Nonlinear simulation of edge localized mode with pressure profile modified by pellet injection through extended BOUT++ MHD code

Abstract A BOUT++ three-field MHD model is extended and applied to study the effect of the pedestal pressure profile modified by the pellet injection from the low field side on the nonlinear behaviors of ELM. The linear simulation shows that the growth rates of all n modes can be enhanced regardless of the deposition location and are more affected by the pellet atoms depositing in the middle of the steep pedestal region. From the nonlinear simulation, an ELM triggering threshold for the rate of the modified pressure over the unperturbed one at the most affected position is demonstrated when the pellet deposits its atoms on the pedestal top, which supports the observation in the non-fuel pellet pacing experiments on EAST. In contrast, when the pellet deposits its atoms within the steep pedestal region, the ELM size is increased at low and high rates but decreased in an intermediate range; compared with the deposition mainly on the pedestal top, fewer perturbed atoms introduced to the steep pedestal region could cause a larger ELM size, which can somehow explain the probabilistic behavior of ELM triggering by small pellet injection on EAST.