Effect of dynamical friction on interchange motion of plasma filaments

Theory and numerical simulations are presented for interchange motion of plasma filaments in the presence of dynamical friction and allowing large relative filament amplitudes. When friction is negligible, the filament velocity is proportional to the square root of gravity and its cross-field size. For strong friction, the filament velocity is independent of the cross-field size, proportional to gravity, and inversely proportional to the friction coefficient. In this frictional regime, the filament moves a large distance with nearly constant velocity and shape. The transition between these velocity scaling regimes and the amplitude dependence are revealed. The results presented here complement previous theories for irregularities in the equatorial ionosphere and are in excellent agreement with recent experiments on simply magnetized toroidal plasmas. The relevance to blob-like structures in the scrape-off layer of magnetically confined plasmas is also discussed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704793]