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Yamaguchi, Taiki; Kawano, Yasunori; Fujieda, Hirobumi; Kurihara, Kenichi; Sugihara, Masayoshi*; Kusama, Yoshinori
Plasma Physics and Controlled Fusion, 50(4), p.045004_1 - 045004_15, 2008/04
The poloidal polarimeter will be installed in the International Thermonuclear Experimental Reactor (ITER) to measure the safety factor profile. The number of viewing chords is restricted to about 15 channels. Therefore optimization of the viewing chord arrangement is necessary to diagnose the accurate safety factor profile. In this study, we studied the optimum viewing chord arrangement for the equilibria of ITER operation scenarios using the equilibrium reconstruction. For the burning phase of inductive scenario, the error of the safety factor on the magnetic axis was 35% if the viewing chords are not arranged in the peripheral region. It was improved to 3% by arranging the viewing chord of the upper port to peripheral region. This arrangement was used for the reconstruction of the burning phase in the noninductive scenario and of the phase of the plasma current 3.5 MA in the inductive operation scenario. As the result, the accuracy does not decrease drastically.
Okamoto, Masaaki*; Hiraishi, Takehiro*; Ono, Noriyasu*; Takamura, Shuichi*; Nakano, Tomohide; Kawano, Yasunori; Ozeki, Takahisa; Sugihara, Masayoshi
Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00
It is of importance to evaluate the decay time of the plasma current for estimation of the electromagnetic force acting on the vacuum vessel during plasma disruptions in tokamak devices. The L/R model predicts that the decay time is proportional to three-haves power of the electron temperature, indicating the importance of the electron temperature for the estimation. However, it is difficult to measure the electron temperature of the disruptive plasma with the Langmuir probe due to the heat flux and due to the significant electromagnetic force. We propose a measurement technique of the electron temperature by using temperature-sensitive He I lines with high time resolution. In this method, the incident light to a spectrometer is divided into three, each of which transmits a bandpass filter, and then is measured with an absolutely calibrated photo-multiplier. The measured intensity ratios are analyzed with a collisional-radiative model. It is confirmed that the electron temperature determined by this technique is in agreement with that measured by a Langmuir probe in some devices. In the present work, the temporal evolution of the electron temperature during the disruptive plasma of JT-60U is measured with this technique.
Koubiti, M.*; Nakano, Tomohide; Capes, H.*; Marandet, Y.*; Mouret, L.*; Rosato, J.*; Stamm, R.*
Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00
no abstracts in English
Nagashima, Yoshihiko*; Ito, Kimitaka*; Fujisawa, Akihide*; Ito, Sanae*; Yagi, Masatoshi*; Hoshino, Katsumichi; Shinohara, Koji; Ido, Takeshi*; Miura, Yukitoshi; Ejiri, Akira*; et al.
Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00
The recent results on the identification of the outer most magnetic surface and on the identification of the characteristic of the zonal flow are presented by using the measured data of the zonal flow which is a plasma flow in the tokamak plasma. The positon of the outermost magnetic surface was identified using the characteristic of the oscillating zonal flow called as the geodesic acoutic mode (GAM) that the mode exists only in the closed magnetic surface, and the position of the surface was in agreement with that by the magnetic equilibrium reconstruction. Some coincidence with the drift wave - zonal flow theory was obtained by using the finding that the envelope of the density fluctuation of the background turbulence is modulated by the GAM.
C from methane injection into outer divertor plasma in JT-60UNobuta, Yuji; Masaki, Kei; Arai, Takashi; Sakasai, Akira; Miya, Naoyuki; Tanabe, Tetsuo*
Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00
no abstracts in English
Asakura, Nobuyuki; Kawashima, Hisato; Shimizu, Katsuhiro; Sakurai, Shinji; Fujita, Takaaki; Takenaga, Hidenobu; Nakano, Tomohide; Kubo, Hirotaka; Higashijima, Satoru; Hayashi, Takao; et al.
Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00
Divertor design for the JT-60 SA has been progressing in order to handle large heat flux during full pulse duration of 100 s. Divertor should be suitable for single null plasma experiments with the full power injection of 41 MW. The simulation results using 2D fluid (plasma) and Monte-Carlo (neutral) code are summarized. Lower single-null divertor is designed for ITER-like plasma configuration in order to study physics concept of the ITER divertor: control of the plasma detachment. Simulation results for various divertor geometries showed that the vertical target with V-shaped corner can produce plasma detachment near the outer strike-point for medium edge plasma density. It was also demonstrated that the divertor plasma became attached to move the outer strike point above the V-corner, suggesting that recover from sever detachment can be achieved by changing the plasma location. USN divertor will be designed for high-
plasma experiments with the highest shaping plasma of S=6.
5D Vlasov code GT5DIdomura, Yasuhiro; Ida, Masato; Tokuda, Shinji
Europhysics Conference Abstracts (CD-ROM), 31F, 4 Pages, 2007/00
A conservative gyrokinetic toroidal five dimensional Vlasov code GT5D is developed. A conservative finite difference scheme is extended to generalized curvilinear coordinates, and a discretization method is developed so that it exactly satisfies the phase space volume conservation, which is an important feature of the gyrokinetic equaion. In the code, highly accurate and robust long time scale tokamak turbulence simulations in a torus configuration are enabled by these techniques. The code is verified through linear benchmark tests against a toroidal particle code. It is also confirmed that first principles such as the particle number conservation and the energy conservation, which was critical issues in the conventional particle code, are satisfied at high presition.
Aiba, Nobuyuki; Tokuda, Shinji; Ozeki, Takahisa
no journal, ,
In tokamaks, since small aspect ratio makes the magnetic well deeper and increases the magnetic shear, the pressure driven MHD modes become stable. Near the edge pedestal, the edge pedestal pressure gradient can be improved due to accessing to the second stability region of a ballooning mode, and the maximum pressure gradient is restricted by the stability of a peeling-ballooning mode, which depends on not only the pressure gradient but also the amount of the edge current density. Since the stability threshold value of the edge current density hardly depend on the aspect ratio, the lower stability boundary value of the magnetic shear increases as the aspect ratio decreases, and the second stability region becomes narrower. From the viewpoint of the accessibility to the second stability region, we investigate the effect of the aspect ratio on the stability of edge MHD modes, and reveal that the maximum pressure gradient sometimes decreases as the aspect ratio becomes smaller.
Miyato, Naoaki; Kishimoto, Yasuaki; Li, J.*; Tokuda, Shinji
no journal, ,
Finite beta effects on a coupled system of ion temperature gradient (ITG) driven turbulence and zonal modes are investigated by global fluid simulations of electromagnetic ITG turbulence. Finite beta has stabilizing effect on the linear ITG mode, while kinetic ballooning mode (KBM) is destabilized by beta and becomes dominant at high beta. In the ITG dominant regime zonal flows are driven by turbulence via the Reynolds stress and the geodesic transfer is a sink for the zonal flows. The Maxwell stress contribution to zonal flow generation is not so large even at the beta at which the most linearly unstable mode is changing from the ITG mode to the KBM. In electrostatic turbulence simulations, coarse choice of toroidal modes is often used to reduce computational time. But all toroidal modes should be included in numerical turbulence simulations for correct zonal mode generation.
