Scaling of Magnetic Dissipation and Particle Acceleration in ABC Fields

by Qiang Chen (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw)

Tuesday 30 Mar 2021, 15:00 → 16:00 Europe/Stockholm

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

Using particle-in-cell (PIC) numerical simulations with electron-positron pair plasma, we study how the efficiencies of magnetic dissipation and particle acceleration scale with the initial coherence length λ0 in relation to the system size L of the two-dimensional (2D) `Arnold-Beltrami-Childress' (ABC) magnetic field configurations. Topological constraints on the distribution of magnetic helicity in 2D systems, identified earlier in relativistic force-free (FF) simulations, that prevent the high-(L/λ0) configurations from reaching the Taylor state, limit the magnetic dissipation efficiency to about ϵdiss≃60%. We find that the peak growth time scale of the electric energy τE,peak scales with the characteristic value of initial Alfven velocity βA,ini like τE,peak∝(λ0/L)β−3A,ini. The particle energy change is decomposed into non-thermal and thermal parts, with non-thermal energy gain dominant only for high initial magnetisation. The most robust description of the non-thermal high-energy part of the particle distribution is that the power-law index is a linear function of the initial magnetic energy fraction.

https://arxiv.org/abs/2102.09303

 

 

Chen_30-Mar-2021.mp4