Non-thermal particle acceleration and power-law tails via relaxation to universal Lynden-Bell equilibria

Journal article

Collisionless and weakly collisional plasmas often exhibit non-thermal quasi-equilibria. Among these quasi-equilibria, distributions with power-law tails are ubiquitous. It is shown that the statistical-mechanical approach originally suggested by Lynden-Bell (Mon. Not. R. Astron. Soc., vol. 136, 1967, p. 101) can easily recover such power-law tails. Moreover, we show that, despite the apparent diversity of Lynden-Bell equilibria, a generic form of the equilibrium distribution at high energies is a ‘hard’ power-law tail ∝ε−2, where ε is the particle energy. The shape of the ‘core’ of the distribution, located at low energies, retains some dependence on the initial condition but it is the tail (or ‘halo’) that contains most of the energy. Thus, a degree of universality exists in collisionless plasmas.

Authors: Ewart, RJ; Nastac, ML; Schekochihin, AA

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Cambridge University Press
• Journal: Journal of Plasma Physics
• Volume: 89
• Issue: 5
• Article number: 905890516
• Publication date: 2023-10-20
• Acceptance date: 2023-09-04
• DOI: 10.1017/S0022377823000983
• EISSN: 1469-7807
• ISSN: 0022-3778
• Language: English
• Keywords: astrophysical plasmas; plasma nonlinear phenomena; space plasma physics