1,721,005 research outputs found
A discrete geometric formulation for eddy-current problems in fusion devices
No full textAll thermonuclear controlled fusion devices under construction or design have such high performances to require a special care in the dimensioning of various components, specically from the electromagnetic point of view. To this purpose, it is fundamental to develop models which are both accurate (i.e. able to describe the physical phenomena) and predictive (i.e. useful not only to explain what happens in running experiments, but also to reliably extrapolate to
other range of parameters).
The dynamics of fusion plasmas is often conveniently described by Magneto-Hydro-Dynamics (MHD) equations, which predict that some unstable evolution modes may exist. On the other hand, the complexity of the intrinsically 3D model of the interactions between a realistic unstable plasma, the surrounding passive structures (important to guarantee a good MHD stability) and the active conductors (coils) require the numerical solution of challenging electromagnetic problems.
In this work a discrete geometric formulation for eddy-current problems in the frequency domain is developed; the magnetic elds produced by a typical active coil system is calculated in the presence of 3D conductive structures
A novel approach for solving three dimensional eddy current problems in fusion devices
No full textWe present a technique to efficiently solve 3D eddy current problems in fusion devices, whose structuresexhibit a geometrical symmetry. The proposed approach is based on the exploitation of symmetry viaharmonic analysis and it is suitable to treat also problems where the field sources (plasma or externalcoils) do not share the domain symmetry. A simple test case is presented to describe the methodology.Then, a more complicated geometry is considered, which represents a realistic vacuum vessel of an ITERlike fusion device (double layer structure with several portholes). The results are discussed for bothaxisymmetric and non-axisymmetric excitations in frequency domain
Calculation of 3-D Magnetic Fields Produced by MHD Active Control Systems in Fusion Devices
No full textAn accurate control of the magnetic boundary of a thermonuclear plasma is an important issue in magnetic confinement research.
The development of methods for the active control of magnetohydrodynamic instabilities and correction of error fields is mandatory
in view of fusion reactors or experimental test reactors under design. Recently, a very effective control scheme, named clean mode
control (CMC), has been proposed in a reversed field pinch experiment (RFX-mod). The CMC is based on the real-time correction
(cleaning), under simplifying hypothesis, of the sideband harmonics in the magnetic field produced by the discrete local active coils.
In this paper, we focus on the problem of carefully computing the penetration of sidebands through a realistic load assembly, but
still with a simplified cylindrical geometry, to allow for a detailed comparison with the crude CMC algorithm without the additional
complication of the coupling between the poloidal harmonics due to the toroidal geometry
Numerical modelling of electromagnetic loads on fusion device structures
No full textIn magnetic connement fusion devices, during abnormal operations (disruptions)
the plasma begins to move rapidly towards the vessel wall in a vertical displacement event
(VDE), producing plasma current asymmetries, vessel eddy currents and open eld line halo
currents, each of which can exert potentially damaging forces upon the vessel and in-vessel
components. This paper presents a methodology to estimate electromagnetic loads, on threedimensional
conductive structures surrounding the plasma, which arise from the interaction of
halo-currents associated to VDEs with a magnetic eld of the order of some Tesla needed for
plasma connement. Lorentz forces, calculated by complementary formulations, are used as
constraining loads in a linear static structural analysis carried out on a detailed model of the
mechanical structures of a representative machine
Computation of stationary 3D halo currents in fusion devices with accuracy control
No full textThis paper addresses the calculation of the resistive distribution of halo currents in three-dimensional structures of large magnetic confinement fusion machines. A Neumann electrokinetic problem is solved on a geometry so complicated that complementarity is used to monitor the discretization error. An irrotational electric field is obtained by a geometric formulation based on the electric scalar potential, whereas three geometric formulations are compared to obtain a solenoidal current density: a formulation based on the electric vector potential and two geometric formulations inspired from mixed and mixed-hybrid Finite Elements. The electric vector potential formulation is usually considered impractical since an enormous computing power is wasted by the topological pre-processing it requires. To solve this challenging problem, we present novel algorithms based on lazy cohomology generators that enable to save orders of magnitude computational time with respect to all other state-of-the-art solutions proposed in literature. Believing that our results are useful in other fields of scientific computing, the proposed algorithm is presented as a detailed pseudocode in such a way that it can be easily implemented
Lazy cohomology generators enable the use of complementarity for computing halo current resistive distribution in fusion reactors
No full textThis paper presents a methodology to efficiently calculate the resistive distribution of halo currents in 3-D conductive structures that surround the plasma in magnetic confinement fusion devices. The domain of the problem is so complicated that two complementary formulations are used to monitor the discretization error. It turns out that thousands of cohomology generators are needed by the electric vector potential electrokinetic formulation, which would require an enormous amount of memory and computing power to retrieve them even using state-of-the-art algorithms. To solve this challenging problem, we present a novel algorithm to generate the absolute second cohomology group generators exploiting the idea of lazy cohomology generators stored as sparse vectors. The proposed algorithm allows a saving of between four and five orders of magnitude computational time
A novel tool for breakdown probability predictions on multi-electrode multi-voltage systems
No full textAn innovative approach for the voltage breakdown prediction in high-voltage systems, insulated by large vacuum gaps, is presented. It is based on the correlation between the clump mechanism and a statistical approach to the breakdown probability. The aim of this paper is twofold. First, the numerical solution of 3-D electrostatic problems by a couple of complementary formulations is presented. Second, an efficient post-processing tool is introduced, based on the analytical solution of the equations of motion in a domain covered by a tetrahedral mesh, to estimate the breakdown probability associated to the electrically charged microparticles leaving one electrode and clashing to the electrode with opposite polarity with sufficient energy to get vaporization. This approach has been benchmarked on a reference configuration (sphere/plane) problem and applied to calculate the particle trajectories in a very complex multi-electrode multi-voltage system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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