Massimo Guarnieri

An integral formulation for eddy current analyses in axisymmetric configurations

A method for solving problems of electromagnetic field diffusion in axisymmetric configurations with linear conducting media is presented. The approach, which is based on lumped-parameter circuit modeling, has a number of theoretical and practical advantages in comparison with other methods currently used, particularly in dealing with problems where the coupling between the magnet system and the external feed network is important. The authors describe in detail the analytical basis and the numerical approach of the method and present its most interesting aspects together with a discussion on a number of critical problems faced during numerical implementation. In order to show the methods capabilities and performance, some numerical results are given. >

A procedure for axisymmetric winding design under parametric constraints: An application to the RFX poloidal transformer

The problem of winding design to perform a specified field synthesis is usually carried out as analytic determination of current distribution within a given region. This approach may be useful for conceptual or preliminary design, but presents severe technical difficulties from a construction point of view. A construction oriented procedure for axisymmetric air core windings for fusion devices has been developed, to account for parametric constraints such as current per turn, current density, number of turns and diagnostic accessibility. Starting from a preliminary tentative design, presenting suitable electrical parameters, each coil position is automatically adjusted, within specified limits, to achieve the required field synthesis. A package has been implemented and succesfully applied to the RFX [1] Poloidal Field Transformer design and the main results are reported in the paper together with a number of numerical examples.

The RFX toroidal field winding design

The RFX toroidal field winding consists of 48 coils, which can be connected in many series/parallel configurations according to the toroidal field programming required for plasma operation. For ease of maintenance each coil consists of two identical half-coils connected at the equatorial plane of the machine. To be in alignment, the half coils are placed into grooves machined in an aluminum shell, which also has the function of withstanding the overturning moment caused by to the interaction between the current and the poloidal field. Stainless-steel clamping belts are provided around the coils to withstand their electromagnetic expansion forces and to keep them in the grooves. Thermal expansion of the half coils takes place freely along the grooves, due to thin layers of low-friction material placed on the coil surfaces. The demountable joints which connect the conductors of the half coils are designed to allow thermal expansion. Two basic alternative solutions considered for the electric contacts are discussed: the first based on a multicontact plug-in system, the second on bolted joints. >

CFD study on electrolyte distribution in redox flow batteries

The most important component in a redox flow battery (RFB) cell is the MEA (membrane electrode assembly), a sandwich consisting of two catalyzed electrodes with an interposed polymeric membrane. In order to allow electrolyte flow toward the electroactive sites, the electrodes have a porous structure that can be obtained with carbon base materials such as carbon felts. The RFB cell is closed by two plates containing the distribution flow channels. Considering that a uniform electrolyte distribution in the reaction region is a prerequisite for high-efficiency operation, the flow pattern is an important parameter to be investigated for the optimization of the cell.In the present work, the effect of different channels patterns on the electrolyte distribution and on the pressure drop is numerically investigated. Three-dimensional simulations have been carried out with ANSYS Fluent code and four different layouts have been considered. Calculations have been performed both in the distribution channels and in the felt porous region.

Current diffusion in the RFX magnetizing winding

RFX is a fusion Reversed Field Pinch (RFP) experiment under construction in Padua, Italy. Its air-core magnetizing winding is part of the poloidal-field winding and is devoted to inducing the toroidal plasma current by transformer action. This is obtained by slowly charging the winding to a specified current which is then forced to deca quickly. During this fast decay, the current density distribution inside each conductor behaves according to diffusion equations and this causes the transient stray magnetic field in the plasma region to rise well above the static value. A numerical approach, based on the volume integral formulation, is developed to study these diffusion phenomena. After a brief description of the mathematical basis of the method, the numerical analysis performed is presented and the stray-field evolution of a number of technical solutions considered to comply with the RFX design specifications are compared. >