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2012
Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak have sufficient resolution to capture plasma evolution during the short period between edge-localized modes (ELMs). Immediately after the ELM, steep gradients in pressure, P , and density, n e , form pedestals close to the separatrix, and they then expand into the core. Local gyrok…
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2011
Nonlinear gyrokinetic simulations are conducted to investigate turbulent transport in tokamak plasmas with rotational shear. At sufficiently large flow shears, linear instabilities are suppressed, but transiently growing modes drive subcritical turbulence whose amplitude increases with flow shear. This leads to a local minimum in the heat flux, ind…
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2011
Pedestal profiles that span the ELM cycle have been obtained and used to test the idea that the pedestal pressure gradient in MAST is limited by the onset of Kinetic Ballooning Modes (KBMs). During the inter-ELM period of a regularly type I ELM-ing discharge on MAST, the pressure pedestal height and width increase together while the pressure gradie…
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2011
First-principles numerical simulations are used to describe a transport bifurcation in a differentially rotating tokamak plasma. Such a bifurcation is more probable in a region of zero magnetic shear than one of finite magnetic shear, because in the former case the component of the sheared toroidal flow that is perpendicular to the magnetic field h…
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2010
The effect of flow shear on turbulent transport in tokamaks is studied numerically in the experimentally relevant limit of zero magnetic shear. It is found that the plasma is linearly stable for all nonzero flow shear values, but that subcritical turbulence can be sustained nonlinearly at a wide range of temperature gradients. Flow shear increases …
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2008
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2007
Principal techniques and trends in the validation and analysis of data in magnetic fusion research are described and examples of applications are given. Wellestablished methods to obtain key physical quantities are outlined, as well as newer techniques employing integrated analysis of multiple diagnostics to improve quality and extract additional i…
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2004
Gyrokinetic microstability analyses, with and without electromagnetic effects, are presented for a spherical tokamak plasma equilibrium closely resembling that from a high confinement mode ( H mode ) discharge in the mega-ampere spherical tokamak ( MAST ) [ A. Sykes et al. , Nucl. Fusion 41 , 1423 ( 2001 )] . Electrostatic ion temperature gradient …
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2003
The generation of zonal flows and their interplay with drift wave turbulence is studied numerically using a model based on the Hasegawa–Mima equation, with an electron response depending only on the fluctuating part of the electrostatic potential. In regimes dominated by the diamagnetic velocity, large-amplitude nonlinear oscillations are observe…
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2000
H -mode operation has been achieved in high current I p . 200 kA plasmas in the START spherical tokamak for both neutral-beam-injection-heated and Ohmic discharges. The transition to H mode features the development of well-defined edge pedestals in density and temperature, which signifies the formation of an edge-transport barrier, and associated e…
Showing 41 - 50 of 51 UKAEA Paper Results