1,720,969 research outputs found
Modeling of MHD instabilities in existing and future fusion devices in view of control
Full text linkIn this thesis, an improved version of the CarMa code is presented, called CarMa-D, for the analysis of ResistiveWall Modes (RWMs) in thermonuclear fusion devices, simultaneously considering the effects of volumetric threedimensional conducting structures and in presence of the effects associated with plasma dynamics, toroidal rotation or drift-kinetic damping.
The CarMa-D code is the result of the coupling of the CARIDDI code, for the eddy current analysis in the conducting structures, with the MARS-K code, for MHD stability computations. The strength point behind CarMa-D is that the new coupling strategy does not rely on the simplifying assumptions of neglecting the plasma mass, toroidal rotation and kinetic damping physics, assumptions on which relies the CarMa code. Under these hypothesis, the plasma response to external perturbations depends on the dynamic of the perturbation itself: this behaviour is modelled through a matrix-based Padé rational function. The approximated plasma response is then combined with the equation for the eddy current induced in the metallic structures, in order to obtain a linear system of differential equations as the original CarMa version, but with a higher number of degrees of freedom to model the dynamics of the plasma. The new version overcomes the main limitations of the original computational model, in particular: (i) the massless assumption for the plasma is removed, allowing modeling of global modes growing on ideal-kink time scales; (ii) the effects of toroidal plasma flow and drift kinetic damping can be rigorously included into the new model, providing a powerful tool to study macroscopic phenomena where both plasma dynamics and 3-D conducting structures play important roles. The mathematical model has been also generalized to take into account multiple toroidal mode numbers (multi-modal CarMa-D). The code has been successfully tested with a reference equilibrium of a plasma with circular cross-section, and then used to study RWM stability analysis of the modes n = 1 and n = 2 on JT-60SA Scenario 5.
Finally, additional effort has been made to write the CarMa-D mathematical model in a way suitable for a state-space representation, in order to exploit its features in a model-based feedback control strategy to actively suppress RWMs
Matrix Based Rational Interpolation for New Coupling Scheme Between MHD and Eddy Current Numerical Models
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Model order reduction of large-scale state-space models in fusion machines via Krylov methods
No full textThis work presents a robust technique, based on Krylov subspace method, for the reduction of large-scale state-space models arising in many electromagnetic applications in fusion machines. The proposed approach, built on the Arnoldi algorithm, aims at reducing the number of states of the system and lowering the computational effort, with a negligible loss of accuracy in the numerical solution. A detailed performance study is presented on an ITER-like machine, addressing both 2D and 3D problems
Model-based approach for magnetic reconstruction in axisymmetric nuclear fusion machines
No full textThis paper describes an approach for the magnetic reconstruction of large-scale tokamak devices that is suitable for real-time employment in order to provide reference for active control action during the whole plasma evolution. This problem can be seen as a free boundary problem, where the shape features of the plasma are determined by the equilibrium with the external sources, namely, the active circuit currents and the eddy currents flowing in the passive structures. In this respect, a dynamic model is needed to estimate the induced currents and provide a consistent representation of the whole system behavior during the entire plasma discharge. Such a model is then coupled with an iterative optimization procedure to provide a model of the plasma that, superimposed with the external sources, minimizes the error of the reconstructed magnetic map with reference to the available sensor measurements. The analysis and validation of this approach are presented, resulting in a procedure that appears to accurately follow the behavior of the system during both slow varying evolution and strongly dynamic events
An Effective One-shot Body Part Multi-View Reconstruction Device with Self-calibration Capabilities
Full text linkThis paper introduces a custom-built low-cost camera ring device designed for automatic cast synthesis, able to accurately and instantly scan body parts. The scanned mesh will be used as a backbone model for the cast design and 3D printing. The system is based on the multi-view active stereo principle and it is composed of a circular array of 16 synchronized cameras (Fig. 1) and 4 equally distributed IR pseudo-random laser pattern projectors. We employ a custom multi-view stereo reconstruction pipeline based on (Schönberger et al., 2016), which guarantees optimal results without the downsides of the supervised data-driven multi-view stereo algorithms, i.e. data collection and ground truth labeling. Additionally, inspired by (Duda and Frese, 2018), we propose a novel, automated calibration system to extract intrinsic and extrinsic camera parameters which are required to perform robust multi-view stereo reconstructions
Efficient Numerical Solution of Coupled Axisymmetric Plasma Equilibrium and Eddy Current Problems
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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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