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2012
In this paper, current profiles for plasma discharges on the mega-ampere spherical tokamak are directly calculated from pickup coil, flux loop, and motional-Stark effect observations via methods based in the statistical theory of Bayesian analysis. By representing toroidal plasma current as a series of axisymmetric current beams with rectangular cr…
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2012
A new model of the L–H transition in tokamaks is proposed, based on the criterion that the transition occurs when plasma turbulence and shear Alfvén waves compete in the vicinity of the last-closed flux surface. The model is used to predict the scaling of the H-mode access power, PL–H, with magnetic and plasma variables. The predictio…
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2012
We develop an atomistic spin-lattice-dynamics model for simulating energy relaxation in magnetic materials. The model explicitly solves equations of motion for the atoms and spins, and includes interaction with electron excitations. We apply the model to simulate the dynamics of propagation of a compressive elastic wave in iron. We find that coupli…
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2012
Frank-Read sources are among the most important examples of dislocation sources in crystals, and their operation facilitates dislocation multiplication and hence yield and plastic flow. Iron is known to become highly elastically-anisotropic as the alpha - gamma transition at 912 degrees centigrage is approached, a temperature regime of critical imp…
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2012
The distortion of the plasma boundary when three-dimensional resonant magnetic perturbations are applied has been measured in MAST H-mode plasmas. When the n = 3 resonant magnetic perturbations are applied to control edge localised modes, the plasma experiences a strong toroidal corrugation. The displacement of the plasma boundary is measured at va…
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2012
The VUV/XUV spectral region is particularly rich in lines emitted by plasmas with temperatures = 30 keV used in fusion research. Examples are presented of analyses of JET tokamak data involving C VUV/XUV radiation. In the first, the C IV divertor emission is modelled, with agreement between theory and experiment to within the measurement accuracy o…
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2012
The application of resonant magnetic perturbations with toroidal mode number n = 4 or n = 6 is observed to result in a significant increase in ELM frequency, despite a reduction in the edge pressure gradient. A picture for how type-I ELMs are mitigated, or destabilised, when magnetic perturbations are applied is proposed. Despite the magnetic pertu…
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2012
In fusion negative ion sources, the negative ions are formed on the caesiated plasma grid predominantly by hydrogen atoms from the plasma. The space charge of the negative ions leaving the wall is not fully compensated by incoming positive ions and at high enough emission a virtual cathode is formed. This virtual cathode limits the flux of negative…
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2012
The paper is a tribute to Nicol Peacock and has a focus on interests and developments at Culham Laboratory from ~ 1970 when Nicol led the UKAEA spectroscopy team. The paper charts a little of the evolution of these models and their data through the seventies and eighties on into this century at Culham. The paper concludes with the state of efforts …
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2012
Sawtooth control using electron cyclotron current drive (ECCD) has been demonstrated in ITER-like plasmas with a large fast ion fraction, wide q = 1 radius and long uncontrolled sawtooth period in DIII-D. The sawtooth period is minimized when the ECCD resonance is just inside the q = 1 surface. Sawtooth destabilization using driven current inside q…
Showing 1821 - 1830 of 2526 UKAEA Paper Results