Modeling of Drift Displacement of the Pellet Ablated Material for Outboard Side Injection in Large Helical Device

Abstract

The outward drift displacement of the pellet ablated material is studied for low-field side injection in the Large Helical Device (LHD). Stopping of the drift acceleration is shown to be mainly due to the formation of an internal current circuit owing to helical variation of the magnetic field gradient. This process is the most efficient for stopping the cross-field motion of the ablatant in the LHD because, in helical configurations, the parallel scale length of the gradient variation is shorter than in tokamaks. Simulated ablation and deposition profiles are shown to compare well with the H_α emission and post-injection density and temperature profiles.