Scaling of Magnetic Dissipation and Particle Acceleration in ABC Fields

Qiang Chen; Krzysztof Nalewajko; Bhupendra Mishra

doi:10.1017/S0022377821000209

paper

Scaling of Magnetic Dissipation and Particle Acceleration in ABC Fields

arXiv:2102.09303 · doi:10.1017/S0022377821000209

Abstract

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 $λ_{0}$ 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- $(L / λ_{0})$ configurations from reaching the Taylor state, limit the magnetic dissipation efficiency to about $ε_{diss} ≃ 60%$ . We find that the peak growth time scale of the electric energy $τ_{E, peak}$ scales with the characteristic value of initial Alfven velocity $β_{A, ini}$ like $τ_{E, peak} \propto (λ_{0} / L) β_{A, ini}^{- 3}$ . 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.

arXiv commentPublished in Journal of Plasma Physics, 17 pages, 7 figures, 1 table

Scaling of Magnetic Dissipation and Particle Acceleration in ABC Fields

Abstract

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