Impact of edge biasing on the cross-field transport and power spectra

Abstract

The impact of positive and negative edge biasing on the interchange plasma turbulence in the edge and scrape-off layer (SOL) regions of a tokamak is assessed by comparing numerical simulation results with and without any biasing. The concomitant modifications in the radial transport and power spectra are also analyzed. It is found that a positive bias shifts the peak of the ky-spectra toward a lower ky value in the edge region, but no such shift takes place in the SOL region. A negative bias produces a negligible shift. The heat and particle fluxes in the edge region are seen to increase with the radial electric field shear in the region where a flow reversal takes place. Elsewhere, the fluxes decrease with an increase in the shear. The heat and particle loads per unit time on the limiter/divertor material plates decrease with the biasing voltages in comparison to those w/o biasing, but the load intensities increase. It is found that the blob fraction decreases with the radial electric field shear, but at lower radial positions around the biasing region, it increases from −16 to +64 V.