76 research outputs found
ELM control by resonant magnetic perturbations on JET and MAST
In both JET and MAST, the Error Field Correction Coils (EFCCs) have been
used recently in order to attempt to control Type I Edge Localised Modes
(ELMs), which represent a major threat to the lifetime of plasma facing
components in ITER. Using vacuum magnetic modelling it is suggested that
the ELM mitigation observed at JET could be related to the
stochastization of the magnetic field at the edge. Indeed, the onset of
ELM mitigation is found to be correlated with a certain level of the
Chirikov parameter profile. Initial MAST results are presented which
show an effect of EFCCs on the ELMs, again compatible with edge
stochastization according to the modelling. New coils dedicated to ELM
control are ready for use on MAST this year and are presented here
briefly
OVERVIEW OF CORE DIAGNOSTICS FOR TEXTOR
The diagnostic system of TEXTOR comprises about 50 individual diagnostic devices. Since the start of the Trilateral Euregio Cluster collaboration, part of the emphasis in the experimental program has shifted toward the study of physics processes in the plasma core. To aid these studies several new and advanced core diagnostics have been implemented, whereas a number of other core diagnostics have been upgraded to higher resolution, more channels, and better accuracy. In this paper a brief overview is given of the present set of plasma core diagnostics at TEXTOR.X1114sciescopu
Chapter 3: MHD stability, operational limits and disruptions
Progress in the area of MHD stability and disruptions, since the
publication of the 1999 ITER Physics Basis document (1999 Nucl.
Fusion 39 2137-2664), is reviewed. Recent theoretical and
experimental research has made important advances in both understanding
and control of MHD stability in tokamak plasmas. Sawteeth are
anticipated in the ITER baseline ELMy H-mode scenario, but the tools
exist to avoid or control them through localized current drive or fast
ion generation. Active control of other MHD instabilities will most
likely be also required in ITER. Extrapolation from existing experiments
indicates that stabilization of neoclassical tearing modes by highly
localized feedback-controlled current drive should be possible in ITER.
Resistive wall modes are a key issue for advanced scenarios, but again,
existing experiments indicate that these modes can be stabilized by a
combination of plasma rotation and direct feedback control with
non-axisymmetric coils. Reduction of error fields is a requirement for
avoiding non-rotating magnetic island formation and for maintaining
plasma rotation to help stabilize resistive wall modes. Recent
experiments have shown the feasibility of reducing error fields to an
acceptable level by means of non-axisymmetric coils, possibly controlled
by feedback. The MHD stability limits associated with advanced scenarios
are becoming well understood theoretically, and can be extended by
tailoring of the pressure and current density profiles as well as by
other techniques mentioned here. There have been significant advances
also in the control of disruptions, most notably by injection of massive
quantities of gas, leading to reduced halo current fractions and a
larger fraction of the total thermal and magnetic energy dissipated by
radiation. These advances in disruption control are supported by the
development of means to predict impending disruption, most notably using
neural networks. In addition to these advances in means to control or
ameliorate the consequences of MHD instabilities, there has been
significant progress in improving physics understanding and modelling.
This progress has been in areas including the mechanisms governing NTM
growth and seeding, in understanding the damping controlling RWM
stability and in modelling RWM feedback schemes. For disruptions there
has been continued progress on the instability mechanisms that underlie
various classes of disruption, on the detailed modelling of halo
currents and forces and in refining predictions of quench rates and
disruption power loads. Overall the studies reviewed in this chapter
demonstrate that MHD instabilities can be controlled, avoided or
ameliorated to the extent that they should not compromise ITER
operation, though they will necessarily impose a range of constraints
Toroidal plasma rotation induced by the Dynamic Ergodic Divertor in the TEXTOR tokamak
The first results of the Dynamic Ergodic Divertor in TEXTOR, when operating in the m/n=3/1 mode configuration, are presented. The deeply penetrating external magnetic field perturbation of this configuration increases the toroidal plasma rotation. Staying below the excitation threshold for the m/n=2/1 tearing mode, this toroidal rotation is always in the direction of the plasma current, even if the toroidal projection of the rotating magnetic field perturbation is in the opposite direction. The observed toroidal rotation direction is consistent with a radial electric field, generated by an enhanced electron transport in the ergodic layers near the resonances of the perturbation. This is an effect different from theoretical predictions, which assume a direct coupling between rotating perturbation and plasma to be the dominant effect of momentum transfer
Organizational architecture, ethical culture, and perceived unethical behavior towards customers:Evidence from wholesale banking
In this study, we propose and test a model of the effects of organizational ethical culture and organizational architecture on the perceived unethical behavior of employees towards customers. This study also examines the relationship between organizational ethical culture and moral acceptability judgment, hypothesizing that moral acceptability judgment is an important stage in the ethical decision-making process. Based on a field study in one of the largest financial institutions in Europe, we found that organizational ethical culture was significantly related to the perceived frequency of unethical behavior towards customers and to the moral acceptability judgment of this type of unethical behavior. No support was found for the claim that features of organizational architecture are associated with the perceived frequency of unethical behavior towards customers. This is the first study to document the differential effects of organizational architecture and organizational ethical culture on perceived unethical behavior of employees towards customers, in wholesale banking. Implications for managers and future research are discussed
Plasma-wall interaction studies within the EUROfusion consortium:progress on plasma-facing components development and qualification
\u3cp\u3eThe provision of a particle and power exhaust solution which is compatible with first-wall components and edge-plasma conditions is a key area of present-day fusion research and mandatory for a successful operation of ITER and DEMO. The work package plasma-facing components (WP PFC) within the European fusion programme complements with laboratory experiments, i.e. in linear plasma devices, electron and ion beam loading facilities, the studies performed in toroidally confined magnetic devices, such as JET, ASDEX Upgrade, WEST etc. The connection of both groups is done via common physics and engineering studies, including the qualification and specification of plasma-facing components, and by modelling codes that simulate edge-plasma conditions and the plasma-material interaction as well as the study of fundamental processes. WP PFC addresses these critical points in order to ensure reliable and efficient use of conventional, solid PFCs in ITER (Be and W) and DEMO (W and steel) with respect to heat-load capabilities (transient and steady-state heat and particle loads), lifetime estimates (erosion, material mixing and surface morphology), and safety aspects (fuel retention, fuel removal, material migration and dust formation) particularly for quasi-steady-state conditions. Alternative scenarios and concepts (liquid Sn or Li as PFCs) for DEMO are developed and tested in the event that the conventional solution turns out to not be functional. Here, we present an overview of the activities with an emphasis on a few key results: (i) the observed synergistic effects in particle and heat loading of ITER-grade W with the available set of exposition devices on material properties such as roughness, ductility and microstructure; (ii) the progress in understanding of fuel retention, diffusion and outgassing in different W-based materials, including the impact of damage and impurities like N; and (iii), the preferential sputtering of Fe in EUROFER steel providing an in situ W surface and a potential first-wall solution for DEMO.\u3c/p\u3
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