.75 mm was captured near the collimating region, exhibiting notable compression along the beam height compared to its width. This uneven compression highlights the need for a detailed understanding of particle dynamics within the collimator. However, experimental diagnostics using traditional probes inside a planar collimator are constrained due to spatial limitations. To overcome this, a 3D Particle-In-Cell simulation study was conducted using VSim Multiphysics to model the interaction of the electron beam with neutral gas, resulting in impact ionization within the collimator. The simulation results reveal the role of the temporal and spatial ionization profiles that drive beam compression and shaping. A good correlation of compression factor between experimental and simulated results was observed, with the simulated beam size measuring 6.75 mm × 0.65 mm. This work offers valuable insights into the design of collimators for high-current-density sheet electron beams, with applications in high-power, compact microwave and THz sources.