Contributed Talk - Splinter Magnetic

Thursday, 24 September 2020, 14:25   (virtual room H)

Radioastronomical diagnostics of magnetic reconnection via electron velocity distribution function

Xin Yao, Patricio A. Muñoz, and Jörg Büchner
1. MPI for Solar System Research, Göttingen. 2. ZAA, TU Berlin, Berlin.

Magnetic reconnection takes place, perhaps, in many astrophysical plasmas where it converts magnetic energy, e.g., to plasma heating and acceleration of charged particles to high energies. In contrast to reconnection experiments in the laboratory and its in-situ - observation in space plasmas astrophysical reconnection can be detected only remotely, e.g. by its radio-emissions. Radio-emission from solar flares can be used as a test-ground for other cases of astrophysical reconnection processes. It is conjectured that flare-related radio bursts are caused by energetic electrons beams accelerated by reconnection. A self-consistent description of electron beam distributions requires a kinetic approach and numerical simulations. We carried out 3D fully kinetic particle-in-cell (PIC) code simulations of magnetic reconnection using the ACRONYM code. Our goal is to characterize the possible sources of free energy of the generated distributions functions in dependence on the background magnetic field strength. Those distribution functions can be prone to different micro-instabilities and thus to cause radio-emission. We found that (1) In the limit of strong background magnetic fields electron beams with positive gradient in the parallel (to the local magnetic field direction) velocity space direction are formed by magnetic reconnection. They can generate plasma emissions via wave-wave interactions. (2) In the case of weak background magnetic fields additionally positive gradients in the perpendicular velocity space direction are formed. Those can generate electron cyclotron maser radio emission as a result of a direct wave-particle interaction.