Regime of Improved Confinement and High Beta in Neutral-Beam-Heated Divertor Discharges of the ASDEX Tokamak

Wagner, F.

doi:10.1103/physrevlett.49.1408

Cited by 2,005 publications

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“…At about the same time, two unexpected discoveries were made on tokamaks with the poloidal divertors: the H-mode with improved core plasma confinement (Wagner et al 1982) and the high-recycling regime of divertor plasma performance (see Keilhacker et al (1982), Lackner et al (1984) and the references therein), both of which became phenomena of prime interest for the magnetic fusion scientists.…”

Section: Introductionmentioning

confidence: 99%

Physics of ultimate detachment of a tokamak divertor plasma

Krasheninnikov¹,

2017

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The basic physics of the processes playing the most important role in divertor plasma detachment is reviewed. The models used in the two-dimensional edge plasma transport codes that are widely used to address different issues of the edge plasma physics and to simulate the experimental data, as well as the numerical schemes and convergence issues, are described. The processes leading to ultimate divertor plasma detachment, the transition to and the stability of the detached regime, as well as the impact of the magnetic configuration and divertor geometry on detachment, are considered. A consistent, integral physical picture of ultimate detachment of a tokamak divertor plasma is developed.

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Section: Introductionmentioning

confidence: 99%

Physics of ultimate detachment of a tokamak divertor plasma

Krasheninnikov¹,

2017

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“…Tokamaks with H-mode operation (Wagner et al 1982) have an important edge pedestal pressure, and hence a sharp pressure gradient in the neighbourhood of the plasma boundary. The energy content in the plasma is significantly higher than that of standard L-mode discharges.…”

Section: Introductionmentioning

confidence: 99%

A 3-D MHD equilibrium description of nonlinearly saturated ideal external kink/peeling structures in tokamaks

et al. 2015

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Novel free boundary magnetohydrodynamic equilibrium states with spontaneous three-dimensional (3-D) deformations of the plasma-vacuum interface are computed. The structures obtained look like saturated ideal external kink/peeling modes. Large edge pressure gradients yield toroidal mode number n = 1 distortions when the edge bootstrap current is large and higher n corrugations when this current is small. Linear ideal MHD stability analyses confirm the nonlinear saturated ideal kink equilibrium states produced and we can identify the Pfirsch-Schlüter current as the main linear instability driving mechanism when the edge pressure gradient is large. The dominant non-axisymmetric component of this Pfirsch-Schlüter current drives a near resonant helical parallel current density ribbon that aligns with the near vanishing magnetic shear region caused by the edge bootstrap current. This current ribbon is a manifestation of the outer mode previously found on JET (Solano 2010). We claim that the equilibrium corrugations describe structures that are commonly observed in quiescent H-mode tokamak discharges.

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“…The suppression of the locked island allows an edge transport barrier to re-form, thus re-establishing the so called high confinement mode, or H-mode [28] (Fig.4c). As a result, higher electron density n e and energy confinement time τ E are achieved when the locked mode is heating power is a marked increase in βN .…”

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Avoiding Tokamak Disruptions by Applying Static Magnetic Fields That Align Locked Modes with Stabilizing Wave-Driven Currents

et al. 2015

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Non-rotating ('locked') magnetic islands often lead to complete losses of confinement in tokamak plasmas, called major disruptions. Here locked islands were suppressed for the first time, by a combination of applied three-dimensional magnetic fields and injected millimetre waves. The applied fields were used to control the phase of locking and so align the island O-point with the region where the injected waves generated non-inductive currents. This resulted in stabilization of the locked island, disruption avoidance, recovery of high confinement and high pressure, in accordance with the expected dependencies upon wave power and relative phase between O-point and driven current.The international ITER [1] tokamak has the objective of demonstrating the scientific feasibility of magnetic confinement fusion as a source of energy. A concern towards the achievement of this goal is represented by major disruptions [1]: complete losses of confinement often initiated [2] by a non-rotating ('locked') magnetic island created by magnetic reconnection [3]. During disruptions, energy and particles accumulated in the plasma volume over several confinement times (seconds in ITER, a fraction of a second in present experiments) are lost in a few milliseconds and released on the plasma-facing materials [4]. In addition, multi-MA level currents flowing in the tokamak plasma for its sustainment and confinement are lost, also in milliseconds, thus terminating the plasma discharge and causing electromagnetic stresses that, if unmitigated, could lead to excessive device wear. Here it is shown for the first time that magnetic perturbations can be used to avoid disruptions by "guiding" the magnetic island to lock in a position where it is accessible to millimetre wave beams that fully stabilize it. Stabilization is due to locally wave-driven currents (Electron Cyclotron Current Drive, or ECCD).Magnetic control of island rotation [5] and stabilization of rotating islands by ECCD [6] were separately demonstrated in the past. Currents were either continuously driven [6] or, more efficiently, they were modulated in synch with the spontaneous island rotation [7]. Electron Cyclotron Heating (ECH) was also used for stabilization [8], but is predicted to scale unfavorably to large hot plasmas [9]. Two experiments combined magnetic perturbations -to produce the island-with ECH that stabilized it: in the first one the mode was born locked to a given phase and was stabilized by continuous ECH [10]; the second one controlled island rotation and stabilized the mode by modulated ECH [11].However, if the rotating island (typically a spontaneous, pressure-driven 'Neoclassical Tearing Mode') is not preempted or stabilized (due for example to late intervention, misalignment, or insufficient power being used for this purpose), or if the island does not ever rotate at all, it becomes necessary to suppress the locked mode. This capability was numerically modeled [12], experimentally tested [13], and is fully demonstrated here for the first time. Without this...

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Regime of Improved Confinement and High Beta in Neutral-Beam-Heated Divertor Discharges of the ASDEX Tokamak

Cited by 2,005 publications

References 0 publications

Physics of ultimate detachment of a tokamak divertor plasma

Physics of ultimate detachment of a tokamak divertor plasma

A 3-D MHD equilibrium description of nonlinearly saturated ideal external kink/peeling structures in tokamaks

Avoiding Tokamak Disruptions by Applying Static Magnetic Fields That Align Locked Modes with Stabilizing Wave-Driven Currents

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