Diffusion of large-scale magnetic fields by reconnection in MHD turbulence

by Reinaldo Santos-Lima (University of Sao Paulo)

Tuesday 10 Nov 2020, 15:00 → 16:00 Europe/Stockholm

https://stockholmuniversity.zoom.us/j/940229961

https://ui.adsabs.harvard.edu/abs/2020arXiv200507775S/abstract

The rate of magnetic field diffusion plays an essential role in several astrophysical processes. It has been demonstrated that the omnipresent turbulence in astrophysical media induces fast magnetic reconnection, which consequently can lead to large-scale magnetic flux diffusion at a rate independent of the plasma microphysics. This process is called ``reconnection diffusion'' (RD) and allows for the diffusion of fields which are dynamically important. The current theory describing RD is based on incompressible magnetohydrodynamic (MHD) turbulence. We have tested quantitatively the predictions of the RD theory when magnetic forces are dominant in the turbulence dynamics. We employed the Pencil Code to perform simulations of forced MHD turbulence, extracting the values of the diffusion coefficient using the Test-Field method. Our results are consistent with the RD theory (diffusion proportional to the Alfvenic Mach number Ma to the power of 3 for Ma < 1) when turbulence approaches the incompressible limit (sonic Mach number Ms < 0.02), while for larger Ms the diffusion is faster (proportional to Ma to the power of 2). Our results generally support and expand the RD theory predictions.

SantosLima_10-Nov-2020.mp4