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Improving industrial prospects for new superconductor MgB2


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19.00 London BST/ 14.00 US EST
Wednesday 30 May 2001

The industrial prospects for Magnesium Diboride (MgB2), the common laboratory chemical turned superconductor 'discovered' in January this year, appear to be more encouraging following the demonstration that introducing internal structural defects could improve its performance in practical applications such as hospital Magnetic Resonance Imaging (MRI) scanners.

A team led by Professor David Caplin at the Centre for High Temperature Superconductivity at Imperial College, London, together with colleagues at the University of Surrey, report in the journal Nature today that inducing structural defects in MgB2, greatly enhances the material's ability to carry current in a magnetic field.

Their finding follows a report on 29 March 2001 also published in Nature by the Imperial team, that showed that whilst the current-carrying capacity of MgB2 is very high when there is no magnetic field - in strong fields, as are present in most applications of super-conductors - the performance is severely reduced. This seriously limits its suitability for use in medical and industrial applications such as MRI.

Professor Caplin explained: "In superconductors the ability to carry current without dissipation is enhanced if the material contains impurities or defects of suitable characteristics. This is counter-intuitive, in much the same way as an alloy, for example brass, that can be a lot stronger than the pure metal copper, in this analogy."

In an attempt to improve MgB2 the researchers decided to induce some disorder in MgB2 crystal lattice using the accelerator at the University of Surrey's Centre for Research in Ion Beam Applications (see notes to editor). They subjected samples of MgB2 to a series of proton irradiations of varying intensities in order to create a range of defect densities in the material.

Subsequent measurements by Dr. Yura Bugoslavsky, a senior scientist from the General Physics Institute, Moscow, currently visiting Imperial, established the optimum level of structural disorder (which maximised the current-carrying capacity in a high magnetic field) was one per cent.

Professor Caplin said that although their method of inducing defects in MgB2 by proton irradiation would be impractical for large scale manufacture superconductors, it is a significant step in its development as a superconducting material.

He said: "We've shown that modest disorder, at the level of about one per cent, which should be attainable in an economically viable way either by chemical doping or mechanical processing, can generate a material whose performance is technologically attractive."

He added that new alternatives to the traditional low temperature superconductors are desirable for a number of reasons.

"The low temperature superconductors have to be cooled to temperatures very close to absolute zero, and the cooling is very expensive. On the other hand, the high temperature super-conductors which were discovered 15 years ago, are cheap to cool to their operating temperature, but are difficult and expensive to fabricate.

"If MgB2 conductors themselves can be fabricated cheaply - the constituents are inexpensive - then because the cooling costs are modest also, several applications, for example, open-access medical magnetic resonance imaging magnets may become far more economically attractive," he said.

The multi-national scientific effort is reported in Nature this week alongside two other papers exploring the superconductivity of MgB2. One of these is from the University of Wisconsin-Madison (UWM), with which the Imperial group collaborate closely. The UWM group is headed by Prof. David Larbalestier, who is currently a Visiting Professor at Imperial, funded by the UK Engineering & Physical Sciences Research Council.

-ends-

For further information please contact:

Judith Moore
Press Office
Imperial College
+44 (0)20 7594 6702
j.h.moore@imperial.ac.uk

Notes to editors:

1. Title: Enhancement of the high-magnetic-field critical current density of superconducting MgB2 by proton irradiation.

Journal: Nature Vol. 411 - 31 May 2001

Authors: Y. Bugoslavsky (a), L. F. Cohen (b), G. K. Perkins (b), M. Polichettl (c), Y. J. Tate (b), R. Gwilliam (d), A.D. Caplin (b)

(a) General Physics Institute, 117942, Vavilov st38, Moscow, Russia.
(b) Centre for High Temperature Superconducivity, Blackett Laboratory, Imperial College, London SW7 2AZ, UK.
(c) INFM - Dipartimento di Fision, Universita di Salerno, via S. Allende, Baronissi, 1-84081 (Salerno), Italy.
(d) EPSRC Ion Beam Centre, University of Surrey, Guildford, Surrey, GU2 7RX, UK.

2. The accelerator at the University of Surrey's Centre for Research in Ion Beam Applications, speeds up charged particles, in this case protons (hydrogen atoms stripped of their orbiting electron) by applying a voltage of up to 2 million Volts. When an energetic proton hits the MgB2 sample, it penetrates a small fraction of a millimetre, but on the way it knocks magnesium or boron atoms out of their proper positions.

3. The College Centre for High Temperature Super-conductivity is an interdepartmental grouping of researchers from the Departments of Electrical and Electronic Engineering, Materials, Mathematics and Physics. Its web-site is www.ph.ic.ac.uk/CHTS/

4. Imperial College of Science, Technology and Medicine is an independent constituent part of the University of London. Founded in 1907, the College teaches a full range of science, engineering, medical and management disciplines at the highest level. The College is the largest applied science and technology university institution in the UK, with one of the largest annual turnovers (UKP339 million in 1999-2000) and research incomes (UKP176 million in 1999-2000). Web site at http://www.ic.ac.uk

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