Geon Soo Yoon

The tearing mode (TM) plasma instability was observed in low confinement (L-mode) plasmas when non-axisymmetric magnetic perturbation (MP) was applied using external coils during 2011 campaign of KSTAR. Based on the collected information of the magnetic island location in a plasma, a discharge was designed for suppression of a (2,1) TM mode by adjusting electron cyclotron (EC) launcher angles to the estimated island position. Here, the (m,n) notation describes the poloidal mode number and the to

A design of a modular antenna/detector array for the electron cyclotron emission (ECE) imaging system at the Korea Superconducting Tokamak Advanced Research (KSTAR) is proposed. The modular antenna/detector array is based on a unit antenna/detector module, which consists of an elliptical mini-lens, a dual-dipole antenna, an antenna balun, a low-noise amplifier, and a metal frame. The proposed modular antenna/detector array resolves the problem in the conventional antenna/detector array where one

We studied the effect of finite amplitude, which was ignored in Landau's linearized theory and also studied a transition criterion between linear and nonlinear Landau damping. To adjust the finite amplitude of wave and the initial trapped electron flux J(xT0), we used particle-in-cell simulation that can uniquely modulate these parameters. We predicted on the finite amplitude of wave potential and kinetic energies; these matched the simulation exactly. Oscillation and damping rates in L

The interpretation of electron cyclotron emission (ECE) signal from the optically marginal region of magnetized plasma is presented. The density and the temperature fluctuations associated with the edge localized modes (ELMs) observed in the KSTAR tokamak are estimated by assuming an ELM filamentary structure as a flux tube bulges out like a ballooning mode instability. Synthetic ECE signals from the rotating ELM are calculated based on the measured electron temperature profile and an assumed el

Quasi-coherent mode (QCM) is a widely studied ion-gyroscale micro-instability with characteristics similar to those of trapped electron mode in tokamak plasmas. The effect of the normalized collisionality on the QCM amplitude is quantitatively studied in low-confinement plasmas assisted by electron cyclotron resonant heating in the KSTAR machine using the microwave imaging reflectometer (MIR). To study the evolution of the QCM amplitude by the increased collisionality, coherence lengths are obta