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ELECTROMAGNETIC COMPUTATIONS ON FUSION DEVICES - VARIOUS STRUCTURE SCHEMATIZATIONS IN THE NEXT EUROPEAN TORUS
No full textIDENTIFICATION OF NONCIRCULAR PLASMA EQUILIBRIA USING A NEURAL-NETWORK APPROACH
No full textA technique using a single hidden layer backpropagation neural network is described to establish a nonlinear mapping between a set of magnetic flux measurements and some shaping parameters of a non-circular plasma. The technique has been applied for the identification of limiter and X point equilibria in the ASDEX Upgrade geometry; the dataset of equilibria required for training and testing the neural network has been generated by means of an integrated use of a fixed and a free boundary MHD code. The average accuracy of the identification procedure is quite good, with a further improvement if a linear connection between the input and output layers is introduced. A procedure is also proposed for the selection of the optimum location of a limited number of sensors. The relationship existing between the behaviour of the neural network and some statistical parameters of the dataset is analysed and discussed
A MODEL-REDUCTION TECHNIQUE FOR HIGH-ORDER EDDY-CURRENT PROBLEMS
No full textA technique is presented which is based on the balancing of the dynamic system
resulting from an eddy current problem. The algorithm employed is suitable for reducing
high-order systems, as required when studying a geometrically complex current pattern. The
technique has been successfully applied to the reduction of the model for the study of the
vertical instability of the plasma in the ITER tokamak reacto
A NEURAL-NETWORK APPROACH FOR THE SOLUTION OF ELECTRIC AND MAGNETIC INVERSE PROBLEMS
No full textMultilayer neural networks, trained via the back-propagation rule, are proved to provide an efficient means for solving electric and/or magnetic inverse problems. The underlying model of the system is learned by the network by means of a dataset defining the relationship between input and output parameters. The merits of the method are illustrated at the light of three example cases. The first two samples deal with inverse electrostatic problems which are relevant for nondestructive testing applications. In a first problem, a boss on an earthed plane is identified on the basis of the map of potential produced by a point charge. In the second problem, the geometric parameters of an ellipsoid carrying an electric charge are identified. In both cases, database of simulated measurements has been generated thanks to the available analytical solutions. As a sample magnetic inverse problem, the identification of a circular plasma in a tokamak device from external flux measurements is carried out. The results achieved show that the method here proposed is promising for technically meaningful applications
ON THE NUMERICAL-SOLUTION OF THE NONLINEAR 3-DIMENSIONAL EDDY-CURRENT PROBLEM
No full textIn this paper we discuss the properties of the finite dimensional nonlinear systems relative to the numerical formulations of a class of three-dimensional electromagnetic field problems. These structural properties make us more confident on the results of the numerical calculations, since problems arising from multiple or even chaotic solutions are a priori excluded. Numerical procedures for the computation of transient and steady-state solutions are presented and applied. The error introduced by the finite element discretization is estimated making use of the properties of the dual electric and magnetic formulations
PERIODIC-SOLUTIONS OF NONLINEAR EDDY-CURRENT PROBLEMS IN 3-DIMENSIONAL GEOMETRIES
No full textIn this paper numerical procedures for the finite element computation of periodic steady-state nonlinear eddy currents in three dimensional geometry are presented and compared. The periodic solutions are computed by using two "static methods" and are compared with the solution obtained by the "brute force" method
ANALYSIS OF VERTICAL INSTABILITIES IN AIR CORE TOKAMAKS IN THE PRESENCE OF 3-DIMENSIONAL CONDUCTING STRUCTURES
No full textA fully three-dimensional eddy-current code is adapted to treat the problem of
control of the vertical instability in an air-core tokamak. A rigid model of the plasma
displacement is adopted. The definitions of stability margin and residual growth time are
generalized. Examples of passive stability analyses are presented in the limit case of zero
plasma mas
ADVANCES IN ELECTROMAGNETIC DESIGN OF FUSION DEVICES
No full textThe specification of the large magnets needed in future fusion reactors based on the tokamak concept is presented as an inverse electromagnetic problem. The influence of the eddy currents flowing in the metallic structure is illustrated. Currently used computational tools and related mathematical formulations are reviewed. The behavior predicted by the numerical models is in agreement with experimental measurements, as demonstrated by a campaign of code validation. Recent progress on the techniques for the identification of the plasma parameters and for the scenario optimization is presented
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