First investigation of the diamagnetic cavity boundary layer with a 1D3V PIC simulation

Beth, A., Gunell, H., Simon Wedlund, C., Goetz, Charlotte, Nilsson, H. and Hamrin, M. (2022) First investigation of the diamagnetic cavity boundary layer with a 1D3V PIC simulation. Astronomy & Astrophysics, 667. A143. ISSN 0004-6361

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Context. Amongst the different features and boundaries encountered around comets, one remains of particular interest to the plasma community: The diamagnetic cavity. Crossed for the first time at 1P/Halley during the Giotto flyby in 1986 and later met more than 700 times by the ESA Rosetta spacecraft around Comet 67P/Churyumov-Gerasimenko, this region, almost free of any magnetic field, surrounds nuclei of active comets. However, previous observations and modelling of this part of the coma have not yet provided a definitive answer as to the origin of such a cavity and on its border, the diamagnetic cavity boundary layer. Aims. We investigate which forces and equilibrium might be at play and balance the magnetic pressure at this boundary down to the spatial and temporal scales of the electrons in the 1D collisionless case. In addition, we scrutinise assumptions made in magneto-hydrodynamic and hybrid simulations of this environment and check for their validity. Methods. We simulated this region at the electron scale by means of 1D3V particle-in-cell simulations and SMILEI code. Results. Across this layer, depending on the magnetic field strength, the electric field is governed by different equilibria, with a thin double-layer forming ahead. In addition, we show that the electron distribution function departs from Maxwellian and/or gyrotropic distributions and that electrons do not behave adiabatically. We demonstrate the need to investigate this region at the electron scale in depth with fully kinetic simulations.

Item Type: Article
Additional Information: Funding Information: We warmly thank the referee for his/her positive comments and promptitude. Work at Umeå University was supported by the Swedish National Space Agency (SNSA) grant 108/18. CSW thanks the Austrian Science Fund (FWF) P32035-N36. The authors would like to acknowledge ISSI for the opportunity it offered for very valuable discussions on this topic as part of the International Team 499 “Similarities and Differences in the Plasma at Comets and Mars”. The simulations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at the High Performance Computing Center North (HPC2N) at Umeå University in Sweden. The colour scale used in Figs. 2–4, 5, 10, and 11 which is colour-blind friendly has been generated with the MATLAB code provided by Matthias Geissbuehler (see Geissbuehler & Lasser 2013).
Uncontrolled Keywords: Comets: general, Magnetic fields, Plasmas
Subjects: F300 Physics
F400 Forensic and Archaeological Science
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Rachel Branson
Date Deposited: 22 Feb 2023 14:43
Last Modified: 22 Feb 2023 14:45

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