The Measurement and Modeling of the Levitation Force between Single-Grain YBCO Bulk Superconductors and Permanent Magnets

The levitation force between a single grain YBCO cylindrical bulk superconductor and a permanent magnet is investigated. The force measured both in zero field cooling and field cooling condition in the temperature range 20 K - 80 K is reported. The dependence of peak levitation force and power dissipation on the temperature is analyzed and the saturation of the peak force with increasing the critical current of the material is pointed out. A numerical analysis is also carried out for understanding the electrodynamics of the levitation mechanism. Good reproduction of the measured data is obtained and relevant observed phenomena, such as hysteresis of the levitation cycle at high temperature and saturation of the peak force at low temperature, are explained by means of the model. Characterization of the material in terms of critical current density in the field range 0 T - 0.5 T is also obtained by means of the numerical model by means of the fitting of the measured data

Electro-Thermal Behavior of Layer-Wound BSCCO Coils With and Without Insulation

In this work, the electro-thermal behavior of two layer-wound High Temperature Superconducting (HTS) coils, realized with and without electrical insulation, is compared. Both coils are wound from the same BSCCO tape, and have a very similar geometry, with the same number of turns and layers. A heat input is applied to both coils, by tuning the current supplied to resistive heaters realized through stainless steel tapes wound on the mandrel at the inner surface of both coils. The heaters are in contact with one full inner turn of the winding. The coils are cooled in a liquid nitrogen bath, and the heaters are supplied with a constant current. Then, the windings are charged until the tape critical current is exceeded, and the tests are repeated for different heat loads. The signals acquired through voltage taps, suitably soldered at the same locations in both windings, are compared at the same testing conditions. Finally, the electrical characteristic of the different layers of the coils is related to the temperature of the heater and of the various turns of the coil by means of a 1-D thermal model

The Measurement and Modeling of the Levitation Force between Single-Grain YBCO Bulk Superconductors and Permanent Magnets

The levitation force between a single-grain yttrium barium copper oxide (YBCO) cylindrical bulk superconductor and a permanent magnet is investigated. The force measured both in zero field cooling and field cooling condition in the temperature range 20-80 K is reported. The dependence of peak levitation force and power dissipation on the temperature is analyzed, and the saturation of the peak force with increasing the critical current of the material is pointed out. A numerical analysis is also carried out for understanding the electrodynamics of the levitation mechanism. A good reproduction of the measured data is obtained, and relevant observed phenomena, such as hysteresis of the levitation cycle at high temperature and saturation of the peak force at low temperature, are explained by means of the model. Characterization of the material in terms of critical current density in the field range 0-0.5 T is also obtained by means of the numerical model by means of the fitting of the measured data

Electromagnetic and thermal analysis of the induction heating of aluminium billets rotating in DC magnetic field

Conventional induction heating of aluminium billets is a widely used technique in industry. However it is characterized by a very poor energy efficiency. Using a novel electromagnetic set-up where the aluminium billet rotates in a transverse DC magnetic field produced by superconducting coils, the energy efficiency increases to interesting values. The paper studies the induction heating of aluminium billets in this new set-up. The analytical electromagnetic problem is revised in an original form, the heating transient is studied numerically and relevant parameters are estimated

An integrated approach to the control of magnetically confined plasmas

In this paper, a short review of the work done in the framework of a nation-wide research programme on 'Models and Methods for Plasma Control in Magnetically Confined Fusion Experiments' is presented. The broad aim of the overall programme is to develop and propose a new effective and reliable approach to the on-line plasma control for future fusion experiments, starting from the today's theoretical background, validated by experimental evidence from a number of tests performed on existing experiments. The proposed formulation to approach the control problem is a linearized model in terms of suitable state variables and input/output relationships. The basic project has been subdivided into four major areas of investigation: the linearized response plasma model, the three-dimensional electromagnetic model, the identification techniques and finally the plasma control requirements. The most remarkable results, achieved so far in each area above, are presented in the paper. (C) 2001 Elsevier Science B.V. All rights reserved