A theoretical study is made of the effect of edge biasing on the dynamics of the interchange turbulence in the edge and scrape-off layer (SOL) regions. A linear analysis of a set of model fluid equations shows that biasing stabilizes the small ky modes. The model equations are next solved numerically, using the BOUT++ framework, to explore the nonlinear dynamics in the presence of positive or negative bias and compared to results in the absence of bias. Positive biasing is found to lead to a larger increment in plasma density and temperature as compared to negative biasing. It is further observed that cross-correlation between density and poloidal electric field at different radial positions decreases for positive biasing and in the case of negative biasing it is almost similar to that of no biasing. Plasma density and poloidal electric field fluctuations have been investigated which show that the density fluctuations increase (decrease) for positive (negative) biasing but the radially outward flux for these biasing cases always decreases mainly due to the decrease of cross-correlation between density and poloidal electric field fluctuations.

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.

The effects of nitrogen gas seeding in the edge and scrape-off layer (SOL) regions of a tokamak plasma are studied through 2D fluid simulations using the BOUT++ code. Proper account is taken of the presence of multiple charged states of nitrogen ions due to ionization, recombination, and dissociation processes, and a self-consistent study of the interaction of these ions with the turbulent plasma in the edge and SOL regions is carried out. The self-consistent model includes the effects of polarization drifts of the main plasma and impurity ions for determining the plasma vorticity. Nitrogen seeding is found to modify the turbulence as well as to influence the profiles of the equilibrium plasma density and the electron temperature. The densities of N3+ to N5+ ions are found to be relatively higher than the other charged states. This is understood and further validated by a 0D simulation. The radial profiles of these impurity ions are mapped, and their radiation energy losses are estimated. The radial profile of the radiation losses is maximum near to the edge-to-SOL transition region and becomes broader in the edge region than the SOL region.