2025/02/03 by Park, Kiwan
#FOS: Physical sciences #Plasma Physics (physics.plasm-ph) #Solar and Stellar Astrophysics (astro-ph.SR) #Space Physics (physics.space-ph)
paper · doi:10.48550/arxiv.2502.01300
We investigated the α and β effects in a rotating spherical plasma system relevant to astrophysical environments. These coefficients were derived using three different approaches based on the large-scale magnetic field B, turbulent velocity u, and turbulent magnetic field b, yielding αEM-HM, βEM-HM, βvv-vw, and βbb+jb. Using raw data from direct numerical simulations (DNS), we constructed the magnetic induction equation incorporating the α and β coefficients. We then reproduced the B field and compared the results with the DNS data. In the kinematic regime, where B is weak, all models exhibit good agreement with the DNS results. However, in the nonlinear regime, the B field, reproduced using βvv-vw, deviates from the DNS and exhibits unbounded growth. To address this discrepancy, we added βbb+jb, which represents the contribution of turbulent magnetic fields, to βvv-vw. This addition suppresses the divergent growth of B in the nonlinear regime. We then assessed the actual influence of α and β on the evolution of B by applying weighted combinations of the two coefficients. Our results show that magnetic β diffusion plays a dominant role throughout the entire process. In contrast, the α effect is minor in the kinematic regime but becomes essential for sustaining the B field in the nonlinear regime. We also discussed the underlying physical mechanism responsible for this behavior.