Electromagnetic properties of hot collisionless plasma in magnetic reconnection regions

Abstract

Investigation of magnetic reconnection processes in a hot collisionless space plasma requires development of new methods for a self-consistent description of plasma dynamics in the region of an X-type magnetic field B(r),where kinetic effects of resonant and nonresonant interaction of particles and fields are important and the conventional MHD description is inadequate. Inside the reconnection regions, there is a very strong electric field E(r),which accelerates particles and produces a plasma flow with a self-consistent plasma sheet, which is known as Sweet-Parker flow. The fine structure of fields, currents, and flows in such a hot collisionless plasma remains unclear and needs special examination. In the analytical investigation, we confine ourselves to the internal part of the reconnection region, where the electric field is much stronger than the magnetic field, ¦E¦≫¦B¦.We observe a regular behavior of particles there and develop a perturbation method for Maxwell's and Vlasov's equations. The electric field is often related to inductive fields, but we focus mainly on time-invariant reconnection processes and consider a stationary electric field imposed externally and defined by external boundary conditions. In a zeroth order approximation, the magnetic field is absent, and the particles are stationary and have equilibrium distribution between acceleration and deceleration in the homogeneous electric field E₀.This field is a free parameter of the problem and produces a new scale of length τ _Eα =1/(-ik) _Eα where k _Eα =iq _α E ₀/T _α, and a scale of frequency ω _Eα =-ik _Eα v _α for reconnection scaling. The linear response of the particles under fields E ₁ (r) and B ₁ (r) and the distributions of flow velocity u ₁ (r),charge ρ₁(r),and current j ₁ (r) are found by integrating along the particle trajectory in the homogeneous electric field. The external electric field E ₀ redefines the linear electromagnetic properties of the plasma and connects, in particular, the electrostatic and electromagnetic modes via drift terms. As a result, we obtain a system of linear integral equations with external sources for a self-consistent description of the plasma behavior in regions with a strong accelerating magnetic field. We explore these regions in a small-scale field limit (kτ _Eα ≫1),using a local approximation.