Radial Electric Field Measurements in Reversed Shear Plasmas

Levinton, F. M.; Bell, R. E.; Batha, S. H.; Synakowski, E. J.; Zarnstorff, M. C.

doi:10.1103/physrevlett.80.4887

Cited by 60 publications

(36 citation statements)

References 30 publications

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“…66 Similar bifurcation mechanisms are proposed for the formation of the internal transport barrier. 67,68 The recent experimental results of the internal transport barrier 69,70 also support that the formation mechanism of the internal transport barrier should be ascribed to the bifurcation of the radial electric field, as is the case of the edge transport barrier. 8,9 In the CHS experiments, the thermal transport barrier for electrons is formed around the core when a rather strong ECR-heating is applied with on-axis resonance.…”

Section: Bifurcation and Transport Barriermentioning

confidence: 76%

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

et al. 2000

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The bifurcation nature of the electrostatic structure is studied in the toroidal helical plasma of the Compact Helical System ͑CHS͒ ͓K. Matsuoka et al., Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, 1988 ͑International Atomic Energy Agency, Vienna, 1989͒, Vol. 2, p. 411͔. Observation of bifurcation-related phenomena is introduced, such as characteristic patterns of discrete potential profiles, and various patterns of self-sustained oscillations termed electric pulsation. Some patterns of the electrostatic structure are found to be quite important for fusion application owing to their association with transport barrier formation. It is confirmed, as is shown in several tokamak experiments, that the thermal transport barrier is linked with electrostatic structure through the radial electric field shear that can reduce the fluctuation resulting in anomalous transport. This article describes in detail spatio-temporal evolution during self-sustained oscillation, together with correlation between the radial electric field and other plasma parameters. An experimental survey to find dependence of the temporal and spatial patterns on plasma parameters is performed in order to understand systematically the bifurcation property of the toroidal helical plasma. The experimental results are compared with the neoclassical bifurcation property that is believed to explain the observed bifurcation property of the CHS plasmas. The present results show that the electrostatic property plays an essential role in the structural formation of toroidal helical plasmas, and demonstrate that toroidal plasma is an open system with a strong nonlinearity to provide a new attractive problem to be studied.

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Section: Bifurcation and Transport Barriermentioning

confidence: 76%

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

et al. 2000

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“…The turbulence-suppression criterion was found to be satisfied in tokamak plasmas just prior to the L-H transition and in H-mode [10,11,14], and also in internal transport barriers maintained via E × B shear primarily resulting from toroidal or poloidal ion rotation [16][17][18]. L-H transitions exhibiting LCO are particularly well suited to uncover the dynamics of shear-flow decorrelation due to the slow transition timescale.…”

Section: Shear Decorrelationmentioning

confidence: 99%

“…It was recognized early on that the H-mode edge barrier forms as fluctuations are suppressed due to E × B flow shear [9][10][11] in a narrow (few cm wide) radial layer just inside the last closed flux surface (LCFS) [12][13][14][15]. While the paradigm of flow-shear suppression has been experimentally verified in the H-mode edge transport barrier as well as in internal transport barriers [16][17][18], the sequence of events leading to the formation of a highly sheared E × B jet flow layer has been the subject of intensive research. In particular, the causality of shear layer formation and pressure-gradient increase has been under investigation in many different toroidal confinement devices.…”

Section: Introductionmentioning

confidence: 99%

The role of turbulence–flow interactions in L- to H-mode transition dynamics: recent progress

Schmitz

2017

Nucl. Fusion

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This scaling reflects only the dependence of the L-H transition power threshold on plasma density ) − n (10 m e 203 , toroidal magnetic field φ B (T), and the plasma surface area S (m 2 ). However, the threshold power has been shown to depend on additional parameters such as isotopic plasma composition, plasma shape, divertor geometry, and the beam-induced and intrinsic torque [4][5][6][7][8]. A physics-based model of the L-H transition threshold power is therefore needed to confidently extrapolate to auxiliary heating requirements for ITER and future burning plasma experiments. It was recognized early on that the H-mode edge barrier forms as fluctuations are suppressed due to E × B flow shear [9][10][11] in a narrow (few cm wide) radial layer just inside the last closed flux surface (LCFS) [12][13][14][15]. While the paradigm of Nuclear Fusion

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“…In addition, the motional Stark effect (MSE) diagnostic for the poloidal magnetic field was expanded to measure the radial electric field directly [27]. With these new capabilities supplementing the existing diagnostics, measurements were ultimately made of all terms in the radial force balance for the carbon impurities.…”

Section: Transport Barriers In Tftr Plasmas With Reversed Shearmentioning

confidence: 99%

Core Transport Reduction in Tokamak Plasmas with Modified Magnetic Shear

Bell¹,

Bell²,

Efthimion³

et al. 1998

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Spontaneous improvements of plasma confinement during auxiliary heating have been observed in many tokamaks when the q profile has been modified from its normal resistive equilibrium so that q > 1 and the magnetic shear is reduced or reversed in a region near the magnetic axis. The effects on the overall plasma confinement result from the formation in the plasma interior of transport barriers, regions where the thermal and particle transport coefficients are substantially reduced.These internal barriers are sometimes tied to unique magnetic surfaces, such as the surface where the shear reverses. The reduction in transport appears to result from the suppression of turbulence by sheared plasma flow, which has now been measured in TFTR. Extensions of the theory for turbulence suppression show that this underlying paradigm may also explain other regimes of improved core confinement. The excitement generated by these discoveries must be tempered by the realization that transport and stability to pressure-driven MHD instabilities are intimately linked in these plasmas through the bootstrap current and the effect of the resulting current profile on the transport. Thus the development of control tools and strategies is essential if these improved regimes of confinement are to be exploited to improve the prospects for fusion energy production.

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Radial Electric Field Measurements in Reversed Shear Plasmas

Cited by 60 publications

References 30 publications

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

Experimental study of the bifurcation nature of the electrostatic potential of a toroidal helical plasma

The role of turbulence–flow interactions in L- to H-mode transition dynamics: recent progress

Core Transport Reduction in Tokamak Plasmas with Modified Magnetic Shear

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