| The lunar regolith environment of lunar surface put forward a severe challenge onthe reliability of the spacecraft and other related instruments. In the lunar dustenvironment, the charged dust is levitated in the air, which has a great influence on thespacecraft. It is significant to research the lunar surface electric field.In this paper, we establish a mathematical model of photoelectron sheath andplasma sheath to compute their electric potential distribution and simulate the sheath onlunar surface with numerical simulation program based on PIC. Potential distribution,each particle density distribution and the overall charge density distribution wereobtained by calculating numerical and analytical models. The solutions of the twomodels are very close and both consistent with the observed data. The factors affectingthe accuracy of numerical simulation program were analyzed and the numericalsimulation program was conducted a preliminary optimization. How sheath convertfrom one type to another type and factors influencing the sheath oscillation wereexplored. How solar wind velocity, density of photoelectron and beam angle affect thesheath on the lunar surface was also researched.The results show that the numerical simulation program based on PIC method, cansimulate the sheath on the lunar surface well, and the results obtained were within therange of observed data. When the solar wind velocity is large enough and the placeclose to the subsolar point, the sheath is in the state of oscillation and the frequency ofthe oscillation and plasma is in the same order of magnitude. We found that the potentialand the sheath electric field energy vary continuously in the transition region. With thebeam angle increasing, the sheath transform from classical sheath to photoelectronsheath, and then transform from photoelectron sheath to oscillation sheath. The solarwind velocity, photoelectron density, and the beam angle have a significant effect on thesheath on the lunar surface. |
