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UAB Researchers Develop a Model for Optimising the Magnetic Levitation of Superconductors

October 01, 2002

A research team in the Physics Department at the UAB, formed by Àlvar S' nchez, Carles Navau (also lecturer and researcher at the Escola Universitaria Salesiana de Sarri' ) and Enric Pardo, have developed a complete theoretical model that allows for the detailed study of the magnetic force of levitation that appears in a high-temperature superconductor in the presence of a magnetic field.

Currently existing models are either incomplete or involve approaches that are simply not realistic. In contrast to these, the model that the UAB team has developed takes into account the so-called "de-magnetization effects", which appear when samples are finite (as opposed to the infinite samples used in non-realistic theoretical models). In addition to the force of levitation, the model provides a realistic description of equilibrium stability, that is, the resistance shown by the superconductor when subjected to a force that disrupts its position (this being a highly important consideration in the safety of MAGLEV trains) and of the energy used, in such cases, in returning to a position of equilibrium.

From their research, the scientists have drawn attention to a range of conclusions that establish the basis for the construction of future devices based on magnetic levitation: the demagnetizing effects that appear in thin superconductor samples can increase the force of levitation in a significant manner, whilst an excess of superconductor length need not imply an increase in force, and, in order to achieve good stability and equilibrium with small losses of energy, the current provided to the superconductor must be increased. The results of this research have been published in the journal Physical Review B and were presented at the Applied Superconductivity Conference, recently held in Houston, USA.

Magnetic Levitation

Magnetic levitation is one of the most characteristic and important properties associated with superconductors. Levitation has allowed for the construction of high-speed, magnetic levitation trains (MAGLEV). These types of trains, such as the German-built model ordered very recently for use in Shanghai, levitate over the rail tracks due to the forces of interaction between the magnetic fields produced by the magnets or coils located both on the train and on the rails. On levitating, the train is able to move without any contact being made between it and the rails, allowing it to reach very high speeds. The Shanghai train's magnetic fields are created by conventional electromagnets, but the future challenge lies in using superconductor materials; these would allow the flow of large amounts of current with only small energy loss. There is already a life-size prototype of these superconductor-magnet trains available in Japan, which has reached speeds of 550 kph. However, one of the problems facing these trains is that superconductor materials need to be cooled at very low temperatures (only a few degrees above absolute zero) in order to work. This problem may be resolved by using the high-temperature superconductors discovered in 1986.

Magnetic levitation also has applications in other technological ambits, such as energy storage, as it allows for the indefinite spinning of a superconductor wheel immersed in a magnetic field in such a way that it stores mechanical energy (this is known as a flywheel). These devices can store energy generated in electric power stations at a time of low electricity-consumption demand, to then be made available at peak periods. What these applications have in common is that they are based on the interaction of a superconductor with a magnetic field. In this way, a detailed understanding of this interaction becomes a key factor necessary to the design, production and improvement of real devices.

Barcelona, Universitat Autònoma de