Electron thermal transport in RTP: filaments, barriers and bifurcations

Cardozo, N.J. Lopes; Hogeweij, G. M. D.; Baar, M. de; Barth, Clemens; Beurskens, M.; Luca, F. De; Donné, A. J. H.; Galli, P.; Gelder, J. F. M. van; Gorini, G.; Groot, B. de; Jacchia, A.; Karelse, F. A.; Kloe, Jos de; Kruijt, O.G.; Lok, J.; Mantica, P.; Meiden, H.J. van der; Oomens, A.A.M.; Oyevaar, T.; Pijper, F. J.; Polman, R.W.; Salzedas, F.; Schüller, F. C.; Westerhof, E.

doi:10.1088/0741-3335/39/12b/023

Cited by 121 publications

(99 citation statements)

References 13 publications

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“…They conclude that this phenomenon is caused by the idea that the rational magnetic surfaces, particularly the qϭ1 surface, should work as the thermal transport barrier for electron. 76 In the magnetic configuration of the CHS, the safety factor monotonically decreases toward the periphery, and the rational values are q(0.27)ϭ3/1, q(0.46)ϭ5/2 and q(0.63)ϭ2/1. The strongest barrier of qϭ1 in the RTP case is out of the plasma boundary in the CHS configuration.…”

Section: Bifurcation and Transport Barriermentioning

confidence: 92%

“…The edge transport barrier in the H-mode is located near the separatrix. Recent experiments in the ECR-discharges of the Rijnhuizen Tokamak Project ͑RTP͒ have also shown a discrete change in the electron temperature profiles together with its central value, 76,77 according to the radius of the electron cyclotron resonance. They conclude that this phenomenon is caused by the idea that the rational magnetic surfaces, particularly the qϭ1 surface, should work as the thermal transport barrier for electron.…”

Section: Bifurcation and Transport Barriermentioning

confidence: 97%

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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: 92%

Section: Bifurcation and Transport Barriermentioning

confidence: 97%

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

et al. 2000

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“…These plasmas were centrally heated by means of ECH. There is a much smaller set of observations of filaments in plasmas with inverted q profiles, which in RTP are obtained-steady state-by application of off-axis ECH [19,20,21]. Figure 9 gives an example of an extreme case, where the ECH resonance was at ρ = 0.6 (corresponding to z = 100 mm).…”

Section: Do Filaments Occur At Q > 1?mentioning

confidence: 99%

Filamentation in the RTP tokamak plasma

Beurskens¹,

Cardozo

Arends

et al. 2000

Plasma Phys. Control. Fusion

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Experimental data are presented showing filamentation of the Rijnhuizen tokamak project (RTP) plasma. These filaments are only resolved by the highresolution double pulse Thomson scattering diagnostic, and appear as multiple peaks in the T e profile with a typical width of 5-10 mm and an amplitude as high as 1 keV in a 2 keV ambient plasma. This paper shows the occurrence of filaments under various plasma conditions. It shows that filaments are statistically significant plasma physical phenomena. A parameter study shows a weak dependence of their amplitude on q a , whereas a strong inverse dependence on plasma density has been found. It takes filaments several milliseconds to develop after the switch-on of electron cyclotron heating; they are wiped out by a sawtooth crash and take only a few hundred microseconds to reappear after such a crash. They mainly occur in the centre of additionally heated plasmas by means of electron cyclotron heating, but have also been observed in transiently heated plasmas and off-axis in non-centrally heated plasmas. Finally, two interpretations of filament topology are tested by means of three experiments. It turns out that the interpretation of filaments as independent closed tube-like structures seems to best fit the RTP data.

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“…Our interest is toward what happens to these vacuum magnetic configurations when plasma is produced. Although the exact magnetic configuration is difficult to measure directly with the presently available diagnostics, we may infer the state of a magnetic configuration from the fine-spatial profile of electron temperature (T e ), which is supposed to be constant along a magnetic field line, as was demonstrated in tokamaks [13,14]: If a T e profile has a flat region or a bump near a rational surface, this probably implies an island, though the possibility of a very local heating or a local transport anomaly cannot be ruled out. The Thomson scattering system [15] installed on LHD was designed to repetitively measure T e and electron density (n e ) at 200 positions along the major radius on the Z 0 plane at the horizontally elongated section.…”

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confidence: 99%

Observation of the “Self-Healing” of an Error Field Island in the Large Helical Device

Narihara¹,

Watanabe²,

Yamada³

et al. 2001

Phys. Rev. Lett.

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It was observed that the vacuum magnetic island produced by an external error magnetic field in the large helical device shrank in the presence of plasma. This was evidenced by the disappearance of flat regions in the electron temperature profile obtained by Thomson scattering. This island behavior depended on the magnetic configuration in which the plasmas were produced. DOI: 10.1103/PhysRevLett.87.135002 PACS numbers: 52.55.HcExistence of a set of nested magnetic surfaces (magnetic configuration) is a prerequisite for almost all toroidal magnetic confinement devices [1]. In the tokamak, a magnetic configuration is generated by plasma current plus external coil currents, and hence the concept of a vacuum magnetic configuration does not exist. On the other hand, the stellarator, by its definition, possesses a vacuum magnetic configuration that is able to confine plasma just as Nature possesses a vacuum space-time that allows the existence of matter. This fact makes it easier in the stellarator than in the tokamak to study the interactions between the magnetic configuration and plasma such as the formation of topological defects and their reactions on the plasma behavior. The vacuum magnetic configuration of a stellarator is inevitably accompanied by topological defects such as magnetic islands and stochastic regions as a result of a weak violation of a helical symmetry. If these defects are large in size or numerous, they will deteriorate the plasma confinement considerably. This was a central issue in stellarator development. However, nowadays, we can make these topological defects small enough not to degrade the plasma confinement over a wide region by optimizing the coil-winding law [2]. Although the vacuum magnetic configuration problem was thus solved, the question whether a fairly good magnetic configuration is preserved in the presence of plasma has not yet been settled. Cary and Kotschenreuther [3] showed that sharply peaked currents near the island enhance or limit the island size, depending on whether the average curvature is bad or good. They also showed that in the hill region the islands overlap for arbitrary small beta b (kinetic pressure/magnetic pressure). Hegna and Bhattacharjee [4] generalized the above statement for higher b plasma with the result that the well/hill criterion should be replaced by the resistive interchange stability criterion. Hayashi et al. [5] computationally found that the vacuum magnetic surfaces of an L 2͞M 10 heliotron/torsatron configuration are, indeed, broken at high b, giving a more stringent limit on b than that imposed by equilibrium. Hayashi et al. [6] also discovered that as b increases the islands present in the vacuum heliac configuration diminish ("self-heal") and then reappear with the flipped phase at a higher b. Bhattacharjee et al. [7] formulated a theory to explain the above "self-healing" phenomenon. Hegna [8] further generalized the above theories to incorporate the effect of a bootstrap current. Since these theoretical and numerical predictions hav...

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Electron thermal transport in RTP: filaments, barriers and bifurcations

Cited by 121 publications

References 13 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

Filamentation in the RTP tokamak plasma

Observation of the “Self-Healing” of an Error Field Island in the Large Helical Device

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