Relaxation to universal non-Maxwellian equilibria in a collisionless plasma

Journal article

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.

Authors: Ewart, RJ; Nastac, ML; Bilbao, PJ; Silva, T; Silva, LO

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: National Academy of Sciences
• Journal: Proceedings of the National Academy of Sciences
• Volume: 122
• Issue: 17
• Article number: e2417813122
• Place of publication: United States
• Publication date: 2025-04-22
• Acceptance date: 2025-03-07
• DOI: 10.1073/pnas.2417813122
• EISSN: 1091-6490
• ISSN: 0027-8424
• Pmid: 40261929
• Language: English
• Keywords: plasma; statistical mechanics; power-law distribution