Pattern formation in Vlasov-Poisson plasmas beyond Landau caused by the continuous spectra of electron and ion hole equilibria

TL;DR

This paper reviews an advanced nonlinear wave theory for Vlasov-Poisson plasmas, emphasizing the importance of continuous spectra and trapped particle effects in pattern formation beyond traditional Landau theory.

Contribution

It introduces a nonlinear framework that accounts for continuous spectra and trapped particles, correcting limitations of linear Landau theory and expanding understanding of plasma pattern formation.

Findings

Linear stability analysis shows unconditional marginal stability independent of electron-ion drift.

Negative energy holes act as attractors, fueling turbulence.

Nonlinear wave models are essential for understanding collisionless plasma patterns.

Abstract

This review presents an upgraded wave theory adapted to the high fluctuation level of driven realistic i.e. non-idealized plasmas. Above all, this means giving up the well-known concept of a linear wave theory in favor of a thoroughly nonlinear theory. Based on the author's early publication (H. Schamel, Plasma Phys. 14 (1972) 905) and supported by recent Vlasov-Poisson simulations of realistic noisy plasmas, an extended framework is presented which not only covers the essential features of coherent hole structures, but which also enables to make the necessary corrections to the current wave theory. These corrections are long overdue and can be briefly summarized under the heading: loss of linear Vlasov dynamics when adequately addressing equilibrium states (i.e. failure of linear Landau theory and of continuous van Kampen spectra, respectively). A linear stability analysis for single harmonic waves that successfully incorporates trapped particle effects (in contrast to previous analyses) shows an unconditional marginal stability independent of the drift between electrons and ions, which irrevocably contradicts Landau's theory. Moreover, holes of negative energy are of particular interest because they act as attractors in the dynamical system. They are the source for the release of further modes and thus increase the level of intermittent turbulence. In summary, pattern formation in collisionless plasmas is inherently nonlinear and kinetic. However, to have a satisfactory, if not yet complete, understanding of its processes a twofold paradigm shift is imperative: one from the conventional linear, discrete wave models to the nonlinear wave models dealing with continuous spectra due to trapping and a second from the BGK to the present method for the correct handling of equilibria.