Theory of Phase Space Density Granulation in Plasma

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Abstract
A novel state of turbulent plasma characterized by small scale phase‐space granulations called “clumps” is proposed. Clumps are produced when regions of different phase space density are mixed by the fluctuating electric field. They move along ballistic orbits and drive the turbulent field in a manner similar to that in which thermal fluctuations are driven by particle discreteness. In the coherent wave limit the clumps become the familiar trapped particle eddies of a Bernstein‐Green‐Kruskal mode. The turbulent state can exist in the absence of linear instability although it is more likely to occur in a linearly unstable plasma. The spectrum contains a ballistic portion as well as resonances at the wave (collective) frequencies. The discreteness of the clumps produces collision‐like process. For example, the average distribution function satisfies a Fokker‐Planck equation instead of a quasilinear diffusion equation.