Operational conditions and characteristics of ELM-events during H-mode plasmas in the stellarator W7-AS

Hirsch, M.; Grigull, P.; Wobig, H.; Kißlinger, J.; McCormick, K.; Anton, M.; Baldzuhn, J.; Fiedler, S.; Fuchs, C.; Geiger, J.; Giannone, L.; Hartfuß, H. J.; Holzhauer, E.; Jaenicke, R.; Kick, M.; Maaßberg, H.; Wagner, F.; Weller, A.; Team, W As

doi:10.1088/0741-3335/42/5a/327

Cited by 35 publications

(31 citation statements)

References 3 publications

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“…Proper ELMs and H-modes are only observed in W7-AS with the ι a -value in certain operational windows [27]. The fact that the correlations we have discovered for bad confinement are akin to those identified in L-mode suggests that the term 'ELM-like' is a good label for these turbulent bursts.…”

Section: A Confinement and Correlated Fluctuationsmentioning

confidence: 54%

Study of intermittent small-scale turbulence in Wendelstein 7-AS plasmas during controlled confinement transitions

Basse

Zoletnik²,

Michelsen³

et al. 2005

Physics of Plasmas

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Section: A Confinement and Correlated Fluctuationsmentioning

confidence: 54%

Study of intermittent small-scale turbulence in Wendelstein 7-AS plasmas during controlled confinement transitions

Basse

Zoletnik²,

Michelsen³

et al. 2005

Physics of Plasmas

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“…Furthermore, the impact of magnetic topology on confinement has been found to be significantly large in toroidal plasmas. 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].…”

mentioning

confidence: 97%

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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“…In stellarator H-modes the energy confinement is enhanced modestly (no more than 30%) in W7-AS [15,16] and CHS [53,54,55,56]. Access is typically restricted to narrow ranges ini that minimize damping of poloidal rotation at the plasma boundary by avoiding island chains [57,58] (in W7-AS toroidal rotation is strongly damped by toroidal mirrors, but poloidal rotation is possible).…”

Section: Enhanced Confinement Regimes In Stellaratorsmentioning

confidence: 99%

Assessment of Transport in NCSX

Mikkelsen

Maaßberg

Zarnstorff

et al. 2007

Fusion Science and Technology

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We explore whether the energy confinement and planned heating in NCSX are sufficient to test MHD stability limits, and whether the configuration is sufficiently quasi-axisymmetric to reduce the neoclassical ripple transport to low levels, thereby allowing tokamak-like transport. A 0-D model with fixed profile shapes is related to global energy confinement scalings for stellarators and tokamaks; neoclassical transport properties are assessed with the DKES, NEO, and NCLASS codes; and a power balance code is used to predict temperature profiles. Reaching the NCSX goal of =4% at low collisionality will require H_ISS-95=3, which is higher than the best achieved in present stellarators. However, this level of confinement is actuallỹ 10% lower than that predicted by the ITER-97P tokamak L-mode scaling. By operating near the stellarator density limit, the required H_ISS-95 is reduced by 35%. The high degree of quasiaxisymmetry of the configuration and the self-consistent 'ambipolar' electric field reduce the neoclassical ripple transport to a small fraction of the neoclassical axisymmetric transport. A combination of neoclassical and anomalous transport models produces pressure profile shapes that are within the range of those used to study the MHD stability of NCSX. We find that =4% plasmas are 'neoclassically accessible', and are compatible with large levels of anomalous transport in the plasma periphery. 7-2

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Operational conditions and characteristics of ELM-events during H-mode plasmas in the stellarator W7-AS

Cited by 35 publications

References 3 publications

Study of intermittent small-scale turbulence in Wendelstein 7-AS plasmas during controlled confinement transitions

Study of intermittent small-scale turbulence in Wendelstein 7-AS plasmas during controlled confinement transitions

Topology bifurcation of a magnetic flux surface in magnetized plasmas

Assessment of Transport in NCSX

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