JOPSS - Search Results

Journal Articles

Roles of the double tearing mode on the formation of a current hole

Tsuda, Takashi; Kurita, Genichi; Fujita, Takaaki

Journal of Plasma Physics, 72(6), p.1149 - 1152, 2006/12

https://doi.org/10.1017/S0022377806005824

Times Cited Count：3 Percentile：10.78(Physics, Fluids & Plasmas)

The current density is expected to be negative in the central region of the tokamak when the amplitude of bootstrap current or off-axis current drive is large enough and a negative one-turn voltage exists. However, a flat current profile with almost zero value has been observed in experiments. The current profile with Current Hole has a tendency to be unstable to double tearing mode and we investigate the role of double tearing mode on the formation of Current Hole with RMHD simulation.

Journal Articles

Stability of double tearing mode in current hole configuration

Tsuda, Takashi; Kurita, Genichi; Fujita, Takaaki

Journal of the Korean Physical Society, 49, p.S83 - S86, 2006/12

The current density is expected to be negative in the central region of the tokamak when the amplitude of bootstrap current or off-axis current drive is large enough. However, a flat current profile with almost zero value has been observed in experiments even under the situation with negative one-turn voltage exists in the central region of plasma. Double tearing mode (DTM) can be unstable for the current profile with a "current hole" and some MHD activities are observed in JET before the formation of the current hole. On the contrary, no MHD activity is observed in the JT-60 experiment. Here, we study the condition of appearance of DTM and investigate the stability of DTM and the interaction between DTM (n=1 perturbation) and "Current Hole" with resistive RMHD simulations.

Journal Articles

Nonlinear behaviour of collisionless double tearing mode induced by electron inertia

Matsumoto, Taro; Naito, Hiroshi*; Tokuda, Shinji; Kishimoto, Yasuaki*

Nuclear Fusion, 45(11), p.1264 - 1270, 2005/11

https://doi.org/10.1088/0029-5515/45/11/006

Times Cited Count：14 Percentile：43.63(Physics, Fluids & Plasmas)

A gyrokinetic particle simulation is executed to clarify the effect of the electron inertia on the MHD phenomena in the reversed shear configuration (RSC) of a cylindrical tokamak plasma. It is found that the collisionless (kinetic) double tearing modes grow up at the Alfvn time scale, and nonlinearly induce the internal collapse when the helical flux at the magnetic axis is less than that at the outer resonant surface. After the internal collapse, the secondary reconnection is induced by the current concentration due to the convective flow. It is also clarified that a nonlinear dynamics accompanied with the elementary processes caused by the flow can generate a new RSC with resonant surfaces. In the presence of the density gradient, after the full reconnection induced by the mode, the radial electric field is found to be generated due to the difference of the motion between ions and electrons. However, the intensity of the radial field is not so large as that induced by the collisionless kink mode.

Journal Articles

Nonlinear acceleration of the electron inertia-dominated magnetohydrodynamic modes due to electron parallel compressibility

Matsumoto, Taro; Naito, Hiroshi*; Tokuda, Shinji; Kishimoto, Yasuaki

Physics of Plasmas, 12(9), p.092505_1 - 092505_7, 2005/09

https://doi.org/10.1063/1.2042167

Times Cited Count：2 Percentile：6.86(Physics, Fluids & Plasmas)

The behavior of the collisionless magnetohydrodynamics modes is investigated by the gyro-kinetic particle simulation in a cylindrical tokamak plasma in the parameter region where the effects of electron inertia and electron parallel compressibility are competitive for magnetic reconnection. Although the linear growth of the internal kink-tearing mode is dominated by the electron inertia, it is found that the growth rate can be nonlinearly accelerated due to the electron parallel compressibility proportional to the ion sound Larmor radius . It is also found that, as decreasing the electron skin depth , the maximum growth rate before the internal collapse saturates independently of the microscopic scales such as and . The acceleration of growth rate is also observed in the nonlinear phase of the double tearing mode.

Journal Articles

Advances in plasma and fusion simulation and prospects for the future; From a viewpoint of magnetically confined fusion

Kishimoto, Yasuaki

Purazuma, Kaku Yugo Gakkai-Shi, 80(5), p.390 - 395, 2004/05

https://doi.org/10.1585/jspf.80.390

High performance magnetically confined plasma is realized by having structures in plasmas, where different elementary processes with different time and spatial scales are deeply contributing with each other. A research based on large scale simulation is then essential to understand such hierarchical complex plasmas. We discuss the underlying physical process of the structural plasma and present a prospect for future numerical simulations covering a wide dynamical range.

Journal Articles

Generation of radial electric field induced by collisionless internal kink mode with density gradient

Matsumoto, Taro; Tokuda, Shinji; Kishimoto, Yasuaki; Naito, Hiroshi*

Physics of Plasmas, 10(1), p.195 - 203, 2003/01

https://doi.org/10.1063/1.1528608

Times Cited Count：5 Percentile：16.93(Physics, Fluids & Plasmas)

Effects of density gradient on the collisionless m=1 internal kink mode in a cylindrical tokamak plasma are studied by the gyro-kinetic particle simulations. When the density gradient is not large enough to change the full reconnection process, the phenomena after the full reconnection, such as the secondary reconnection and the evolution of the safety factor profile, are changed considerably due to the self-generated radial electric field, i.e. the m=0 mode. The growing mechanism is explained by the difference of drift motion between ions and electrons, which is caused by the fast parallel motion of electron. Once the radial electric field is triggered by the symmetrical flow induced by the m=1 mode, the m=0 mode grows up to the same level as the m=1 mode, and drives an plasma rotation in the ion diamagnetic direction, which breaks the symmetrical plasma flow induced by the m=1 mode. The density and current distributions, and minimum safety factor after the full reconnection, are found to be affected by the asymmetrical flow driven by the m=1 and m=0 modes.