High-β tokamaks?

Wesson, John

doi:10.1038/272017a0

Cited by 158 publications

(310 citation statements)

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“…Plasmas are confined in tokamaks by magnetic field lines on nested axisymmetric toroidal magnetic surfaces. 1 This occurs for both conventional tokamaks, with an inductive plasma current density with a maximum at the centre, 1 and in tokamaks with a non-inductive current density with a maximum outside the centre, as presently in JET 2,3 and predicted in the forthcoming ITER. 4 However, some advanced confinement regimes with non inductive currents develop a radial hollow current profile, with a central hole where the current density is almost zero or even negative.…”

mentioning

confidence: 77%

“…This expansion has some peculiarities due to the considered reversed current density. Namely, we consider the expansion for w 0 ðr t Þ up to the second order approximation and the expansion for w 1 …”

Section: Phys Plasmas 18 082508 (2011)mentioning

confidence: 99%

“…5 Whenever a reversed current density is created, the magnetic surfaces are non-nested with magnetic islands since a magnetic field component normal to the average magnetic surface is generated. 5,6 As this new configuration with current hole opens a new regime to be explored in tokamaks, 5 it is useful to know solutions of the Grad-Shafranov equation 1 which describe magnetohydrodynamic (MHD) equilibria with non nested magnetic surfaces.…”

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confidence: 99%

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Analytical solutions for Tokamak equilibria with reversed toroidal current

et al. 2011

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In tokamaks, an advanced plasma confinement regime has been investigated with a central hollow electric current with negative density which gives rise to non-nested magnetic surfaces. We present analytical solutions for the magnetohydrodynamic equilibria of this regime in terms of non-orthogonal toroidal polar coordinates. These solutions are obtained for large aspect ratio tokamaks and they are valid for any kind of reversed hollow current density profiles. The zero order solution of the poloidal magnetic flux function describes nested toroidal magnetic surfaces with a magnetic axis displaced due to the toroidal geometry. The first order correction introduces a poloidal field asymmetry and, consequently, magnetic islands arise around the zero order surface with null poloidal magnetic flux gradient. An analytic expression for the magnetic island width is deduced in terms of the equilibrium parameters. We give examples of the equilibrium plasma profiles and islands obtained for a class of current density profile.

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confidence: 77%

Section: Phys Plasmas 18 082508 (2011)mentioning

confidence: 99%

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confidence: 99%

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Analytical solutions for Tokamak equilibria with reversed toroidal current

et al. 2011

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“…with the resistivity factor N ðZ eff Þ [3]. The term C M is much smaller than C I and can be neglected for the following considerations.…”

Section: à0:73mentioning

confidence: 99%

Density limits in helium plasmas at JET

Rapp

Huber

Ingesson

et al. 2003

Journal of Nuclear Materials

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Recently at JET a pure helium campaign has been performed. The exploration of the density limit in L-mode limiter as well as L-mode and H-mode diverted plasmas was one of the main objectives. In L-mode plasmas the density can be increased until the total radiated power equals the heating power, hence the density limit is determined by a radiative collapse. When compared to deuterium plasmas the L-mode density limit in helium is twice as high. In H-mode no significant difference in the density limit process has been observed. The pedestal density just before the H to L-mode back transition is the same in deuterium and helium plasmas. The H to L-mode back transition is followed by a development of a MARFE [J. Nucl. Mater. 145-147 (1987) 15] which eventually leads to a density limit disruption.

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“…This process takes place in the current sheet formed at the boundary between opposed magnetic fields and is thought to play an important role in space phenomena, such as solar flares 4 and at Earth's magnetosphere 5 , as well as in fusion experiments 6,7 . Despite intense research on the topic over the last decades and a vast quantity of information obtained through space observations 8,9 , numerical simulations 10,11 and experiments [12][13][14][15][16][17][18][19] , the underlying processes of magnetic reconnection are still not fully understood.…”

Section: Introductionmentioning

confidence: 99%

VINETA II: A linear magnetic reconnection experiment

Bohlin

Stechow

Grulke

et al. 2014

Review of Scientific Instruments

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A linear experiment dedicated to the study of driven magnetic reconnection is presented. The new device (VINETA II) is suitable for investigating both collisional and near collisionless reconnection. Reconnection is achieved by externally driving magnetic field lines towards an X-point, inducing a current in the background plasma which consequently modifies the magnetic field topology. Owing to the open field line configuration of the experiment, the current is limited by the axial sheath boundary conditions. A plasma gun is used as an additional electron source in order to counterbalance the charge separation effects and supply the required current. Two drive methods are used in the device. First, an oscillating current through two parallel conductors drive the reconnection. Second, a stationary X-point topology is formed by the parallel conductors, and the drive is achieved by an oscillating current through a third conductor. In the first setup, the magnetic field of the axial plasma current dominates the field topology near the X-point throughout most of the drive. The second setup allows for the amplitude of the plasma current as well as the motion of the flux to be set independently of the X-point topology of the parallel conductors. a) hannes.bohlin@ipp.mpg.de

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High-β tokamaks?

Cited by 158 publications

References 0 publications

Analytical solutions for Tokamak equilibria with reversed toroidal current

Analytical solutions for Tokamak equilibria with reversed toroidal current

Density limits in helium plasmas at JET

VINETA II: A linear magnetic reconnection experiment

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