Numerical study on neoclassical tearing mode stabilization via minimum growth rate seeking method

학위논문 (석사)-- 서울대학교 대학원 : 에너지시스템공학부, 2014. 2. 나용수.Neoclassical tearing mode (NTM) is one of critical instabilities which need to be stabilized to achieve high fusion performance. It degrades plasma confinement and sometimes can cause plasma disruptions. Injecting a localized electron cyclotron current drive (ECCD) has been proven experimentally as an effective method to stabilize NTM by replacing the missing bootstrap current in the island. As the efficiency of this method strongly depends on the alignment between the island and the beam deposition, real-time feedback control is essential to achieve robust suppression of NTM. In this thesis, a concept of minimum growth rate seeking control is proposed and the feedback control of the growth rate of the magnetic island is shown to be faster and more efficient than that of the island width. As the minimum growth rate seeking method is a non-model-based control method, it has advantages of no requirement of precise real-time equilibrium reconstruction and EC ray-tracing calculation or NTM plasma system identification. An integrated numerical model is setup for time-dependent simulations of NTM evolution where plasma equilibrium, transport, and heating and CD by EC are coupled with the solver of simplified Rutherford equation in a self-consistent way. It is applied to KSTAR plasmas for reproducing the evolution of the island width in a NTM stabilization experiment. To evaluate the performance of the growth rate control concept, predictive feedback control simulations are performed based on two types of minimum seeking controller in KSTARfinite difference method (FDM) and sinusoidal perturbation. Realistic control input and output parameters are used as the format of measured island growth rates from diagnostics and the poloidal launcher angle, respectively. The results are compared with the minimum island width seeking method. It is revealed that the proposed control concept is less limited in minimum seeking and more robust in reducing misalignment in shorter time scales.Abstract i Contents iii List of Tables iii List of Figures iii Chapter 1 Introduction 1 1.1 Neoclassical tearing mode (NTM) 1 1.2 Stabilization of NTM 2 1.3 Motivations 5 1.4 Objectives and scope of this work 8 Chapter 2 Background of NTM stabilization via minimum seeking method 10 2.1 Principle of minimum seeking method 10 2.2 NTM stabilization via minimum seeking method 14 Chapter 3 Integrated modeling of NTM evolution 17 3.1 Integrated numerical system for NTM simulations 17 3.2 NTM stabilization experiment in KSTAR 21 3.3 Validation of the integrated numerical system with experiment 25 Chapter 4 NTM stabilization simulation via minimum growth rate seeking method 28 4.1 NTM stabilization simulation using minimum growth rate seeking control 28 4.1.1 Minimum growth rate seeking controller 28 4.1.2 Control simulation method 31 4.1.3 Results of NTM stabilization simulation using minimum growth rate seeking control 33 4.2 Comparison with minimum width seeking control 36 4.2.1 Results of FDM based minimum seeking controller 37 4.2.2 Results of sinusoidal perturbation based minimum seeking controller 41 Chapter 5 Conclusion 46 Bibliography 49 국문초록 52Maste

Effects of glucose on hypoxia-induced cardiac cell death

학위논문(박사)--서울대학교 대학원 :약학과 위생화학전공,2004.Docto