Transonic plasma flow instabilities in tokamak scrape-off layers: a cause of anomalous diffusion?

The plasma scrape-off layer in a tokamak limiter-controlled discharge involves sonic ion flow down a long narrow flux tube. Small perturbations to such flows can cause large fluctuations which can in turn induce local charge separation, i.e. double sheaths, and further strong fluctuations. It is suggested that these various fluctuations may contribute to the anomalous transport generally observed in scrape-off plasmas. Recent Langmuir probe measurements of fluctuations in the DITE tokamak are consistent with this conjecture.