Investigation of transient transport dynamics induced by compact torus injection in the EAST tokamak

Abstract The rapid increase in plasma core electron temperature triggered by cold plasma injection has long been recognized as compelling evidence of nonlocal transport. This study reports on experiments investigating ‘nonlocal’ thermal transport via compact torus (CT) injection in the plasmas of the EAST tokamak. In low-density plasmas, the core temperature increase following CT injection is accompanied by a drop at the edge. Owing to the CT’s high density, high velocity, and self-organization, rapid penetration into deeper plasma regions was experimentally achieved. In this experiment, the evolution of plasma electron density during CT injection was measured using a high-time-resolution reflectometry for density profile measurement. The evolution of the electron density profile following CT injection is characterized by a rapid increase in core density and subsequent quick flattening of the profile. It has also been found that turbulence plays a crucial role in the mediation of ‘nonlocal’ thermal transport phenomena. The intensity of the quasi-coherent modes (QCMs) in core plasmas, identified by the analysis of Doppler backscattering signals, decreased following CT injection. The simulations based on the trapped gyro-Landau fluid transport model demonstrate that the QCM might be associated with the trapped electron mode (TEM). The observed increase in plasma core temperature after CT injection may be attributed to the stabilization of TEM due to reduction in the core electron density gradient. The simulation results agree well with the experimentally measured core temperature increase after CT injection.