Simone Minucci

Electromagnetic Models of Plasma Breakdown in the JET Tokamak

This paper presents the electromagnetic modeling of the plasma current breakdown phase of the JET tokamak. The first part of this paper models the presence of the JET iron core up-down asymmetry and the effects of the eddy currents in the reconstruction of the magnetic topology needed for the plasma start. The second part describes the approach used to evaluate the ionized particle connection length inside the vacuum chamber at breakdown. The results obtained are validated using JET experimental measurements.

The European DEMO fusion reactor: Design status and challenges from balance of plant point of view

DEMO initial conceptual design studies are being conducted in Europe as part of the European Union Roadmap to Fusion Electricity, which aims to demonstrate the feasibility of electricity produced by nuclear fusion reactors around the middle of this century. The aim of this paper is to provide an overview of the DEMO project, highlighting its main characteristics and challenges in terms of design, integration, and operation. Particular emphasis is given on some important systems of the Balance of Plant (BoP), such as the primary heat transfer systems, the related power conversion systems, and the electrical power plant. The relevance of such systems is due to the need of a continuous reanalysis at any significant design change because of their huge dimensions, technical complexity, and strong impact on design integration, maintenance, and safety.

Accuracy Assessment of Numerical Tracing of Three-Dimensional Magnetic Field Lines in Tokamaks with Analytical Invariants

Abstract We consider the problem of the accurate tracing of long magnetic field lines in tokamaks, which is in general crucial for the determination of the plasma boundary as well as for the magnetic properties of the scrape-off layer. Accurate field line tracing is strictly related to basic properties of ordinary differential equation (ODE) integrators, in terms of preservation of invariant properties and local accuracy for long-term analysis. We introduce and discuss some assessment criteria and a procedure for the specific problem, using them to compare standard ODE solvers with a volume-preserving algorithm for given accuracy requirements. In particular, after the validation for an axisymmetric plasma, a three-dimensional (3-D) configuration is described by means of Clebsch potentials, which provide analytical invariants for assessing the accuracy of the numerical integration. A standard fourth-order Runge-Kutta routine at fixed step is well suited to the problem in terms of reduced computational burden, with extremely good results for accuracy and volume preservation. Then we tackle the problem of field line tracing in the determination of plasma-wall gaps for a 3-D configuration, demonstrating the effective feasibility of the plasma boundary evaluation in tokamaks by tracing field lines with standard tools.

Survey of electric power supplies used in nuclear fusion experiments

Nuclear fusion could ensure a large-scale, safe, environment-friendly and virtually inexhaustible source of energy. A nuclear fusion facility can be considered as a complex electrical machine with many power supplies and electrical systems. This paper presents a survey of the main features of the power supplies in nuclear fusion facilities (tokamaks). The main characteristics in terms of nominal ratings, operational parameters and performances are shown and compared for many experiments, as ITER, JT-60SA, EAST, KSTAR, JET, ASDEX, FTU and DTT.

On the Influence of Channel Tortuosity on Electric Fields Generated by Lightning Return Strokes at Close Distance

In this paper the results of the estimated electric field associated with tortuous lightning paths at close distance (50 m to 500 m) are shown. Such results are compared with experimental data available in the literature and are illustrated along with a quantitative analysis of the field waveforms and their frequency spectra. The limits of the usual straight-vertical channel assumption and the influence of tortuosity at different azimuth and distances from the lightning channel base are also highlighted.

A strategy for the optimal choice of the magnetic sensors for the estimation of plasma parameters with fault tolerance in the ITER tokamak

In a tokamak, magnetic sensors are the primary diagnostics used to estimate the quantities controlled in feedback by the plasma current, position and shape controller. As a consequence, the number and position of the magnetic sensors has a large impact on the performance of the magnetic control system and on the tokamak configuration. In this paper, we consider the problem of choosing an optimal set of magnetic sensors for the ITER tokamak. As performance index we consider the capability of reconstructing the first plasma current density moments. Indeed a good reconstruction of these parameters guarantees also a good reconstruction of the parameters usually controlled by the magnetic control system (e.g. plasma-wall gaps, position of the current centroid, plasma current, etc.). The problem of choosing the best set of magnetic sensors is converted in a suitable convex optimization problem. Our approach allows us also to evaluate the level of redundancy in a given set of magnetic sensors and hence it gives information on how to behave in case of sensor faults. Numerical simulations are included in order to show the effectiveness of the approach.

Numerical behavior of models of composite materials in E'NDT at "Low" frequencies

Introduction In this paper the numerical modelling of composite materials in view of non-destructive testing (NDT) is considered. The numerical modelling is critical especially in the “low-frequency” regime because of a strong ill-conditioning of the relevant stiffness matrix. The proposed numerical model is robust with respect to this underlying ill-conditioning. The conductivity of new composite materials, specifically Carbon Fiber Reinforces Polymers (CFRPs), is reasonably high for allowing nondestructive evaluation based on eddy currents testing. However, the complex electrical structure of the CFRP composites, characterized by higher electrical conductivity along the direction of the carbon fibers and lower conductivity perpendicular to the fibers, poses very difficult problems for their electromagnetic description and modelling. The classic electromagnetic models based on the magnetic (electric) field integral equations, may fail to provide the correct solution at low frequencies such as those of NDT applications [1], [2], [3]. This is due to the low-frequency break-down problem consisting of a strong ill-conditioning of the relevant stiffness matrix. This strong ill-conditioning is due to the different scaling of the solenoidal and non-solenoidal components of the unknown fields, w.r.t. the frequency.