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2008
An analytical, large aspect ratio, calculation of the drift-kinetic energy perturbation is carried out for the resistive wall mode, due to the mode resonance with the magnetic precession drifts of trapped thermal ions and electrons. Four asymptotic cases are identified and analyzed in detail. Generally, a partial stabilization of the mode is possib…
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2008
A simple formula for predicting the width of a saturated island, formed as a consequence of tearing perturbation of linear force-free fields in cylindrical geometry, is derived. The formula makes it possible to calculate the saturated island width in terms of the values of parameters characterizing the initial force-free equilibrium and can be appl…
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2008
Edge Localised Modes (ELMs) are periodic disturbances of the plasma periphery occurring in tokamaks with an H-mode edge transport barrier. As a result, a fraction of the plasma energy present in the confined hot edge plasma is transferred to the open field lines in the divertor region, ultimately appearing at the divertor target plates. These event…
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2008
We motivate the need to include collisional dissipation in gyrokinetic turbulence simulations, and constract criteria for a physically vaUd model of such dissipation. A new analytically manageable operator satisfying those criteria is presented and transformed into gyrokinetic variables. The form of conservation laws for collision operators in gyro…
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2007
In tokamak disruptions the Ohmic current is often replaced by a current of runaway electrons, which is likely to be more peaked in the center of the discharge than the predisruption current. This raises the question of the resistive stability of the postdisruption plasma, where the equilibrium current is entirely carried by the runaway electrons wh…
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2007
The linear stability of a class of force-free equilibria in cylindrical geometry is investigated. The class consists of cylindrically symmetric force-free equilibria for which the ratio between the parallel current density and the magnetic field is a step function of the radius. It is suggested that plasmas in reversed field pinches could be roughl…
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2007
A discrete spectrum of compressional Alfvén eigenmodes and ion-ion hybrid eigenmodes is found to exist above the tritium ion cyclotron frequency in the deuterium-tritium D-T plasma of a spherical tokamak power plant STPP [H. R. Wilson and et al. , 19th IAEA Fusion Energy Conference IAEA, Lyon, France, (2002), No. FT/1-4]. An equilibrium magnetic w…
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2007
Recent advances in modeling the effects of anisotropic energetic ion distributions have enabled the development of a complete coherent physics explanation of sawtooth stabilization in both conventional and spherical tokamaks. As an example, a complete model has been developed to explain the asymmetric stabilization of sawteeth with respect to neutr…
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2007
The destabilization of ideal magnetohydrodynamic ballooning modes at finite rotation shear is demonstrated for the model s - equilibrium by exploiting low magnetic shear, s , to simplify the two-dimensional stability problem to a one-dimensional eigenvalue problem. This simpler calculation captures the same features as exhibited by a full two-dimen…
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2006
Edge-localized modes (ELMs) are cyclic disturbances in the outer region of tokamak plasmas that are influential in determining present and future tokamak performance. In this Letter, we outline an approach to modeling ELMs in which we envisage toroidal peeling modes initiating a Taylor relaxation [Phys. Rev. Lett. 33 , 1139 (1974)] of a tokamak out…
Showing 71 - 80 of 118 UKAEA Paper Results