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Sharapov S.E.,EURATOM | Alper B.,EURATOM | Berk H.L.,University of Texas at Austin | Borba D.N.,EURATOM | And 39 more authors.
Nuclear Fusion | Year: 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 Alfvén instabilities and modelling tools developed world-wide, and discusses progress in interpreting the observed phenomena. A multi-machine comparison is presented giving information on the performance of both diagnostics and modelling tools for different plasma conditions outlining expectations for ITER based on our present knowledge. © 2013 IAEA, Vienna.

Perez Von Thun C.,Culham Science Center | Perez Von Thun C.,Max Planck Institute for Plasma Physics (Garching) | Perez Von Thun C.,JET EFDA Close Support Unit | Salmi A.,Culham Science Center | And 19 more authors.
Nuclear Fusion | Year: 2012

The impact of fishbone oscillations onto a confined fast-ion population is simulated for a JET plasma and benchmarked against experiment quantitatively with the help of neutron rate measurements. The transient drops in volume integrated neutron emission are found to be mainly caused by the spatial redistribution of the (neutral beam injected) fast-ion population confined in the plasma rather than by fast-ion loss. The simulations yield a quadratic dependence of the neutron drop on the fishbone amplitude. It is found that the simulations are able to correctly reproduce the magnitude of the experimentally observed drop in volume integrated neutron emission to within a factor 2. Furthermore, frequency chirping is found to be important. Omitting the fishbone frequency chirp in the simulations reduces the magnitude of the neutron rate drop (and hence fast-ion redistribution) to about half its original value. © 2012 IAEA, Vienna.

Barbier D.,JET EFDA Close Support Unit | Barbier D.,CEA Cadarache Center | Batistoni P.,ENEA | Coad P.,EURATOM | Likonen J.,Tekes
Fusion Engineering and Design | Year: 2011

The JET Task Force Fusion Technology (TF-FT) was launched in 2000 to use the unique capabilities, facilities and operating experience at JET to provide significant contributions to the research programme on both JET and ITER. This paper presents the most recent results obtained within the JET TF-FT programme. The Tritium (T) retention measurements have confirmed high surface but little bulk T concentrations on the MKII-SRP divertor tiles and T thermal desorption tests confirmed the necessity to reach at least 600 °C. From the 2007 shutdown the MKII-HD (more ITER like) divertor has revealed some slight changes in the nature of the erosion/deposition. In order to improve analysis, time resolution devices such as quartz micro-balances and rotating collectors have been located beneath the divertor for deposition and plasma physics correlations. Due to improvement of dedicated models and technologies, in situ laser techniques for detritiation and characterisation/removal have provided encouraging results on quantitative characteristics (composition, thickness, adherence, temperature) of deposited films on plasma facing components. A particular effort on temperature control of the new metallic ITER-like wall (ILW) that is presently being installed in JET has been pursued with active laser infrared thermography. JET TF-FT also contributes to the operator strategy to comply with the safety agency requirements for T management. Recent results on two major topics purification of tritiated water and development of the 3He method for the determination of the T concentration in waste drums are presented. Finally, this paper also presents some activities in preparation of the ILW for the pre-characterisation of marker tiles and the refurbishment of diagnostics for deposition characterisation. © 2011 Elsevier B.V. All rights reserved.

Testa D.,Culham Center for Fusion Energy | Testa D.,Ecole Polytechnique Federale de Lausanne | Carfantan H.,Culham Center for Fusion Energy | Carfantan H.,French National Center for Scientific Research | And 7 more authors.
Europhysics Letters | Year: 2010

In this work we report the successful application of an innovative method, based on the Sparse Representation of signals, to perform a real-time, unsupervised detection of the individual components in a frequency degenerate, multi-harmonic spectrum, using a small number of data unevenly sampled in the spatial domain. This method has been developed from its original applications in astronomy, and is now routinely used in the JET thermonuclear fusion experiment to obtain the decomposition of a spectrum of high-frequency (∼10-500 kHz range) magnetic instabilities with a sub-ms time resolution, allowing the real-time tracking of its individual components as the plasma background evolves. This work opens a path towards developing realtime control tools for electro-magnetic instabilities in future fusion devices aimed at achieving a net energy gain. More generally, the speed and accuracy of this algorithm is recommended for instances of physics measurements and control engineering where an unsupervised, real-time decomposition of a degenerate signal is required from a small number of data. Copyright © EPLA, 2010.

Versloot T.W.,EURATOM | Sartori R.,Fusion for Energy F4E | Rimini F.,JET EFDA Close Support Unit | De Vries P.C.,EURATOM | And 20 more authors.
Nuclear Fusion | Year: 2011

The experiment described in this paper is aimed at characterization of ELMy H-mode discharges with varying momentum input, rotation, power deposition profiles and ion to electron heating ratio obtained by varying the proportion between ion cyclotron (IC) and neutral beam (NB) heating. The motivation for the experiment was to verify if the basic confinement and transport properties of the baseline ITER H-mode are robust to these changes, and similar to those derived mostly from dominant NB heated H-modes. No significant difference in the density and temperature profiles or in the global confinement were found. Although ion temperature profiles were seen to be globally stiff, some variation of stiffness was obtained in the experiment by varying the deposition profiles, but not one that could significantly affect the profiles in terms of global confinement. This analysis shows the thermal plasma energy confinement enhancement factor to be independent of the heating mix, for the range of conditions explored. Moreover, the response of the global confinement to changes in density and power were also independent of heating mix, reflecting the changes in the pedestal, which is in agreement with globally stiff profiles. Consistently, the pedestal characteristics (pressure and width) and their dependences on global parameters such as density and power were the same during NB only or with predominant IC heating. © 2011 IAEA, Vienna.

Testa D.,Ecole Polytechnique Federale de Lausanne | Carfantan H.,University Of Toulouse Cnrs | Fasoli A.,Ecole Polytechnique Federale de Lausanne | Goodyear A.,Culham Center for Fusion Energy | And 6 more authors.
Fusion Engineering and Design | Year: 2011

We present the real-time VME system used to detect and track MHD instabilities, and particularly Alfvén Eigenmodes, on the JET tokamak [J. Wesson, Tokamaks, 3rd ed., Oxford Science Publication, Oxford, 2003, p. 617]. This system runs on a 1 kHz clock cycle, and allows performing a real-time, unsupervised and blind detection, decomposition and tracking of the individual components in a frequency-degenerate, multi-harmonic spectrum, using a small number of input data which are unevenly sampled in the spatial domain. This makes it possible to follow in real-time the detected modes as the plasma background evolves, and measure in real-time their frequency, damping rate, toroidal mode-number and relative amplitude. The successful implementation of this system opens a clear path towards developing real-time control tools for electro-magnetic instabilities in future fusion devices aimed at achieving a net energy gain, such as ITER [J. Wesson, Tokamaks, 3rd ed., Oxford Science Publication, Oxford, 2003, p. 711]. © 2011 Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fdrale de Lausanne.

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