Relaxation to universal non-Maxwellian equilibria in a collisionless plasma

• 成果类型: Article
• 署名作者: Ewart, Robert J.; Nastac, Michael L.; Bilbao, Pablo J.; Silva, Thales; Silva, Luis O.; Schekochihin, Alexander A.
• 署名单位: University of Oxford; University of Oxford; University of Oxford; Universidade de Lisboa; University of Oxford
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-10358
• DOI: 10.1073/pnas.2417813122
• 发表日期: 2025-04-22
• 关键词: statistical-mechanics; violent relaxation; acceleration; systems; distributions; turbulence; EVOLUTION; fluid; wave

摘要

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.