Design and Performance Simulation of Hot Cathode Pulsed Electron Gun

The collision ionization of high-speed directional rarefied gas beam by an electron beam requires the generation of ion beam within an extremely short time, so as to enable the collection of narrower ion pulse signals. A significant challenge arises from the inherent thermal response time of conventional hot cathodes, which can limit the temporal precision of electron emission. To overcome this limitation, this study designed and simulated a hot cathode pulsed electron gun capable of generating a high-current pulsed electron beam with specified energy. The key innovation involves pre-extracting a population of thermal electrons from the cathode surface, forming a readily available “electron cloud”. This approach enables nanosecond-scale pulsed electron beam control, effectively bypassing the delay associated with cathode heating and allowing for efficient ionization of rarefied gas molecules. The electron gun comprises several key components: a hot cathode, a reflector, an acceleration grid, a focusing electrode, and a grounded shielding cover. A compatible translational mechanism was designed, allowing for precise adjustment of the distance between the electron beam exit and the molecular beam during operation, thereby optimizing the ionization interaction region. Simulations were conducted using COMSOL Multiphysics software, incorporating the Particle Tracing Module to model electron dynamics under transient electric fields. The electrostatic field distribution and electron trajectories were analyzed in detail. Simulation results demonstrated that the hot cathode pulsed electron gun could generate a pulsed electron beam with an energy of approximately 70 eV within a pulse voltage period of 40 ns. The system exhibited excellent electron emission characteristics, with a simulated emission efficiency of 13.58% and a collection efficiency of 100% under the defined conditions. Furthermore, collision ionization simulations with N₂ gas yielded an ion production rate consistent with theoretical predictions, demonstrating an error of only 3.297%. These findings serve to validate the effective collision ionization performance of the electron gun and lay a valuable groundwork for future experimental verification and application.