Thawatchai Onjun

Magnetohydrodynamic-calibrated edge-localized mode model in simulations of International Thermonuclear Experimental Reactor

Self-consistent simulations of the International Thermonuclear Experimental Reactor (ITER) [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)] have been carried out using the JETTO-integrated modeling code in which theory-motivated models are used for the H-mode pedestal and for the stability conditions that lead to the edge-localized mode (ELM) crashes. Transport is described by combining the anomalous mixed Bohm/gyro-Bohm model [M. Erba, A. Cherubini, V. V. Parail, and A. Taroni, Plasma Phys. Controlled Fusion 39, 261 (1997)] with the NCLASS neoclassical transport model [W. A. Houlberg, K. C. Shaing, S. P. Hirshman, and M. C. Zarnstorff, Phys. Plasmas 4, 3231 (1997)] in the core region, while only neoclassical transport is used in the pedestal region. In the simulations, an ELM crash can be triggered either by a pressure-driven ballooning mode or by a current-driven peeling mode, depending on which instability reaches its stability criterion first. The equilibrium ...

Interplay between ballooning and peeling modes in simulations of the time evolution of edge localized modes

The time evolution of edge localized modes (ELMs) in the Joint European Torus tokamak [P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985)] is investigated using the JETTO predictive modeling code [M. Erba et al., Plasma Phys. Controlled Fusion 39, 261 (1997)]. It is found that both pressure-driven ballooning and current-driven peeling modes can play a role in triggering the ELM crashes. In the simulations carried out, each large ELM consists of a sequence of quasicontinuous small ELM crashes. Each sequence of ELM crashes is separated from the next sequence by a relatively longer ELM-free period. The initial crash in each ELM sequence can be triggered either by a pressure-driven ballooning mode or by a current-driven peeling mode, while the subsequent crashes within that sequence are triggered by current-driven peeling modes, which are made more unstable by the reduction in the pressure gradient resulting from the initial crash. The HELENA and MISHKA ideal magnetohydrodynamic stability codes [A. B. Mikhailov...

Effect of isotope mass on simulations of the high-mode pedestal and edge localized modes

Simulations of Joint European Torus (JET) [P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985)] type I high-mode (H-mode) discharges with edge localized modes (ELMs) are used to study the effect of isotope mass on the height of the pedestal and the frequency of ELMs. A dynamic model for the H-mode pedestal and ELM cycles is employed in the JETTO integrated modeling code [M. Erba et al., Plasma Phys. Control. Fusion 39, 261 (1997)]. The stability criteria that are used to trigger ELM crashes in the JETTO simulations are calibrated with the HELENA and MISHKA ideal magnetohydrodynamic (MHD) stability codes [A. B. Mikhailovskii et al., Plasma Phys. Rep. 23, 713 (1997)]. Results obtained using a pedestal model in which the pedestal width increases with isotope mass are compared with those obtained using a fixed, prescribed pedestal width. In JET type I ELMy H-mode discharges, it is found that the height of the pressure pedestal increases and that the frequency of the ELMs decreases as the isotope mass is increase...

STUDY OF L–H TRANSITION AND PEDESTAL WIDTH BASED ON TWO-FIELD BIFURCATION AND FIXED POINT CONCEPTS

The L–H transition in magnetic confinement plasmas is investigated on the basis of concepts of two-field bifurcation and fixed-point stability. A set of heat and particle transport equations with both neoclassical and anomalous effects included is used to study ETB formation and also pedestal width and dynamics. It is found that plasmas can exhibit bifurcation where a sudden jump in the gradients can be achieved at the transition point corresponding to the critical flux. Furthermore, it is found that the transport barrier expands inward, whereby the radial growth of the pedestal initially appears to be superdiffusive but later slows down and stops. In addition, the time of barrier expansion is found to be much longer than the time that plasma takes to evolve from L-mode to H-mode. A sensitivity study is also performed, in which the barrier width is found to be sensitive to various parameters, e.g. heating, transport coefficients and suppression strength.

Determination of the total inductance of TPF-I

Thailand Plasma Focus I (TPF-I) is a dense plasma focus device which was developed as a collaborative project among Thailand Institute of Nuclear Technology, Sirindhorn International Institute of Technology and Thammasat university. It aims to be a radiation source for academic research. This device has a power of 6 kJ. In this work, a Rogowski coils was used for measuring high speed current pulse to capture electric signal during operation TPF-I. By determining period of the discharge, it was found that the total inductance of TPF-I is about 216±12 nH, which is in agreement with Lee model.

The simulation of L-H transition in tokamak plasma using MMM95 transport model

BALDUR integrative predictive modelling code together with a Multimode (MMM95) anomalous transport model is used to simulate the evolution profiles, including plasma current, temperature, density and energy in a tokamak reactor. It is found that a self - transition from low confinement mode (L-mode) to high confinement mode (H-mode) regimes can be achieved once a sufficient auxiliary heating applied to the plasma is reached. The result agrees with experimental observations from various tokamaks. A strong reduction of turbulent transport near the edge of plasma is also observed, which is related to the formation of steep radial electric field near the edge regime. From transport analysis, it appears that the resistive ballooning mode is the dominant term near the plasma edge regime, which is significantly reduced during the transition.

Preliminary numerical study of Thailand Plasma Focus II (TPF-II) design

In this work, we use the Lee model to predict the plasma parameters, such as plasma temperature and pinch duration, in the 3.37 kJ DPF device, called “Thailand Plasma Focus-II (TPF-II).” This numerical result is then used to optimize the electrode parameters for the maximum production rate of 18F. The crossing point of pinch duration and pinch temperature is considered to obtain the appropriate electrode length, anode radius and gas gap between anode and cathode. The gas gap between both electrodes is indicated in ratio between cathode radius and anode radius, c. The results show that the best values of c, anode radius and electrode length are 1.48, 1.2 cm and 26.1 cm, respectively, in which the plasma pinch temperature, peak current and pinch duration of 0.76 keV, 207 kA and 8.725 ns can be obtained.