JOPSS - Search Results

Journal Articles

Observation of the bootstrap current reduction at magnetic island in a neoclassical tearing mode plasma

Oikawa, Toshihiro; Suzuki, Takahiro; Isayama, Akihiko; Hayashi, Nobuhiko; Fujita, Takaaki; Naito, Osamu; Tsuda, Takashi; Kurita, Genichi; JT-60 Team

Nuclear Fusion, 45(9), p.1101 - 1108, 2005/09

https://doi.org/10.1088/0029-5515/45/9/010

Times Cited Count：4 Percentile：14.23(Physics, Fluids & Plasmas)

Evolution of the current density profile associated with magnetic island formation in a neoclassical tearing mode plasma was measured for the first time in JT-60U by. As the island grew, the current density profile turned flat at the radial region of the island, followed by an appearance of a hollow structure. As the island shrank, the deformed region became narrower, and it finally diminished after the disappearance of the island. In an MHD-quiescent plasma, on the other hand, no deformation was observed. The observed deformation in the current density profile associated with the tearing mode is reproduced in a time dependent transport simulation assuming reduction of the bootstrap current in the radial region of the island. Comparison of the measurement with a calculated steady-state solution also explains the temporal behaviors of the current density and safety factor profiles with reduction and recovery of the bootstrap current. From the experimental observation and simulations, we reach conclusion that the bootstrap current decreases within the island O-point.

Journal Articles

Evolution of the current density profile associated with magnetic island formation in JT-60U

Oikawa, Toshihiro; Isayama, Akihiko; Fujita, Takaaki; Suzuki, Takahiro; Tsuda, Takashi; Kurita, Genichi

Physical Review Letters, 94(12), p.125003_1 - 125003_4, 2005/04

https://doi.org/10.1103/PhysRevLett.94.125003

Times Cited Count：10 Percentile：53.4(Physics, Multidisciplinary)

Evolution of the current density profile associated with the magnetic island formation during a tearing mode was measured for the first time in the JT-60U tokamak. With the island growth, the current density profile turned flat at the radial region of the island, followed by appearance of a hollow structure. As the island shrank, the flat region became narrower, and it finally diminished after disappearance of the island. It was also observed that the local poloidal magnetic field fluctuated in correlation with the island rotation. This indicates that the observed deformation in the current density profile is localized in the O-point of the island. The result is the first experimental demonstration of theoretical predictions on the current density evolution in tearing modes.

Journal Articles

External feedback effect on magnetic islands in tokamaks

Konovalov, S. V.; Mikhailovskii, A. B.*; Kovalishen, E. A.*; Kamenets, F. F.*; Ozeki, Takahisa; Shirokov, M. S.*; Takizuka, Tomonori; Tsypin, V. S.*

Doklady Physics, 49(7), p.405 - 408, 2004/07

https://doi.org/10.1134/1.1784852

Times Cited Count：1 Percentile：11.77(Mechanics)

Effect of feedback system, placed outside the vacuum vessel, on neoclassical tearing modes (NTMs) in tokamaks is analytically studied. External matching parameters for magnetic island chain are derived for the simplest case of step profile of equilibrium parallel current. The structure of dynamical equations for the island width and island rotation frequency in terms of matching parameters is explained. It is shown that such a feedback system can lead to essential shift of the island rotation, in particular, for stabilization of NTMs by the polarization current effect.

Journal Articles

Microislands in tokamaks

Mikhailovskii, A. B.*; Kovalishen, E. A.*; Shirokov, M. S.*; Konovalov, S. V.; Tsypin, V. S.*; Kamenets, F. F.*; Ozeki, Takahisa; Takizuka, Tomonori

Physics of Plasmas, 11(2), p.666 - 676, 2004/02

https://doi.org/10.1063/1.1640377

Times Cited Count：6 Percentile：20(Physics, Fluids & Plasmas)

Analytical treatment of magnetic islands with high poloidal mode numbers and widths smaller than ion Larmor radius (microislands) is presented. The profile functions and rotation frequencies of microislands are investigated with the two-fluid magnetohydrodynamics. The microislands are described in terms of two profile functions, one of which characterizes the electric field and perturbed plasma density, and second the perturbed electron temperature. The problem of rotation frequencies of microislands is discussed.

Journal Articles

Effects of parallel viscosity on rotation of magnetic islands in tokamaks

Konovalov, S. V.; Mikhailovskii, A. B.*; Tsypin, V. S.*; Kovalishen, E. A.*; Shirokov, M. S.*; Ozeki, Takahisa; Takizuka, Tomonori

Physics Letters A, 318(4-5), p.429 - 434, 2003/11

https://doi.org/10.1016/j.physleta.2003.09.045

Times Cited Count：7 Percentile：46.48(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Axisymmetric tri-magnetic-islands equilibrium of strongly-reversed-shear tokamak plasma; An Idea for the current hole

Takizuka, Tomonori

Purazuma, Kaku Yugo Gakkai-Shi, 78(12), p.1282 - 1284, 2002/12

http://ci.nii.ac.jp/naid/130000133603

An idea of a new equilibrium of a strongly-reversed-shear tokamak plasma with a current hole is proposed. This equilibrium configuration called "Axisymmetric Tri-Magnetic-Islands (ATMI) equilibrium" has three islands, a central-negative-current island and side-positive-current islands, along the R direction and two x-points along the Z direction. The equilibrium is stable with the elongation coils when the current in the ATMI region is limited small.

Journal Articles