Magnetic Fields Generation Over Macroscopic and Cosmic Scale Distance

The important problem of generating significant magnetic fields in plasmas, of relevance to space and astrophysics and involving macroscopic scale distances is dealt with. For this, the requirements of processes depending on transitions over “microscopic” scale distances (e.g. ≤ c / ω_pe ) or on the Weibel instability are considered as excessively severe. Instead, a “cosmic alternator” process [1], involving extremely low frequency density fluctuations and a significant unperturbed electron temperature gradient, is introduced in order to create a “seed” sheared magnetic field. These fluctuations are considered to be driven, for instance, by the kinetic energy of the components of a binary system (e.g. with black holes) immersed in a circumbinary disk. In the presence of significant spatial gradients of anisotropic electron temperatures [2], in the produced quasi-steady state, an oscillatory magnetic reconnection process [1] can be sustained that involves macroscopic and mesoscopic [1] scale distances (a.k.a. magneto-thermal reconnection). Then the amplitude of the reconnected configuration can grow to significant amplitudes when a plasma density gradient, is present and combined with the temperature anisotropy. A growth rate is found that depends on finite particle transport [2] transverse to the (quasi equilibrium) magnetic field.

1. B. Coppi and B. Basu, Phys. Lett. A 397, 127265 (2001).

2. B. Coppi and B. Basu (under revision for Physics of Plasmas, 2024).