M.J. Choi

Two-dimensional imaging of edge-localized modes in KSTAR plasmas unperturbed and perturbed by n=1 external magnetic fields

The temporal evolution of edge-localized modes (ELMs) has been studied using a 2-D electron cyclotron emission imaging system in the KSTAR tokamak. The ELMs are observed to evolve in three distinctive stages: the initial linear growth of multiple filamentary structures having a net poloidal rotation, the interim state of regularly spaced saturated filaments, and the final crash through a short transient phase characterized by abrupt changes in the relative amplitudes and distance among filaments. The crash phase, typically consisted of multiple bursts of a single filament, involves a complex dynamics, poloidal elongation of the bursting filament, development of a fingerlike bulge, and fast localized burst through the finger. Substantial alterations of the ELM dynamics, such as mode number, poloidal rotation, and crash time scale, have been observed under external magnetic perturbations with the toroidal mode number n = 1.

Comparison of measured 2D ELMs with synthetic images from BOUT++ simulation in KSTAR

A detailed study of edge-localized mode (ELM) dynamics in the KSTAR tokamak is performed using a two-dimensional (2D) electron cyclotron emission imaging (ECEI) diagnostic system. Highly coherent mode structures rotating in the poloidal view plane are routinely observed in the inter-ELM pedestal region where the optical thickness for ECE rapidly changes and the interpretation of emission intensity is complicated. To have confidence on the measurements, the observed images are compared with synthetic images of the ELM structure deduced from three-field BOUT++ simulations. The synthetic process considers instrumental effects of the ECEI diagnostic, intrinsic broadening of the ECE and background noise. The synthetic 2D images highly resemble the observed structure, providing confidence that the ELM dynamics can be visualized by ECEI.

Multiscale interaction between a large scale magnetic island and small scale turbulence

Multiscale interaction between the magnetic island and turbulence has been demonstrated through simultaneous two-dimensional measurements of turbulence and temperature and flow profiles. The magnetic island and turbulence mutually interact via the coupling between the electron temperature (

E × B flow velocity deduced from the poloidal motion of fluctuation patterns in neutral beam injected L-mode plasmas on KSTAR

T_e

2D/3D electron temperature fluctuations near explosive MHD instabilities accompanied by minor and major disruptions

) gradient, the

Distinct stages of radio frequency emission at the onset of pedestal collapse in KSTAR H-mode plasmas

T_e

Investigation of instabilities and rotation alteration in high beta KSTAR plasmas

turbulence, and the poloidal flow. The

Appearance and Dynamics of Helical Flux Tubes under Electron Cyclotron Resonance Heating in the Core of KSTAR Plasmas

T_e

Improved accuracy in the estimation of the tearing mode stability parameters (Δ′ and wc) using 2D ECEI data in KSTAR

gradient altered by the magnetic island is peaked outside and flattened inside the island. The

Nonlinear Interaction of Edge-Localized Modes and Turbulent Eddies in Toroidal Plasma under n=1 Magnetic Perturbation.

T_e