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2003
Particle transport in magnetized plasmas is investigated with a fluid model of drift wave turbulence. An analytical calculation shows that magnetic field curvature and thermodiffusion drive an anomalous pinch. The curvature driven pinch velocity is consistent with the prediction of turbulence equipartition theory. The thermodiffusion flux is found …
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2003
A model for the solar coronal magnetic field is proposed where multiple directed loops evolve in space and time. Loops injected at small scales are anchored by footpoints of opposite polarity moving randomly on a surface. Nearby footpoints of the same polarity aggregate, and loops can reconnect when they collide. This may trigger a cascade of furth…
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2003
In view of the modification to the Joint European Torus (JET) plasma facing components foreseen for the 2004 shutdown, the disruption design criteria for invessel components have been updated building on the operational experience with divertor plasmas gained since the early 1990s. In fast disruptions the largest contribution to the electromechanic…
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2003
Combined operation of Lower Hybrid (LH) and Ion Cyclotron Resonance Frequency (ICRF) waves can result in a degradation of the LH wave coupling, as observed both in the Tore Supra and JET tokamaks. The reflection coefficient on the part of the LH launcher magnetically connected to the powered ICRF antenna increases, suggesting a local decrease in th…
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2002
Electron-Bernstein waves (EBW) were excited in the plasma by mode converted extraordinary ( X ) waves launched from the high field side of the COMPASS-D tokamak at different toroidal angles. It has been found experimentally that X -mode injection perpendicular to the magnetic field provides maximum heating efficiency. Noninductive currents of up to…
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2002
Spontaneous acceleration of ions to suprathermal energies is observed during magnetic reconnection in the Mega-Ampere Spherical Tokamak (MAST). A high-energy tail is observed in the iondistribution function following each internal reconnection event in Ohmic discharges. This phenomenon is explained in terms of runaway ion acceleration in the electr…
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2002
Neutral atoms in the tokamak edge affect the electric field and plasma flow through charge exchange. Here, it is shown that these effects depend sensitively on the poloidal location of the atoms. It is found that the radial electric field and toroidal flow velocity in a collisional edge plasma are largest if the atoms are concentrated on the inboar…
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2002
H -mode plasmas have been achieved on the MAST spherical tokamak at input power considerably higher than predicted by conventional threshold scalings. Following L - H transition, a clear improvement in energy confinement is obtained, exceeding recent international scalings even at densities approaching the Greenwald density limit. Transition is acc…
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2002
The transport of test particle ensembles moving in turbulent electrostatic fields governed by the Hasegawa–Mima equation is investigated. It ranges from subdiffusive to ballistic, depending on the size (in terms of thermal ion Larmor radii) of the domain considered, and on the magnitude of the background density gradient. In addition to the elect…
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2002
Spontaneous transitions from the low ‘‘L-mode’’ to high ‘‘H-mode’’ of tokamak plasma confinement, first observed during neutral beam heating experiments on ASDEX, are now routinely achieved in many tokamak experiments. The H-mode regime is attractive as it offers the possibility of enhanced confinement, and thus a route towards a mo…
Showing 441 - 450 of 507 UKAEA Paper Results