Return-type Electron-based Lunar Surface Electric Field Detection Technology

This study aims to propose an active, on-site, high-resolution lunar surface electric field detection technology along with corresponding computational methods, to meet the requirements of exploring the comprehensive characteristics of the lunar surface environment, and helps understanding the interaction between the Moon and solar wind. According to the simulation results, precise measurement of lunar surface electric fields demands electron emission capabilities with low energy spread, relatively high current, and parallel electron beams. Preliminary system parameters with the capability of receiving return current signals have been designed, including system parameters for voltage stabilization, pulse power supply modules, and signal acquisition modules. Referring to the simulation results, the low-energy laminar flow electron gun designed in this study exhibits an energy spread of <0.4 eV at emission currents ranging from 10^–8 to 10^–5 A, with the energy spread decreasing as the emission current weakens. Control of emission current is achieved by regulating the initial current of the thermionic cathode, employing a cathode-anode structure like Pierce electron gun and adjusting the anode aperture. Additional control over beam parallelism is achieved using an electrostatic lens. Simulation verifies that the 10^–7 A electron beam exhibits minimal diffusion within a 4 m working distance, meeting the requirements for accurate detection of lunar surface electric fields. The paper proposes and simulates the measurement of lunar electric fields by emitting electron beams upwards in the lunar illuminated region. The simulation and calculation results of lunar vertical electric fields show a linear relationship, verifying the feasibility of the detection plan, with the influence of background magnetic fields being negligible. The feasibility of actively adjusting the electron gun reference potential to expand the electron beam range to (–100, +100) V has also been proposed and verified. According to simulation analysis, our return-type electron-based lunar surface electric field detection technology, along with the designed and manufactured low-energy electron gun, can meet the requirements for mobile, non-contact detection of vertical electric fields on the surface of the lunar South Pole.