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[PEM17-P03] Particle simulations of perturbation processes at the surface of high-density cometary plasmas
Keywords:High-density cometary plasma, Density perturbation, Particle simulation, Ambipolar electric field
This study is focused on density perturbations emerging in the surface region of the cometary high-density plasma. We performed electrostatic plasma PIC simulations to reproduce their detailed processes. In the simulations, a high-density plasma was initially placed in a part of the computational space, while the rest of the space was set as a region of vacuum. A static magnetic field was applied throughout the computational space. The simulations exhibited the significant changes in the plasma density structure and the development of the electrostatic field. The outlines of the obtained results are as follows. At the initial stage of the simulation, electrons and ions try to expand from the high-density region to the low-density side. Because electrons are more strongly magnetized than ions, the ions are more likely to expand outward than the electrons. This results in the formation of a bipolar electric field oriented inward in the radial direction. Subsequently, a density disturbance of electrons and ions develops in the direction along the boundary of the initial high-density plasma, creating a vortex-like density and potential structure. Based on the above results, we have made a parametric study by changing the structure of the initial plasma configuration, the ion-to-electron mass ratio, and the magnetic field strength. It was confirmed that the identified perturbations have the characteristics of the lower hybrid drift instabilities (LHDI).