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2010
MAST plasmas with a safety factor above unity and a profile with either weakly reversed shear, or broad low shear regions, regularly exhibit long-lived saturated ideal magnetohydrodynamic (MHD) instabilities. The toroidal rotation is flattened in the presence of such perturbations and the fast ion losses are enhanced. These ideal modes, distinguish…
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2010
The impact of resonance magnetic perturbations (RMP) on the structure of the edge transport barrier has been studied. A new model for the density pump-out mechanism during the stochastization of the plasma edge is proposed. The observed phenomena are explained as a result of the impact of the ambipolar electric field, which is modified during RMP, …
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2010
Several diagnostic systems in magnetically confined fusion plasmas provide line-integrated measurements along chords, including bolometry, visible light, soft-Xray ~SXR!, or neutron diagnostics. The task of retrieval of spatial distribution of the plasma emissivity from the line-integrated measurements constitutes an important part of fusion data a…
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2009
In recent JET experiments, Lower Hybrid (LH) power losses in the Scrape-Off Layer (SOL) were characterized using infra-red (IR) thermography. Hot spots were observed on objects intercepting the field lines passing in front of the LH launcher, i.e. on poloidal limiters and on dumplates located at the top of the tokamak; their locations being in good…
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2009
In this paper, significant results in the heating and current drive domains obtained at JET in the past few years following systems upgrade and dedicated experimental time, will be reviewed. Firstly, an overview of the new Ion Cyclotron Resonance Frequency (ICRF) heating capabilities will be presented i.e. results trom the ITER-Like ICRF antenna (I…
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2009
A Sub-Harmonic Arc Detection (SHAD) system has been installed on the transmission lines feeding the JET ICRF ITER-like-Antenna (ILA). Along with the commissioning of SHAD, extensive measurements of the RF field in the transmission lines were carried-out using fast sampling (125 Mb/s) oscilloscopes. The system is described, and the SHAD ability to d…
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2009
ITER and future superconducting fusion machines need efficient wall conditioning techniques for routine operation in between shots in the presence oi permanent high magnetic field for wall cleaning, surface isotope exchange and to control the in-vessel long term tritium retention. Ion Cyclotron Wall Conditioning (ICWC) based on the ICRF discharge i…
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2009
Over the past two decades, the increase in neutral-beam heating and particle production in magnetically confined fusion plasmas has led to an increase in energetic particle driven mode activity, much of which has an electromagnetic signature which can be detected by the use of external Mirnov coils. Typically, the frequency and spatial wave number …
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2009
Beam emission spectroscopy BES of the energetic deuterium D 0 heating beams can provide a means of characterizing the density turbulence in tokamak plasmas. First such measurements have been performed on the MAST spherical tokamak using a trial BES system, which shares the collection optics of the charge-exchange recombination spectroscopy system. …
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2009
The sawtooth control mechanism in plasmas employing off-axis toroidally propagating ion cyclotron resonance waves in tokamaks is reinvestigated. The radial drift excursion of energetic passing ions distributed asymmetrically in the velocity parallel to the magnetic field determines stability when the rational q 1/4 1 surface resides within a narrow…
Showing 351 - 360 of 500 UKAEA Paper Results