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2014
On MAST, compressional Alfven eigenmodes can be destabilized by the presence of a sufficiently large population of energetic particles in the plasma. This dependence was studied in a series of very similar discharges in which increasing amounts of hydrogen were puffed into a deuterium plasma. A simple method to estimate the isotopic ratio nH/nD usi…
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2014
Compressional Alfven and ion-ion hybrid waves excited by energetic beam ions are studied in plasmas with two ion species. In our experiment, a hydrogendeuterium (H-D) plasma is used to produce instabilities similar to those likely to be present in the burning deuterium-tritium plasmas of future tokamaks. Modes are suppressed in the deuterium cyclot…
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2014
After the first high power D-T experiment in JET in 1997 (DTE1), when JET was equipped with Carbon PFC’s, a proposed second high power (up to ~40MW) D-T campaign (DTE2) in the current Be/W vessel will address essential operational, technical, diagnostics and scientific issues in support of ITER. These experiments are proposed to minimize the risk…
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2013
Remarkable progress has been made in diagnosing energetic particle instabilities on present-day machines and in establishing a theoretical framework for describing them. This overview describes the much improved diagnostics of Alfven instabilities and modelling tools developed world-wide, and discusses progress in interpreting the observed phenomen…
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2012
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2012
A general introduction is given to ideal magnetohydrodynamic (MHD) waves, using linear perturbations of ideal MHD equations. Subsequently the shear Alfvén waves are shown to form a discrete spectrum of Global Alfvén Eigenmodes in current-carrying cylindrical plasmas and Toroidal Alfvén Eigenmodes in toroidal plasmas. A comparison between theory …
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2011
Neutral beam injection into reversed magnetic shear DIII-D and ASDEX Upgrade plasmas produces a variety of Alfvénic activity including toroidicity-induced Alfvén eigenmodes and reversed shear Alfvén eigenmodes (RSAEs). These modes are studied during the discharge current ramp phase when incomplete current penetration results in a high central sa…
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2011
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2010
Instabilities of Alfvén Eigenmodes (AEs) are often excited by a super-Alfvénic population of fast ions accelerated with ion cyclotron resonance heating (ICRH) or produced by neutral beam injection (NBI) in present-day tokamaks. In view of the next-step burning plasma experiments with super-Alfvénic alpha-particles, the experimental data on AE in…
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2010
A fully nonlinear model is developed for the bump-on-tail instability including the effects of dynamical friction drag and velocity space diffusion on the energetic particles driving the wave. The results show that drag provides a destabilizing effect on the nonlinear evolution of waves. Specifically, in the early nonlinear phase of the instability…
Showing 51 - 60 of 81 UKAEA Paper Results