Dynamics of ion internal transport barrier in LHD heliotron and JT-60U tokamak plasmas

Ida, K.; Sakamoto, Y.; Yoshinuma, M.; Takenaga, H.; Nagaoka, K.; Hayashi, Naoki; Oyama, N.; Osakabe, M.; Yokoyama, M.; Funaba, H.; Tamura, N.; Tanaka, Kaoru; Takeiri, Y.; Ikeda, K.; Tsumori, K.; Kaneko, O.; Itoh, K.; Inagaki, S.; Kobuchi, T.; Isayama, A.; Suzuki, Takahiro; Fujita, T.; Matsunaga, G.; Shinohara, K.; Koide, Y.; Yoshida, M.; Ide, S.; Kamada, Y.

doi:10.1088/0029-5515/49/9/095024

Cited by 37 publications

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References 26 publications

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“…For example, the transition from L-mode to the H-mode is observed in the narrow window of rotational transform near but not at the loworder rational magnetic surface in helical plasmas [10]. In tokamak plasmas, the propagation of the internal transport barrier foot point stops at low-order rational surfaces [11], whereas a significant improvement of transport is observed inside a magnetic island [12]. This is because of the complex interplay between transport and sheared radial electric field, which contributes to the reduction of turbulence-driven transport in the proximity of rational surfaces [13].…”

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confidence: 98%

Topology bifurcation of a magnetic flux surface in magnetized plasmas

et al. 2013

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Bifurcation phenomena in the radial propagation of a heat pulse driven by modulated electron cyclotron heating are observed in the Large Helical Device. There are two patterns of heat pulse propagation observed in the flat temperature region. One is a bi-directional slow heat pulse propagation observed in the fast magnetic shear drop and the other is a fast heat pulse propagation observed in the slow magnetic shear drop. This bifurcation in the heat pulse propagation suggests the topology bifurcation of a magnetic flux surface in the plasma.The transition from regular to chaotic motion is very often represented as a topological bifurcation of a torus in phase space [1]. Islands are formed in nested tori by resonant perturbations, and if global stochasticity sets in, turbulence-driven transport (such as superdiffusion) can occur [2]. This topological bifurcation has been considered to happen in hightemperature toroidal plasmas, e.g. during disruption in tokamaks [3,4], by a large deformation such as a spontaneous transition from the stochastic state to helical equilibrium in reversed-field pinch (RFP) plasmas [5][6][7], or at the plasma edge as seen in the edge-localized-modes mitigation

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confidence: 98%

Topology bifurcation of a magnetic flux surface in magnetized plasmas

et al. 2013

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“…Bifurcation phenomena in the ion heat transport were found before the finding of electron ITB in many tokamak plasmas [68][69][70][71][72][73][74][75][76][77][78] and in helical plasmas [79][80][81][82][83][84][85] (see review [59]). The formation of internal transport barrier in the ion heat transport (ion ITB) is somewhat slower than the electron ITB because this bifurcation is not triggered by the rapid change in the radial electric field.…”

Section: Itb Formation In Ion Heat Transportmentioning

confidence: 98%

Bifurcation phenomena in magnetically confined toroidal plasmas

Ida

2020

Advances in Physics: X

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Bifurcation phenomena observed in turbulence and transport, in topology of magnetic field and MHD, and the interplay between turbulence and MHD bifurcation in magnetically confined toroidal plasmas are reviewed. Two types of bifurcation phenomena in turbulent transport are discussed. One is significant change in the magnitude of the diffusion term and the other is a sign flip of non-diffusive term of transport. The bifurcation of diffusion term magnitude causes the transition to a so-called improved mode such as ion-electron root transition, L-mode to H-mode transition, and ITB formation. In contrast, the bifurcation of non-diffusion term sign causes the intrinsic flow reversal, convection reversal of bulk ion, and impurity ions. Two types of bifurcation phenomena in MHD are discussed. One is the bifurcation of static magnetic topology and the other is the bifurcation of MHD instability. The bifurcation of static magnetic topology is observed in between three magnetic topology (nested magnetic flux surface, magnetic island and stochastic magnetic field) in toroidal plasma. The bifurcation of MHD instability is observed as a parity change of MHD oscillation. The bifurcation of the magnetic island states caused by the interplay between turbulence and MHD is also discussed.

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“…In the Large Helical Device (LHD), the ion ITB appears when the positive ion source neutral beam (P-NB) is injected before the negative ion source neutral beam (N-NB) but not when the N-NB is injected before the P-NB, even if the total heating power is identical later in the discharge [7][8][9][10]. The T e /T i ratio at the time when both P-NB and N-NB are injected is larger in the discharges with prior N-NBI rather than the discharges with prior P-NBI.…”

Section: Introductionmentioning

confidence: 99%

“…Radial profiles of (a) ion temperature, electron temperature and electron density in the plasma with ion ITB in LHD, (b) ion temperature and radial electric field and (c) ion thermal diffusivity at t = 2.10 sec (in the L-mode phase) and t = 2.34 sec (in the steady-state phase of ITB) (Fig. (c)from Ref[7] modified). (Colorfigure:www.cpp-journal.org).…”

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Ion Internal Transport Barrier in the Large Helical Device

Ida

Yoshinuma

Nagaoka

et al. 2010

Contrib. Plasma Phys.

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The internal transport barrier (ITB) appears in ion root plasmas with NBI heating ,when the T e/Ti ratio is held below unity in LHD. The improvement of transport is observed only in the ion heat transport, not in the electron heat transport nor in the particle transport. During the formation of ion ITB, the region of low ion thermal diffusivity expands toward the plasma center and results in a wide weak ITB, which is in contrast to the narrow strong ITB typically observed in tokamaks.

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Dynamics of ion internal transport barrier in LHD heliotron and JT-60U tokamak plasmas

Cited by 37 publications

References 26 publications

Topology bifurcation of a magnetic flux surface in magnetized plasmas

Topology bifurcation of a magnetic flux surface in magnetized plasmas

Bifurcation phenomena in magnetically confined toroidal plasmas

Ion Internal Transport Barrier in the Large Helical Device

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