Quasineutrality and parallel force balance in kinetic magnetohydrodynamics

Abstract

Kinetic magnetohydrodynamics refers usually to the hybrid fluid and kinetic description of a zero-Larmor-radius collisionless plasma, originally formulated in the classic papers of Kruskal and Oberman (1958) (Kruskal, M. D. and Oberman, C. R. 1958 Phys. Fluids1, 275), Rosenbluth and Rostoker (1959) (Rosenbluth, M. N. and Rostoker, N. 1959 Phys. Fluids2, 23), and Kulsrud (1962) (Kulsrud, R. 1962 Phys. Fluids5, 192). Such a theory is revisited here, as a special limit of the more general description put forward in Ramos (2010, 2011) (Ramos, J. J. 2010 Phys. Plasmas, 17, 082502; Ramos, J. J. 2011 Phys. Plasmas, 18, 102506). The present approach has the advantage of fulfilling the quasineutrality condition and avoiding the redundancy between the fluid and kinetic parallel force balance conditions with a built-in, rigorous account of the parallel electric field, thus affording a clear-cut handling of these issues. At zero-frequency marginal stability, the Rosenbluth–Rostoker fluid closures for the parallel and perpendicular pressures are obtained, in a solution with vanishing parallel electric field and non-zero parallel fluid displacement that satisfies exactly the desired quasineutrality and parallel force balance.