Final Defense

Jingfei Ma, UT-Austin

"The macro- and micro-instabilities in the pedestal region of the Tokamak"

9:00am, RLM 14.318

Abstract: The pedestal region has been considered crucial for the plasma confinement, for it connects the core region where the reaction occurs and the scrape-off layer (SOL) where rich physics such as the heat and particle exhaust, plasma-wall interaction and impurity transport exists. In the High-performance (H-mode) discharge scenarios, the edge transport is suppressed by the shear flow and the pressure profile becomes very steep just inside the separatrix and the ‘pedestal’ is formed. Due to the steep pressure gradient and the edge current, many types of instabilities have been observed in the experiments. Understanding the nature of these instabilities is important for the improvement of the fusion performance, especially for ITER.

Here we report the studies of two major types of instabilities in the pedestal region: (1) the peeling-ballooning modes and the edge-localized modes (ELMs) driven by the pressure gradient and the magnetic curvature; (2) the drift-Alfven modes driven by the electron temperature gradient. The linear characteristics are first analyzed using fluid model and then compared with the simulation results using BOUT++ codes. Moreover, the nonlinear features are also studied numerically and the transport levels for ion and electron are estimated.