  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.
