UKAEA Journals

Showing 1 - 10 of 49 Journals Results

The impact of plasma shaping through magnetic well modifications on the stability of resistive ballooning modes in tokamaks is analysed, also including finite diamagnetic flows. Various limiting cases of the dispersion relation, obtained by matching the averaged ballooning equation across the ideal and resistive layers, are analysed. It is found th…

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The published version of this paper is currently under embargo and will be available on 02/08/2022

Kinetic treatments of drift tearing modes that match an inner, resonant layer solution to an external MHD solution, can fail to match the ideal MHD boundary condition on the parallel electric field. In this paper we demonstrate how consideration of ion sound and ion Landau damping effects achieves this, placing the theory on a firm footing. The …

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A new drift-kinetic theory of the ion response to magnetic islands in tokamak plasmas is presented. Small islands are considered, with widths w much smaller than the plasma radius r, but comparable to the trapped ion orbit width ρ_bi. An expansion in w/r reduces the system dimensions from five down to four. In the absence of an electrostatic poten…

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Starting from expressions in Connor et al. (1988), we derive a one-dimensional tearing equation similar to the approximate equation obtained by Hegna & Callen (1994); Nishimura et al. (1998), but for more realistic toroidal equilibria. The intention is to use this approximation to explore the role of steep H-mode pedestals, bootstrap currents a…

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A set of layer equations for determining the stability of semi-collisional tearing modes in an axisymmetric torus, incorporating neoclassical physics, in the small ion Larmor radius limit is provided. These can be used as an inner layer module for inclusion in numerical codes that asymptotically match the layer to toroidal calculations of the teari…

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An explanation of the observed improvement in H-mode pedestal characteristics with increasing core plasma pressure or poloidal beta, pol b , as observed in MAST and JET, is sought in terms of the impact of the Shafranov shift, D¢ , on ideal ballooning MHD stability. To illustrate this succinctly, a self-consistent treatment of the low magnetic she…

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The role of anisotropic thermal diffusivity on tearing mode stability is analysed in general toroidal geometry following similar techniques to Glasser et al [A H Glasser, et al, Phys. Fluids 18 (1975) 875], although a stronger ordering of the plasma compressibility is required. Resistive layer equations are obtained for a resistive MHD model with a…

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We investigate the linear theory of the ion-temperature-gradient (ITG) mode, with the goal of developing a general understanding that may be applied to stellarators. We highlight the Wendelstein 7X (W7-X) device. Simple fluid and kinetic models that follow closely from existing literature are reviewed and two new first-principle models are presente…