Plasma Instability During ITBs Formation with Pellet Injection in Tokamak

Abstract

JET H-mode plasma discharge 53212 simulation during the pellet fueling operation in the presence of an internal transport barrier is carried out using the 1.5D BALDUR integrated predictive modelling code. The plasma instability during ITB formation with pellet injection in a tokamak is investigated. These simulations use a neoclassical transport model and an anomalous transport model (either multimode or mixed Bohm/gyro-Bohm core transport model). The boundary condition is described at the top of the pedestal, which is calculated theoretically based on a combination of magnetic and flow shear stabilization pedestal width scaling and an infinite-n ballooning pressure gradient model. The toroidal flow calculation is based on the neoclassical viscosity toroidal velocity model. It was found that the shallower pellet does not destroy the ITB, which locating mainly between r/a = 0.8 and 0.9. Moreover, in the plasma center region (0.4<r/a<0.6) the effective electron thermal diffusivities do not change during the ablation time. However, the effective electron thermal diffusivities decrease after pellet ablation, which means a shallower pellet can improve the internal transport barrier.