Analysis of the plasma blob formation/transport and its effects on impurity transport in the scrape-off layer regions

The purpose of this study was to clarify the effects of a plasma blob on the impurity transport in the scrape-off layer (SOL) and divertor region of fusion devices. As a first step, plasma blob formation and transport were simulated by a two-dimensional interchange turbulence model. Its effects on impurity transport were studied by the impurity equations of motion in the trace impurity limit. The results show that a blob is produced by the interchange instability and transported radially towards the wall by the E × B drift due to the polarization electric field by the charge separation between ions and electrons inside the blob due to their magnetic drifts. The polarization electric field also induces the impurity radial E × B drift and the resultant impurity radial transport at least for impurities with a small Larmor radius in comparison with the blob size. These first results provide us with a robust basis for a more systematic study (e.g., dependence of impurity mass and charge state) and for a more quantitative evaluation of the effects of the blob on the impurity transport in the SOL and divertor region.