| The Moon is a typical object without an atmosphere and without a global magnetic field.The lunar surface sample is a non-conductor material.The lunar surface in solar extreme ultraviolet radiation and space plasma will have a charging and discharging effect.The lunar surface potential has an important impact on lunar scientific exploration and the safety of instruments.Aiming at the support needs of China manned moon landing program,we carry out movable non-contact potential detection technology experiments,which can provide accurate and quantitative lunar surface potential data.By emitting electron beams with controllable energy to the lunar surface,the surface potential can be obtained according to the presence or absence of reflected electron beams.In this paper,a low-energy far-focus electron gun is studied,which can achieve precise control of electron beam emission in a wide energy range and accurate collection of reflected electron beams.The main work of this paper includes:(1)This paper fully investigates the space environment of the moon.And according to the performance indicators of the lunar potential probe,the functional requirements of the low-energy far-focus electron gun is determined.Then design the electron beam optical path diagram for measuring the lunar surface potential.(2)According to the principles of the electron gun,the low-energy tele-focus electron gun and the electron beam deflection system is designed.The electron gun,electron beam deflection system and current collector are then assembled into a non-contact measurement probe.The probe weight is about 1kg.(3)Using SIMION to simulate and verify the low-energy tele-focus electron gun.The result shows that the proportion of the reflected electrons received by the collector is above 65%,and the highest proportion is between 88% and 96%.Then the electron beam deflection system is simulated.The result indicates that the usable deflection angle of the deflection system is about ±16.56°,and it adapts to the lunar rover tilt angle of ±33.12°.(4)Finally,the electron gun prototype is tested.The test result indicates that the adjustable length between beam waist and the exit of electron gun is about 168 mm to183mm.The beam current at 500 mm has no attenuation compared with other positions,so the electron gun could work at long-distance.And the energy of electron beam is between 50 e V and 500 e V,the design target of 2e V to 500 e V has not been fully achieved.The relative error of energy is within 10%,which is related to the energy.The lower the beam energy,the greater the error.Finally,the non-contact potential measurement results of the simulated lunar surface show that when the geomagnetic shield is not turned on,the minimum energy of the electron gun is 130 e V,and the relative error of the potential measurement results is less than 6%.It can be concluded that the low-energy far-focus electron gun designed in this paper can meet the requirements of the movable non-contact lunar surface potential detector. |
