Space-charge modulation in vacuum microdiodes at THz frequencies

TL;DR

This paper explores the behavior of electron beams in microscopic vacuum diodes, revealing space-charge effects and THz frequency electron bunching through high-resolution molecular dynamics simulations.

Contribution

It provides detailed simulations of space-charge effects in microdiodes and demonstrates THz electron bunching with an analytical explanation.

Findings

Breakup of single electron pulse beyond Child-Langmuir limit

Formation of electron bunch train at THz frequencies

Analytical model explaining bunching behavior

Abstract

We investigate the dynamics of a space-charge limited, photoinjected, electron beam in a microscopic vacuum diode. Due to the small nature of the system it is possible to conduct high-resolution simulations where the number of simulated particles is equal to the number of electrons within the system. In a series of simulations of molecular dynamics type, where electrons are treated as point-charges, we address and analyze space-charge effects in a $\mu$m-scale vacuum diode. We have been able to reproduce breakup of a single pulse injected with a current density beyond the Child-Langmuir limit, and we find that continuous injection of current into the diode gap results in a well defined train of electron bunches corresponding to THz frequency. A simple analytical explanation of this behavior is given.