Gas puff imaging measurements during resonant magnetic perturbations on the HL-2A tokamak

Abstract

The gas puff imaging diagnostic is used for the investigation of the poloidal flow and turbulent fluctuations at the plasma edge and scrape-off layer (SOL) on the HL-2A tokamak. The impact of resonant magnetic perturbations (RMPs) on the edge poloidal velocity ( ${V_\theta }$ ) are investigated and compared during the operation of a stair-like rising RMP coil current ( ${I_{{\text{RMP}}}}$ ). The application of the RMP is observed to modify the poloidal velocity significantly. When ${I_{{\text{RMP}}}}$ exceeds 4 kA, the turbulence poloidal velocity at the edge changes direction from electron to ion diamagnetic drift. This phenomenon is explained by the electron loss along the perturbed radial magnetic field $({B_r})$ with RMP, with the experimental evidence provided that the edge electric potential increases significantly. A strong impact of the RMP on the properties of plasma density fluctuations in the SOL is also observed. With RMP, both skewness and kurtosis are smaller in the SOL and large-scale turbulence structures (small ${k_r}$ and ${k_\theta }$ ) are suppressed in both edge and SOL. These results can improve our understanding of the interaction between RMP and edge turbulence and in particular, the edge poloidal flow.

Keywords

• RMP
• GPI
• poloidal flow
• large-scale turbulence structures