SCRAPE-OFF LAYER TURBULENCE THEORY

A review is presented of recent developments in the theory of fluctuat ions in tokamak scrape-off layers. A brief summary of typical experime ntal features is presented, followed by derivation of a flute-mode dis persion relation including conducting-wall, curvature, axial E x B she ar and radial compression drives. Non-linear results are reviewed, inc luding arguments for and evidence of inverse cascading, penetration of SOL-generated turbulence into the closed-flux-surface edge plasma, an d large-amplitude fluid excursions, comparable to observed SOL widths. Effects of divertor and limiter geometry, including x-point effects, are discussed. The potential importance of atomic physics drives for r adiative and gas-target divertors is noted, as is the possibility that SOL turbulence originates in the core plasma. Consequences of SOL tur bulence, including broadening of the SOL and dissipating parallel mome ntum (of potential importance for gas-target divertors) are outlined, and the possibility of actively exciting turbulence to achieve these o bjectives is discussed.