Space Charge Effects on Short-Pulse Beam Dynamics in Vacuum Diodes

Space charge effects present significant challenges to the advancement of electron beam-based technologies, including high-power vacuum devices and ultrafast atomic resolution electron imaging [Zhang et al., Applied Physics Reviews 4, 011304, 2017]. The Child-Langmuir law sets a threshold for continuous electron beams in vacuum diodes. However, recent theoretical and experimental findings suggest that this limit can be exceeded when dealing with electron pulses of short durations compared to the electron transit time across the gap [Valfells et al., Physics of Plasmas 9(5), 2377-2382, 2002].

We focus on investigating the influence of space charge effects on the dynamics of square-top and Gaussian short-pulse beam profiles using a 1D multiple-sheet model. We consider various factors that contribute to the overall dynamics, including initial profiles, charge densities, pulse widths, and gap potential and distance. Specifically, we pay attention to the current density limit as the pulse length decreases and the beam's distortion as it traverses the gap. Our study involves a detailed analysis of electron sheets phase-space trajectories within the vacuum gap, examining the evolution of pulse profiles during transit. We also investigate the temporal changes in the electric field, potential within the diode. By assessing the distortion of short-pulses with varying charge density and diode parameters, our research offers further insights into the impact of space charge effects on overall beam dynamics