9:00 AM - 10:30 AM
[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
Long-period comets have orbital periods longer than 200 years. These comets are believed to preserve pristine features of the solar system and are attracting considerable attention as they can contribute to the elucidation of the formation process of the solar system. The Comet Interceptor was selected by ESA as a new fast-class mission, in which three spacecraft will discover, visit, and explore a pristine comet. Comets consist of an icy nucleus and a surrounding cloud of gases called coma, the latter of which are molecules liberated from the nucleus by solar heating and sublimation. Some of the ice composing the coma is ionized and forms a cloud of dense plasma. The cometary dense plasma is considered to have unique properties due to its sharp density gradient, interactions with the solar wind, and mixing with dust. It is important to study the physical processes occurring there in detail prior to the exploration.
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).
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).