Stochastization and pump-out in edge plasma caused by edge localized modes

Abstract

Mechanisms of current generation in edge localized mode (ELM) filaments are discussed. It is shown that dipole type currents should flow in the filaments and that these currents are short-circuited through the ambient plasma of the scrape-off layer. The steady-state monopole currents in the filaments cannot be closed through the ambient plasma and oscillatory currents with Alfven frequency should emerge instead. The dipole type currents in the filaments are sufficient to produce magnetic field perturbations which create a stochastic layer inside the edge transport barrier (ETB) region. The dynamic of penetration of the magnetic field perturbations is analyzed and it is shown that the corresponding time is comparable with the life time of the filaments. At the stage when the ETB region is stochastized by the currents of the filaments the radial electric field becomes less negative or even positive inside the ETB and the onset of outward convective flux takes place. It is shown that this outward flux could lead to the significant pump-out effect—the density decrease in the pedestal region.