一种返回电子式的月表电场探测技术
doi: 10.11728/cjss2024.06.2024-0010 cstr: 32142.14.cjss.2024-0010
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金菲凡 女, 1999年8月出生于上海市, 现于中国科学院大学(中国科学院国家空间科学中心)攻读硕士学位, 主要研究方向为月球电场环境探测技术. E-mail: jffmtxjf@163.com -
刘超 男, 1981年3月出生于河南省周口市, 现为中国科学院国家空间科学中心正高级工程师, 博士生导师, 主要从事空间环境及等离子体就位探测技术的研究. E-mail: liuch@nssc.ac.cn
作者简介:
Return-type Electron-based Lunar Surface Electric Field Detection Technology
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摘要: 提出了一种原位探测月表电场的新技术及相应计算方法, 以满足探测南极月面电场环境特性的需求. 根据仿真结果, 月表电场精细测量需要低能散、高电流的平行电子束发射能力, 设计的低能层流电子枪在10–8～10–5 A的发射电流下, 能散<0.4 eV, 且随发射电流减弱而降低; 通过控制发射电流、调整阳极孔径, 可对电流进行调控; 采用pierce电子枪的阴阳极结构和静电透镜对电子束的平行度进行进一步控制, 仿真显示10–7 A电子束的扩散效果较弱, 各方面性能符合探测需求. 此外, 构建通过电子束返回时间测量垂直电场的探测方式, 模拟验证月表光照区向上发射电子束时相应的电场计算结果可反映背景电场, 返回电子式月表电场探测技术达到了执行月表电场测量所需的要求.Abstract: 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.
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图 1 电场中电位、电子束能量与返回位置的关系
Figure 1. Relationship between electric potential, energy of electron beam, and return position in the electric field
图 2 不同初始能量的电子在电场中的返回时间信号
Figure 2. Return time signals for electrons with different initial energies in the electric field
图 5 电子枪金属内部结构及对应电压设置
Figure 5. Internal metal structure of the electron gun and corresponding voltage settings
图 6 稳压阳极设为0 V (a) 脉冲模式下阳极调整为–100 V 电子(b) 的出射情况
Figure 6. Emission of electrons under regulated voltage with anode set to 0 V (a) pulse mode with anode set to –100 V (b)
图 9 电子枪表面施加50 V电位差时电子枪与月面的耦合鞘层电位分布
Figure 9. Potential distribution of the coupling sheath layer between the electron gun and lunar surface when a 50 V potential difference is applied to the electron gun surface
图 10 平整月表的高度空间电位分布
Figure 10. Spatial distribution of electric potential on a flat lunar surface
图 11 SPIS模拟的平整月表垂直电场结果
Figure 11. Vertical electric field of a flat lunar surface simulated by SPIS
图 12 类pierce结构理想情况下电子束的轨迹(从下至上分别为阴极、预聚焦极、阳极)
Figure 12. Trajectory of the electron beam in an idealized pierce-like structure (The components from bottom to top are the cathode, the pre-focusing electrode, and the anode respectively)
图 13 不同电流影响下空间电荷相互作用引起的能散
Figure 13. Energy spread caused by space charge interaction under different currents
图 14 1 mm阳极孔径下不同电流的空间电荷效应
Figure 14. Space charge effects under different currents with a 1 mm anode aperture
图 15 1000 K激发温度时不同孔径的电流通过情况
Figure 15. Current for different apertures at an excitation temperature of 1000 K
图 16 电子枪轴上电位分布以及电位梯度
Figure 16. Potential and potential gradient along the electron gun axis
图 17 理想情况下在2000 mm处汇聚的100 eV电子束受10–7A电流空间效应影响的模拟扩散结果
Figure 17. Simulated diffusion results of a 100 eV electron beam converged at 2000 mm in theoretical conditions under the influence of 10–7A current space charge effects
图 18 着陆器周围的电位分布及电场估计值. (a)水平方向, (b)垂直方向
Figure 18. Potential distribution and estimated electric field values in the horizontal (a) and vertical directions (b) around the lander
图 19 电子束运动轨迹 (绿色曲线为水平发射, 黑色曲线初始偏角为4°)
Figure 19. Trajectory of electron beam (Green curves represent horizontal emission, black curves represent the initial angle of 4°)
图 20 安装高度为0.3 m (a)和安装高度为1.6 m (b)情况下空间电位分布以及电子束返回情况
Figure 20. Potential distribution and electron beam return situation at an installation height of 0.3 m (a) and 1.6 m (b)
图 21 日侧和阴影区电子束发射方向及返回情况
Figure 21. Electron beam emission direction and return situation in the sunlit and shadowed regions
图 22 电子束受到的库仑力和洛伦兹力的比值
Figure 22. Ratio of Coulomb force to Lorentz force acting on the electron beam
图 23 施加不同电压差时空间各点电位与施加104 V时的差值
Figure 23. Potential difference at various points in space compared to a 104 V bias when applying different voltage bias
图 24 不同情况下Z=1.56 m处的空间电位 以及电子通过时间
Figure 24. Spatial potential and flight time of electrons at Z=1.56 m under different conditions
图 25 计算得到的空间中每伏的间距$ D $与背景场中对应值$ {D}_{r} $及两者的拟合关系
Figure 25. Calculated spacing $ D $ per volt and corresponding value $ {D}_{r} $ in the background field, as well as the fitting relationship between $D $ and ${D}_{r} $
表 1 性能参数
Table 1. Performance parameters
Potential range/
VElectric field range/
(V⋅m–1)Electric field resolution/
(V⋅m–1)(–100, +100) (0.5, 5) ≤0.5 
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