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arXiv · 2409.01742

Relaxation to universal non-Maxwellian equilibria in a collisionless plasma

Robert J. Ewart·Michael L. Nastac·Pablo J. Bilbao·Thales Silva·Luís O. Silva·Alexander A. Schekochihin
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Abstract

Generic equilibria are derived for turbulent relaxing plasmas via an entropy-maximization procedure that accounts for the short-time conservation of certain collisionless invariants. The conservation of these collisionless invariants endows the system with a partial `memory' of its prior conditions, but is imperfect on long time scales due to the development of a turbulent cascade to small scales, which breaks the precise conservation of phase volume, making this memory imprecise. The equilibria are still determined by the short-time collisionless invariants, but the invariants themselves are driven to a universal form by the nature of the turbulence. This is numerically confirmed for the case of beam instabilities in one-dimensional electrostatic plasmas, where sufficiently strong turbulence appears to cause the distribution function of particle energies to develop a universal power-law tail, with exponent -2.

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Robert J. Ewart, Michael L. Nastac, Pablo J. Bilbao, Thales Silva, Luís O. Silva, Alexander A. Schekochihin. 2024-09-03. Relaxation to universal non-Maxwellian equilibria in a collisionless plasma. https://arxiv.org/abs/2409.01742

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