Nonquasineutral current equilibria as elementary structures of plasma dynamics
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- Gordeev, A.V. Plasma Phys. Rep. (2010) 36: 30. doi:10.1134/S1063780X10010034
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A study is made of the fundamental features of current filaments with a nonzero electron vorticity Ωe ≡ B − (c/e) ▿ × pee ≠ 0 and the corresponding Lagrangian invariant Ie. Such current structures can exist on spatial scales of up to ωpi−1. It is shown that the dissipative stage of the plasma evolution and the violation of Thomson’s theorem on vorticity conservation in an electron fluid are of fundamental importance for the onset of electron current structures. A key role of the screening of electric and magnetic fields at distances on the order of the magnetic Debye radius rB = B/(4πene)—the main property of such current structures in a Hall medium with σB/(enec) ≫ 1—is stressed. Since the minimum size of a vortex structure is the London length c/ωpe, the structures under consideration correspond to the condition rB > c/ωpe or B2 > 4πnemec2, which leads to strong charge separation in the filament and relativistic electron drift. It is demonstrated that the specific energy content in current structures is high at a filament current of 10–15 kA: from 100 J/cm3 at a plasma density of 1014 cm−3 (the parameters of a lightning leader) to 107J/cm3 for a fully ionized atmospheric-pressure air. Estimates are presented showing that the Earth’s ionosphere, circumsolar space, and interstellar space are all Hall media in which current vortex structures can occur. A localized cylindrical equilibrium with a magnetic field reversal is constructed—an equilibrium that correlates with the magnetic structures observed in intergalactic space. It is shown that a magnetized plasma can be studied by using evolutionary equations for the electron and ion Lagrangian invariants Ie and Ii. An investigation is carried out of the evolution of a current-carrying plasma in a cylinder with a strong external magnetic field and with a longitudinal electron current turned on in the initial stage—an object that can serve as the simplest electrodynamic model of a tokamak. In this case, it is assumed that the plasma conductivity is low in the initial stage and then increases substantially with time. Based on the conservation of the integral momentum of the charged particles and electromagnetic field in a plasma cylinder within a perfectly conducting wall impenetrable by particles, arguments are presented in support of the generation of a radial electric field in a plasma cylinder and the production of drift ion fluxes along the cylinder axis. A hypothesis is proposed that the ionized intergalactic gas expands under the action of electromagnetic forces.