Scrape‐Off Layer Turbulence Theory

A review is presented of recent developments in the theory of fluctuations in tokamak scrape‐off layers. A brief summary of typical experimental features is presented, followed by derivation of a flute‐mode dispersion relation including conducting‐wall, curvature, axial E × B shear and radial compression drives. Nonlinear results are reviewed, including arguments for and evidence of inverse cascading, penetration of SOL‐generated turbulence into the closed‐flux‐surface edge plasma, and 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 radiative and gas‐target divertors is noted, as is the possibility that SOL turbulence originates in the core plasma. Consequences of SOL turbulence, including broadening of the SOL and dissipating parallel momentum (of potential importance for gas‐target divertors) are outlined, and the possibility of actively exciting turbulence to achieve these objectives is discussed.