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New advance towards superconductor wires

March 22, 2004

Researchers at the Universitat Autònoma de Barcelona, the Materials Science Institute of Barcelona (ICMAB-CSIC), and various German and North American institutions have developed a simple method for measuring the maximum current that coated superconductors can carry. The material will, most likely, be used to manufacture the superconductor wires of the future. The research has been published in the journal, Applied Physics Letters.

Electric currents pass through superconductor materials without resistance, which is a property with many technological applications, but this is only possible when the materials are cooled below a certain temperature and when the current does not exceed a certain value.

The superconductor materials that will, most likely, be used for wires that transport electric energy are called coated conductors. They are formed by the deposition of a film of high-temperature superconductor material on a metallic band. The main advantage with respect to other types of superconductors is that they allow large quantities of electric current to move through them without the need for excessive cooling, yet they keep their superconductor qualities. This makes possible, among other things, the generating of highly intense magnetic fields with lighter superconductors and the transmission of electric current with minimum losses.

The principal limitation of these new generation materials is, however, that their microscopic structure is in the form of small grains, which limits movement through them and makes it more difficult, in each case, to know what the maximum current is that the material can carry and still maintain its characteristics of superconductivity. This information is indispensable for engineers who work on practical applications.

A team of scientists at the Materials Science Institute of Barcelona (ICMAB-CSIC) and of the Physics Department at the Universitat Autònoma de Barcelona, working with the Reference Centre for Advanced Materials for Energy (CeRMAE) of the Generalitat de Catalunya, together with researchers from the Zentrum fur Funktion Wekstoffe in Göttingen (Germany), the IFW in Dresden (Germany) and the Oak Ridge National Laboratory (United States), have developed a simple method for measuring the maximum current (called critical current) that coated superconductors can carry. The difference from other methods is that the new technique is non-invasive, i.e., it is not necessary to enter into contact with the material to measure its critical current.

The method developed by the team of researchers is based on measuring the response of the coated superconductor to the application of magnetic fields. The material undergoes a magnetic field with cyclical variations so that different maximum values are obtained; the method makes it possible to measure its critical current. Therefore, the new technique will allow engineers to calculate, in a simple way, the maximum intensity of electric current that a superconductor wire can carry without superconductivity being lost. Furthermore, the results obtained will make it possible to analyse how to improve the granular structure of the superconductor material so as to increase the current that can move through it, thereby obtaining the values required in applications such as superconductor wires for the transmission of electricity, new motors, more efficient and lighter generators, magnetically levitated trains or magnetic resonance image-generating apparatus for the human body for hospitals.

The research, led by the investigators Xavier Obradors and Teresa Puig (ICMAB-CSIC) and Àlvar S'¡nchez (UAB), has been published in the weekly journal, Applied Physics Letters.

Barcelona, Universitat Autònoma de