chapter  7
32 Pages

Binary Collisions

ByRichard D. Hazeltine, François L. Waelbroeck

Turbulent fluctuations, arising from plasma instabilities, are often more important; if the turbulence is sufficiently fine-scaled to conserve local energy and momentum, its statistical effects could be incorporated into a turbulent collision operator. The dominant Coulomb-collisional process is binary, as in a neutral gas, despite the long range of the Coulomb interaction. Strong turbulence theory includes collisional effects in the calculation of fluctuations. The corresponding experimental observation is the formation of extended high-energy tails in all but the most collisional distribution functions. Charge exchange, like unlike-species Coulomb collisions, represents a coupling process—in this case between ions and a neutral species. Charge exchange has the properties one expects of a reasonable binary collision operator: it is bilinear, conservative, has appropriate symmetries and causes entropy to increase. The Brownian response to a random sequence of impulses appears in the kinetic equation as velocity-space diffusion, a key part of the collision operator.