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2012
Lower hybrid current drive (LHCD) with modest powers ( 10% of the total power input) has been used for the first time to completely stabilize performance limiting neoclassical tearing modes in many COMPASS-D tokamak discharges. The stabilizing effect in these experiments is consistent with a reduction in the free energy available in the current pro…
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2012
Shallow fuelling pellets are injected from the high field side into plasmas in which ELMs have been mitigated using external magnetic perturbation coils. The data are compared with ideal assumptions in the ITER fuelling model, namely that mitigated ELMs are not affected by fuelling pellets. Firstly it is shown that during the pellet evaporation an …
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2011
Transport analysis of MAST discharges indicates that ion collisional transport is an important loss mechanism in the core of a spherical tokamak. In the strongly-varying equilibrium fields of spherical tokamaks many of the assumptions of drift kinetic and neoclassical theory (e.g. small plasma inverse aspect ratio and low ratio of toroidal Larmor r…
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2011
Axisymmetric plasma equilibria with toroidal flow are investigated using a two-fluid analysis, taking into account the presence of momentum and current drive, together with dissipative effects. The equilibria are described by a set of three equations describing the spatial variation of poloidal magnetic flux, plasma pressure and toroidal magnetic f…
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2011
Following earlier publication of a model of crack flow and filtering based on a 2-D crack representation, the model has been improved and submitted to validation by comparison with data from a number of other theoretical and experimental studies. This process has led to improved understanding of gas flow and filtering in real crack geometry and pro…
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2011
Access into H-mode is studied in the MAST tokamak when plasma is fuelled by cryogenic pellets. It is shown that pellet fuelling from the high field side allows access to Hmode in plasmas heated by neutral beams. Simple and two-stage L-H transitions are identified. The results of comparison of the L-H transitions with pellet injection with transitio…
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2010
The COMPASS tokamak, a mid-sized flexible device with ITER-like shape, which can operate in H-mode, is starting its re-established operation at the Institute of Plasma Physics in Prague. A new 600 kW, 40 keV neutral beam injection (NBI) system is foreseen as a major upgrade. Reported here are predictive simulations with the ASTRA transport code, in…
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2010
In this work, the radial transport of tracers in an H-mode run in the CUTIE code [A. Thyagaraja et al. , Phys. Plasmas 12 , 090907 (2005)] is analyzed globally. Several techniques are applied to the study of the trajectories performed by the tracers, measuring the degree of self-similarity in the motion and searching for long range spatial and temp…
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2010
It is shown that the transition from L-mode to H-mode regimes in tokamaks can be reproduced using a two-fluid, fully electromagnetic, plasma model when a suitable particle sink is added at the edge. Such a model is implemented in the CUTIE code [A. Thyagaraja et al. , Eur. J. Mech. B/Fluids 23 , 475 (2004)] and is illustrated on plasma parameters t…
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2010
Inviscid, incompressible hydrodynamics and incompressible ideal magnetohydrodynamics MHD share many properties such as time-reversal invariance of equations, conservation laws, and certain topological features. In three dimensions, these systems may lead to singular solutions involving vortex and current sheets. While dissipative viscoresistive eff…
Showing 21 - 30 of 66 UKAEA Paper Results