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Title: High-beta steady-state research with integrated modeling in the JT-60 Upgrade

Abstract

Improvement of high-beta performance and its long sustainment was obtained with ferritic steel tiles in the JT-60 Upgrade (JT-60U) [T. Fujita et al., Phys. Plasmas 50, 104 (2005)], which were installed inside the vacuum vessel to reduce fast ion loss by decreasing the toroidal field ripple. When a separation between the plasma surface and the wall was small, high-beta plasmas reached the ideal wall stability limit, i.e., the ideal magnetohydrodynamics stability limit with the wall stabilization. A small rotation velocity of 0.3% of the Alfven velocity was found to be effective for suppressing the resistive wall mode. Sustainment of the high normalized beta value of {beta}{sub N}=2.3 has been extended to 28.6 s ({approx}15 times the current diffusion time) by improvement of the confinement and increase in the net heating power. Based on the research in JT-60U experiments and first-principle simulations, integrated models of core, edge-pedestal, and scrape-off-layer (SOL) divertors were developed, and they clarified complex features of reactor-relevant plasmas. The integrated core plasma model indicated that the small amount of electron cyclotron (EC) current density of about half the bootstrap current density could effectively stabilize the neoclassical tearing mode by the localized EC current accurately aligned to the magneticmore » island center. The integrated edge-pedestal model clarified that the collisionality dependence of energy loss due to the edge-localized mode was caused by the change in the width of the unstable mode and the SOL transport. The integrated SOL-divertor model clarified the effect of the exhaust slot on the pumping efficiency and the cause of enhanced radiation near the X-point multifaceted asymmetric radiation from edge. Success in these consistent analyses using the integrated code indicates that it is an effective means to investigate complex plasmas and to control the integrated performance.« less

Authors:
 [1]
+ Show Author Affiliations
  1. Fusion Research and Development Directorate, Japan Atomic Energy Agency, Naka, Ibaraki 311-0193 (Japan)
Publication Date:
OSTI Identifier:
20975052
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 5; Other Information: DOI: 10.1063/1.2718518; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BOOTSTRAP CURRENT; CYCLOTRONS; EDGE LOCALIZED MODES; ELECTRONS; ENERGY LOSSES; FERRITIC STEELS; HIGH-BETA PLASMA; JT-60 TOKAMAK; JT-60U TOKAMAK; MAGNETOHYDRODYNAMICS; NEOCLASSICAL TRANSPORT THEORY; PLASMA SCRAPE-OFF LAYER; SIMULATION; TEARING INSTABILITY; WALLS

Citation Formats

Ozeki, T. High-beta steady-state research with integrated modeling in the JT-60 Upgrade. United States: N. p., 2007. Web. doi:10.1063/1.2718518.
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Ozeki, T. High-beta steady-state research with integrated modeling in the JT-60 Upgrade. United States. doi:10.1063/1.2718518.
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Ozeki, T. Tue . "High-beta steady-state research with integrated modeling in the JT-60 Upgrade". United States. doi:10.1063/1.2718518.
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@article{osti_20975052,
title = {High-beta steady-state research with integrated modeling in the JT-60 Upgrade},
author = {Ozeki, T.},
abstractNote = {Improvement of high-beta performance and its long sustainment was obtained with ferritic steel tiles in the JT-60 Upgrade (JT-60U) [T. Fujita et al., Phys. Plasmas 50, 104 (2005)], which were installed inside the vacuum vessel to reduce fast ion loss by decreasing the toroidal field ripple. When a separation between the plasma surface and the wall was small, high-beta plasmas reached the ideal wall stability limit, i.e., the ideal magnetohydrodynamics stability limit with the wall stabilization. A small rotation velocity of 0.3% of the Alfven velocity was found to be effective for suppressing the resistive wall mode. Sustainment of the high normalized beta value of {beta}{sub N}=2.3 has been extended to 28.6 s ({approx}15 times the current diffusion time) by improvement of the confinement and increase in the net heating power. Based on the research in JT-60U experiments and first-principle simulations, integrated models of core, edge-pedestal, and scrape-off-layer (SOL) divertors were developed, and they clarified complex features of reactor-relevant plasmas. The integrated core plasma model indicated that the small amount of electron cyclotron (EC) current density of about half the bootstrap current density could effectively stabilize the neoclassical tearing mode by the localized EC current accurately aligned to the magnetic island center. The integrated edge-pedestal model clarified that the collisionality dependence of energy loss due to the edge-localized mode was caused by the change in the width of the unstable mode and the SOL transport. The integrated SOL-divertor model clarified the effect of the exhaust slot on the pumping efficiency and the cause of enhanced radiation near the X-point multifaceted asymmetric radiation from edge. Success in these consistent analyses using the integrated code indicates that it is an effective means to investigate complex plasmas and to control the integrated performance.},
doi = {10.1063/1.2718518},
journal = {Physics of Plasmas},
number = 5,
volume = 14,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
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Journal Article:
DOI:  10.1063/1.2718518
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  • - Physics of Plasmas
    Researches on advanced tokamak (AT) have progressed with integrated modeling in JT-60 Upgrade [N. Oyama et al., Nucl. Fusion 49, 104007 (2009)]. Based on JT-60U experimental analyses and first principle simulations, new models were developed and integrated into core, rotation, edge/pedestal, and scrape-off-layer (SOL)/divertor codes. The integrated models clarified complex and autonomous features in AT. An integrated core model was implemented to take account of an anomalous radial transport of alpha particles caused by Alfven eigenmodes. It showed the reduction in the fusion gain by the anomalous radial transport and further escape of alpha particles. Integrated rotation model showed mechanismsmore » of rotation driven by the magnetic-field-ripple loss of fast ions and the charge separation due to fast-ion drift. An inward pinch model of high-Z impurity due to the atomic process was developed and indicated that the pinch velocity increases with the toroidal rotation. Integrated edge/pedestal model clarified causes of collisionality dependence of energy loss due to the edge localized mode and the enhancement of energy loss by steepening a core pressure gradient just inside the pedestal top. An ideal magnetohydrodynamics stability code was developed to take account of toroidal rotation and clarified a destabilizing effect of rotation on the pedestal. Integrated SOL/divertor model clarified a mechanism of X-point multifaceted asymmetric radiation from edge. A model of the SOL flow driven by core particle orbits which partially enter the SOL was developed by introducing the ion-orbit-induced flow to fluid equations.« less

  • - Physics of Plasmas
    Recent results from steady-state sustainment of high-{beta} plasma experiments in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) tokamak [A. Kitsunezaki et al., Fusion Sci. Technol. 42, 179 (2002)] are described. Extension of discharge duration to 65 s (formerly 15 s) has enabled physics research with long time scale. In long-duration high-{beta} research, the normalized beta {beta}{sub N}=2.5, which is comparable to that in the steady-state operation in International Thermonuclear Experimental Reactor (ITER) [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], has been sustained for about 15 s with confinement enhancement factor H{submore » 89PL} above 2, where the duration is about 80 times energy confinement time and {approx}10 times current diffusion time ({tau}{sub R}). In the scenario aiming at longer duration with {beta}{sub N}{approx}1.9, which is comparable to that in the ITER standard operation scenario, duration has been extended to 24 s ({approx}15{tau}{sub R}). Also, from the viewpoint of collisionality and Larmor radius of the plasmas, these results are obtained in the ITER-relevant regime with a few times larger than the ITER values. No serious effect of current diffusion on instabilities is observed in the region of {beta}{sub N} < or approx. 2.5, and in fact neoclassical tearing modes (NTMs), which limit the achievable {beta} in the stationary high-{beta}{sub p} H-mode discharges, are suppressed throughout the discharge. In high-{beta} research with the duration of several times {tau}{sub R}, a high-{beta} plasma with {beta}{sub N}{approx}2.9-3 has been sustained for 5-6 s with two scenarios for NTM suppression: (a) NTM avoidance by modification of pressure and current profiles, and (b) NTM stabilization with electron cyclotron current drive (ECCD)/electron cyclotron heating (ECH). NTM stabilization with the second harmonic X-mode ECCD/ECH has been performed, and it is found that EC current density comparable to bootstrap current density at the mode location is required for complete stabilization. Structure of a magnetic island associated with an m/n=3/2 NTM has been measured in detail (m and n are poloidal and toroidal mode numbers, respectively). By applying newly developed analysis method using motional Stark effect (MSE) diagnostic, where change in current density is directly evaluated from change in MSE pitch angle without equilibrium reconstruction, localized decrease/increase in current density at the mode rational surface is observed for NTM growth/suppression. In addition, it is found that characteristic structure of electron temperature perturbation profile is deformed during NTM stabilization. Hypothesis that temperature increase inside the magnetic island well explains the experimental observations. It is also found that the characteristic structure is not formed for the case of ECCD/ECH before the mode, while the structure is seen for the case with ECCD/ECH just after the mode onset, suggesting the stronger stabilization effect of the early EC wave injection.« less

  • ; - Physics of Plasmas
    High {ital I}{sub {ital P}} hot ion high confinement (H) mode at {ital I}{sub {ital P}} up to 4.5 MA has been exploited. Sawtooth stabilization by ion cyclotron range of frequencies (ICRF) heating is effective to improve performance in this regime. The performance is limited by the onset of giant edge localized modes (ELMs). It was found that the edge pressure gradient at the onset of ELMs can be increased with increasing triangularity {delta} up to 0.4 at {ital I}{sub {ital P}}{lt}1.2 MA. The normalized beta ({beta}{sub {ital N}}) value at the ELM onset also increases from {approximately}1 to {approximately}2.8more » when {delta} is increased from {approximately}0.1 to {approximately}0.33, respectively. In the reversed-shear operation, an internal transport barrier (ITB) appears, not only for the ions but also for the electrons. The improved confinement region is quite large (within {ital r}/{ital a}{approximately}0.65). The highest confinement enhancement factor (H factor) and {beta}{sub {ital N}} achieved so far are, respectively, 2.6 and 2.4 for reversed-shear plasmas. A scaling law of the H-mode threshold power, which is consistent with the International Thermonuclear Experimental Reactor (ITER) [Y. Shimomura, Phys. Plasmas {bold 1}, 1612 (1994)] scaling, is derived. The power threshold for ITB formation in the high {beta}{sub {ital p}} mode depends on the electron density, but not on the toroidal field. It is validated that the control of the toroidal rotation is effective to control toroidicity-induced Alfv{acute e}n eigenmodes (TAE modes). {copyright} {ital 1996 American Institute of Physics.}« less

  • ; - Physics of Plasmas
    This paper describes the latest achievements of the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) [H. Kimura and the JT-60 Team, Phys. Plasmas {bold 3}, 1943 (1996)] for the establishment of the physics and technology basis for steady-state, fully noninductive current-drive plasmas with high fusion performance. Recent results are highlighted by (1) high performance reversed-magnetic-shear discharges [an idealized equivalent Q{sub DT} of 1.05, a confinement-enhancement factor (H factor) of 3.23, and a normalized beta value ({beta}{sub N}) of 1.88 at I{sub p}=2.8MA/P{sub abs}=17MW]; the first observation of thermal transport barriers both for electrons and ions, (2) the first injectionmore » of negative-ion-based neutral deuterium beams in the world for studies of current drive, heating, and high-energy particle behavior (achieved so far: 2.5 MW/400 keV, design values: 10 MW/500 keV); high neutralization efficiency of 60{percent} at 370 keV; high current drive efficiency of {eta}{sub CD}=8{times}10{sup 18}m{sup {minus}2}A/W, (3) improved giant edge-localized-mode (ELM) limit and normalized beta limit by high triangularity ({delta}) shaping; the quasi-steady-state ELMy plasmas with integrated high performance were sustained for 8 times the energy confinement time ({delta}=0.35, H=2.5, {beta}{sub N}=2.5 at I{sub p}=1.5MA and B{sub t}=3.6T), and (4) enhanced divertor radiation and detached divertor in reversed-shear discharges with neon puffing, while the internal transport barrier was sustained. {copyright} {ital 1997 American Institute of Physics.}« less

  • - Physics of Plasmas
    The duration of advanced tokamak plasma operation in JT-60 Upgrade (JT-60U) [A. Kitsunezaki et al., Fusion Sci. Technol. 42, 179 (2002)] has been extended on long time scales exceeding the current diffusion time ({tau}{sub R}) and close to the wall saturation time. A very high bootstrap current fraction (f{sub BS}) of 75% was maintained for 7.4 s (2.7{tau}{sub R}), while a normalized beta of 2.5 was maintained for 15.5 s ({approx}9.5{tau}{sub R}). The current profile reaches stationary conditions in {approx}{tau}{sub R} for the small f{sub BS} regime, while a longer time is required for the large f{sub BS} regime. Amore » plasma with a weak shear q profile, similar to requirements for the ITER steady-state operational scenario, was successfully maintained. The particle inventory in the wall was observed to saturate in repeated long-pulse ({approx}30 s) H-mode discharges with edge localized modes. The analysis of neutral particles in the scrape-of-layer plasma indicates different time scales are involved for the wall saturation. Ferritic steel tiles have been installed in the vacuum vessel to reduce the toroidal field ripple towards extending the advanced tokamak regime further in the coming operational campaign.« less