Advances in physics of the magneto-hydro-dynamic and turbulence-based instabilities in toroidal plasmas via 2-D/3-D visualization

A robust theoretical framework for describing the explosive growth of the magneto-hydro-dynamic (MHD) and turbulence-based instabilities in toroidal plasmas can only be achieved through a conclusive validation of the physics model with undisputable experimental information. Recently new techniques for high precision measurements of their 2-D/3-D structures such as the electron cyclotron emission imaging (ECEi) and microwave imaging reflectometry (MIR) systems, have been deployed to explore new and detailed physics information of these instabilities in a number of toroidal devices including KSTAR. For sawtooth instability, validation of q 0 > 1.0 after the crash supports the “full reconnection model” where an axisymmetric 1/1 kink mode is assumed with a slow crash time. But the majority of crash events are characterized fast time scale with a highly non-axisymmetric 1/1 kink mode during the crash phase and only non-axisymmetry part is supported by the ballooning mode model. Precision 2-D measurements have significantly increased the accuracy and confidence in determining the stability parameters of the 2/1 tearing mode, and turbulence dynamics in the presence of the 2/1 tearing mode is explored together with the relevant theoretical modeling. Edge Localized Modes (ELM) have been validated with linear and non-linear theoretical models to reveal exciting new dynamics such as the in–out asymmetry, time evolution from growth to burst, etc. The role of turbulence induced by the resonant magnetic perturbation (RMP) in control of the ELM-crash has also been investigated. These study results may guide us to identifying the key nonlinear physics critical for advancing the theoretical modeling required to control harmful MHD and micro-turbulence instabilities.