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Abingdon, United Kingdom

The European Atomic Energy Community is an international organisation founded in 1957 with the purpose of creating a specialist market for nuclear power in Europe, developing nuclear energy and distributing it to its member states while selling the surplus to non-member states. It is legally distinct from the European Union , but has the same membership, and is governed by the EU's institutions.Currently, its main focus is on the construction of the International Fusion Reactor ITER financed under the nuclear part of FP7. Euratom also provides a mechanism for providing loans to finance nuclear projects in the EU.It was established by the Euratom Treaty on 25 March 1957 alongside the European Economic Community/EEC, being taken over by the executive institutions of the EEC in 1967. Although other communities were merged in 1993 and 2009, the nuclear program has maintained a legally distinct nature from the European Union. Wikipedia.

Installation of the ITER-like Wall (ILW) in JET, has allowed a direct comparison of operation with all carbon plasma facing components (PFCs) to an all metal beryllium/tungsten first-wall under otherwise nearly identical conditions. The JET results are compared with experience from ASDEX-Upgrade where there was a gradual change to a full tungsten first-wall over an extended period. The scope of this review ranges from experience with machine conditioning, impurities and breakdown to material migration, fuel retention, disruptions, impact on operational space, energy confinement and compatibility with impurity seeding. Significant changes are reported, not only in the physics directly related to plasma-surface interactions but also to the main plasma which is strongly affected in unexpected ways, impacting many aspects of tokamak operation. © 2013 Euratom. Published by Elsevier B.V. All rights reserved. Source

The effects of the fusion born β particles on the stability of the RWM are numerically investigated for one of the advanced steady state scenarios in ITER. The β contribution is found to be generally stabilizing, compared with the thermal particle kinetic contribution alone. The same conclusion is achieved following both a perturbative and selfconsistent approach. The latter generally predicts less stabilization than the former. At high enough plasma pressure, the self-consistent approach predicts two unstable branches for the ITER plasma studied here. The stabilizing effect from β particles is found to be generally weak, in particular in terms of the modification of the stability boundary. The effect is more pronounced only at fast enough plasma rotation frequency, roughly matching the β precession frequency, which is in the order of a few per cent of the toroidal Alfvén frequency for ITER. A simple, energy principle based, fishbone-like dispersion relation is proposed to gain a qualitative understanding of the numerical results. © 2010 IAEA, Vienna. Source

Webster A.J.,EURATOM
Nuclear Fusion | Year: 2012

The edge of a tokamak plasma is interesting due to its geometrical structure that is difficult to model mathematically and computationally, its tendency to form transport barriers with increased confinement of energy and momentum, and the edge-localized instabilities associated with transport barriers that threaten the lifetime of components in large tokamaks. Ideal magnetohydrodynamics (MHD) is generally well understood, but only in the past decade has a good theoretical understanding emerged of MHD stability near the plasmas' separatrix when one or more X-points are present. By reviewing and discussing our theoretical understanding of ideal MHD stability of the plasma's edge, a clear picture emerges for its ideal stability. Conclusions are: ideal MHD will limit the width of strong transport barriers at the plasma's edge, a strong edge transport barrier will be associated with ELMs, ELMs will have a maximum toroidal mode number, will be preceded by smaller precursor instabilities, and can be triggered by sufficient changes to either the edge or the core plasma. Observations are made for the mechanisms responsible for edge transport barriers and ELMs, some leading to experimental predictions, others highlighting important open questions. © 2012 IAEA, Vienna. Source

Chapman I.T.,EURATOM
Plasma Physics and Controlled Fusion | Year: 2011

The sawtooth instability in tokamak plasmas results in a periodic reorganization of the core plasma. A typical sawtooth cycle consists of a quiescent period, during which the plasma density and temperature increase, followed by the growth of a helical magnetic perturbation, which in turn is followed by a rapid collapse of the central pressure. The stabilizing effects of fusion-born a particles are likely to lead to long sawtooth periods in burning plasmas. However, sawteeth with long quiescent periods have been observed to result in the early triggering of neo-classical tearing modes (NTMs) at low plasma pressure, which can, in turn, significantly degrade confinement. Consequently, recent experiments have identified various methods to deliberately control sawtooth oscillations in an attempt to avoid seeding NTMs whilst retaining the benefits of small, frequent sawteeth, such as the prevention of core impurity accumulation. Sawtooth control actuators include current drive schemes, such as electron cyclotron current drive, and tailoring the fast ion population in the plasma using neutral beam injection or ion cyclotron resonance heating. © 2011 IOP Publishing Ltd. Source

Igochine V.,EURATOM
Nuclear Fusion | Year: 2012

The advanced tokamak regime is a promising candidate for steady-state tokamak operation which is desirable for a fusion reactor. This regime is characterized by a high bootstrap current fraction and a flat or reversed safety factor profile, which leads to operation close to the pressure limit. At this limit, an external kink mode becomes unstable. This external kink is converted into the slowly growing resistive wall mode (RWM) by the presence of a conducting wall. Reduction of the growth rate allows one to act on the mode and to stabilize it. There are two main factors which determine the stability of the RWM. The first factor comes from external magnetic perturbations (error fields, resistive wall, feedback coils, etc). This part of RWM physics is the same for tokamaks and reversed field pinch configurations. The physics of this interaction is relatively well understood and based on classical electrodynamics. The second ingredient of RWM physics is the interaction of the mode with plasma flow and fast particles. These interactions are particularly important for tokamaks, which have higher plasma flow and stronger trapped particle effects. The influence of the fast particles will also be increasingly more important in ITER and DEMO which will have a large fraction of fusion born alpha particles. These interactions have kinetic origins which make the computations challenging since not only particles influence the mode, but also the mode acts on the particles. Correct prediction of the plasma-RWM interaction is an important ingredient which has to be combined with external field's influence (resistive wall, error fields and feedback) to make reliable predictions for RWM behaviour in tokamaks. All these issues are reviewed in this paper. © 2012 IAEA, Vienna. Source

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