Effect of electrode biasing on radial particle and energy fluxes in the edge and SOL regions

Electrode biasing (EB) can modify the plasma turbulence in the edge and SOL regions in a tokamak. This can influence a number of transport processes such as particle and heat exhausts, material recycling etc., that can impact the particle and energy confinement time as well as the heat load on the limiter/divertor plates. We report on numerical simulation studies done in the presence of positive as well as negative EB in the edge region . The simulation results show a reduction of the radial particle and energy fluxes at all the radial positions. The positive biasing increases the fluctuation level of the density and electron temperature but the particle and energy fluxes decrease. We have estimated the fluctuation levels as a function of electric field shear in the presence of positive and negative biasing. We have also investigated the SOL layer thickness as a function of the biasing voltages and calculated the maximum particle and energy densities on the limiter/divertor plates. Such data have been further used to estimate the particle and energy loads (in the parallel direction) on the material plates in the SOL as a function of the radial electric field shear. As these fluxes depend on the blob fraction , therefore, this fraction has been calculated as a function of the radial electric shear obtained from these EB simulations. The fluxes behave nonlinearly with shear. The numerical data have been used to estimate the poloidal wave vector (k_y) spectra and it is found that EB shifts the turbulence towards lower k_y modes. These results have been correlated with the blob fraction as a function of EB and radial electric field shear.