Space current sheets: structure, stability and evolution

• Applicant: Professor Dr. Jörg Büchner
• Subject Area: Astrophysics and Astronomy
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426192610

In the hot and dilute collisionless plasmas of the Universe, current sheets (CSs) are the sites at which accumulated magnetic energy is released, often explosively, by reconnection, causing plasma heating, plasma-bulk-flow and particle acceleration. Hence, CSs are next to shock waves most important for the energization of astrophysical plasmas.Despite their relevance a number of crucial questions about structure, stability and evolution of astrophysical CSs are still unsolved. Among them are the influence of the ion composition, of anisotropies and the role of the plasma turbulence. The reason is that most astrophysical CSs are out-of reach for direct observations. Fortunately, cosmic CSs can be in-situ investigated in the heliosphere, e.g. in planetary magnetotails and in the solar wind. These investigations have revealed multi-scale CS structures due to ions heavier than protons, anisotropies in the particles velocity space distribution and turbulence down to the smallest, the electron scales.We plan systematical analysis of those properties of CS in three planetary magnetotails (Earth, Mars and Mercury) and in the solar wind, utilizing the wealth of existing satellite data from a unified point of view based on models of CS structure, stability and energy release through them, which we are going to develop, taking into account the abundance of ions, heavier than protons, anisotropic distribution functions and turbulence similar to the observed ones.Our comparative investigations take into account that, although the absolute parameters characterizing CSs in space plasmas considerably differ, the physically relevant quantities, normalized to the plasma conditions, indicate similar physical situations. For this purpose we will utilize multi-spacecraft observations in the Earth's magnetotail by CLUSTER at ion scales and by MMS at electron scales. For the investigations of CSs in the Martian magnetotail we will use MAVEN observations, for the Hermean magnetotail those of MESSENGER, for CSs in the solar wind the heliospheric spacecraft STEREO A and B, WIND, ACE, ULYSSES, HELIOS 1 and 2, CASSINI, VOYAGER 1 and 2. We will develop and apply analytical models of CS structure in dependence on the observed environmental conditions, investigate their stability theoretically and by means of numerical simulations, explore the nonlinear consequences of the evolution of the unstable structures as well as of reconnection through them utilizing test-particle, hybrid-kinetic and PIC-code numerical simulations. We will verify the model predictions of multi-scale CS structures and their evolution under the influence of heavy ions, anisotropic distribution functions and turbulence by means of space observations, as well as the spectra of energetic particles, in order to be able to draw conclusions also for remote astrophysical CSs, not directly accessible for in situ observations.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Science Foundation, until 3/2022
• Co-Investigator: Professor Dr. Dieter Breitschwerdt
• Cooperation Partner: Professor Dr. Lev Zelenyi, until 3/2022