Levitation with superconductors

Superconductividad.
Un poco de historia…

Self-portrait by Kamerlingh Onnes
AIP Emilio Segre Visual Archives

Kamerlingh Onnes, after liquefying helium for the first time in 1908, devoted his laboratory at the University of Leiden (Holland) to measuring the properties of matter from -271 °C to -259 °C. The measurement of electrical resistance was one of the properties that interested him most, and in 1911 he observed that the electrical resistance of mercury disappeared below a certain critical temperature. Soon after verifying the phenomenon in Pb and Tl, he realised that this was a new behaviour of matter appearing at low temperatures; he had just discovered superconductivity. For his work in low-temperature research, he was awarded the 1913 Nobel Prize in Physics.

In 1957, J. Bardeen, L. Cooper and R. Schrieffer enunciated their theory, known as BSC, which for the first time explained almost all the properties of superconducting materials and won the 1972 Nobel Prize in Physics. The BCS theory postulates that, in the superconducting state, there is an attractive interaction between electrons through deformations of the metal lattice that couple them into pairs (Cooper pairs). These pairs are capable of carrying current without electrical resistance.

In 1986, J.C. Bednorz and K.A. Müller, at IBM Laboratories in Switzerland, discovered superconductivity in ceramic materials and at temperatures above the limit. This result earned them the 1987 Nobel Prize in Physics and started a revolution in the field as materials were quickly found that were capable of working at temperatures above the boiling point of liquid nitrogen (-196 °C), which allows them to be cooled much more easily and economically. These families of materials, which are called high-temperature superconductors, SATs, have led to increased technological interest in developing new applications.

But what is superconductivity?

Zero resistance

When an electric current flows through a conductor wire, it heats up, as can be seen by the change in colour of the resistors in cookers or the filaments in light bulbs. This phenomenon, called the Joule effect, is due to electrical resistance and occurs because the electrons collide with the atoms of the material when they move. In a superconductor, the electrons form Cooper pairs that move through the material, synchronising with each other and with the oscillations of the atoms, which allows them to carry the electric current without resistance.

Meissner effect

A superconductor is not only capable of carrying electric currents without resistance, but can also shield magnetic fields, a phenomenon known as the Meissner effect. All superconductors can completely shield the magnetic field, up to a certain value called the critical field (BC). Some pass to the normal state with very low values of the field; these are type I superconductors. In others, called type II, the magnetic field, from a certain lower critical field (BC1), penetrates through thin tubes in the normal state containing a quantified magnetic flux, while the rest remains superconducting and remains as such until it reaches a higher critical field (BC2), which can be millions of times higher than the Earth’s magnetic field.

Applications of superconductors

Superconducting materials are at the basis of many applications in our society. These include

Generating and conducting electrical currents with very low energy losses

Superconducting cables can carry direct current without losses. When working with alternating current there are always energy losses, but they are orders of magnitude lower than in the case of conventional copper or aluminium conductors.

Superconducting cable manufactured by Sumitomo. Courtesy of SuperPower, Inc.

Superconducting cables are being installed in the electricity grid in various places. They make it possible to transport the same power with smaller cross-sections and lower energy costs, which benefits the environment.

Superconducting cables are being used to design motors, generators and transformers that are much smaller and lighter. This has opened up, for example, the possibility of designing propulsion motors for ships or their use in wind turbines.

Connections of a superconducting cable installed in Long Island. Courtesy of American Superconductors

The production of large magnetic fields

The fact that superconducting wires of less than 1 mm in diameter can circulate hundreds of Amperes without losses, makes them ideal for building and operating coils to generate very intense magnetic fields (greater than 2 Teslas). This characteristic is what allows them to be used in nuclear magnetic resonance equipment installed in hospitals or the large magnets used in particle accelerators such as CERN’s LHC.

CERN’s Large Hadron Collider ring.
Courtesy of CERN

Resonance of a person’s head

Magnetic resonance imaging system,
manufactured by Philips

New transport systems

The high magnetic fields that can be generated by superconductors have made it possible to build levitating trains that can reach speeds of up to 580 km/h, as friction with the track disappears. The first commercial line is scheduled to enter service in 2025 between Tokyo and Osaka.

In other cases, the ability to levitate a superconductor over a magnet is being used to build vehicles that levitate over a circuit of permanent magnets.

Vehicle based on superconductor levitation. Courtesy of Evico GmbH/IFW Dresden

Design of new electronic devices

Superconducting materials are also used in various high-performance electronic devices. The most common are the so-called SQUIDs, which can detect very small magnetic fields and are used in precision scientific instruments to measure various physical quantities.

They are able to detect magnetic fields induced by transmissions between groups of neurons in the brain and have started to be used to obtain magneto-encephalograms.

Electronic circuit showing a SQUID

What do we do at INMA?

Manufacture and characterisation of superconductors for electrical applications

At INMA we work on the development of superconducting materials for electrical applications and the compression of their properties. The material is manufactured, its electrical, magnetic and thermal properties are studied and numerical simulations are carried out to predict its behaviour.

Laser-induced zonal melting techniques are used to fabricate bars and coatings of high-temperature superconducting materials. This technology has been used to produce 1mm diameter rods that can carry more than a hundred amperes in liquid nitrogen.

Wires have also been made using the powder-in-tube technique, which consists of filling a metal tube with superconducting powder and drawing and laminating it, keeping a superconducting core inside.

Laser cutting of a textured superconductor to form meanders for a resistive current limiter meanders for a resistive current limiter

Prototype of a 600 A busbar developed at our Institute

Superconducting coils

Our Institute collaborated in the design, manufacture and commissioning of the first superconducting solenoidal coil manufactured in Spain.

Laser cutting of a textured superconductor to form meanders for a resistive current limiter

Use of superconductors in metrology

Our Institute has developed a voltage standard based on the Josephson effect, an effect that appears in weak junctions between two superconductors, and which improves 1000 times the accuracy of previous standards. Subsequently, a resistance pattern based on the quantum Hall effect using a superconducting coil and a cryogenic current comparator based on SQUID detectors has been developed.

Superconducting sensors

Work is currently underway to develop new X-ray detectors based on superconductors. One of their possible applications will be the new X-ray telescopes that the European Space Agency plans to put into orbit in the future.

Laser cutting of a textured superconductor to form meanders for a resistive current limiter

MORE INFORMATION

Centenary of superconductivity

Throughout 2011 and the first half of 2012, and within the framework of a project funded by the Spanish Foundation for Science and Technology (FECYT), the Obra Social de Ibercaja, Quantum Design and our own Institute, a series of activities have been organised to commemorate the Centenary of Superconductivity and for which a series of materials have been prepared and are available to all those interested in this subject.

Informative leaflet

Exhibition: “Centenary of superconductivity: The quantum world on a kilometre scale”

This exhibition consists of 10 panels that review the properties of superconducting materials, their main applications and some of the research lines developed in our Institute. These panels can be downloaded below.

 

Application

An application on superconductivity has been created for the Ibercaja Virtual Laboratory. It contains five exercises related to the applications of superconducting materials. This application has been created so that teachers of Secondary Education and Baccalaureate can work on some aspects of superconducting materials with their students. In the download area there are specific files with information for teachers. This application can be downloaded at http://www.ibercajalav.net/curso.php?fcurso=551&fpassword=lav&fnombre=0.5036634103012764

Videos about superconductivity

A video on superconductivity and superconducting materials has been included in the CSIC repository CIenciaTK.

You can download the videos from the following links:

Superconductivity:
http://www.cienciatk.csic.es/Videos/MATERIALES+SUPERCONDUCTORES+SUPERCONDUCTIVIDAD_25447.html

Superconducting materials:
http://www.cienciatk.csic.es/Videos/MATERIALES+SUPERCONDUCTORES+MATERIALES+SUPERCONDUCTORES_25448.html

Applications about superconductivity:
http://www.cienciatk.csic.es/Videos/MATERIALES+SUPERCONDUCTORES+APLICACIONES_25451.html

The levitation process:
http://www.cienciatk.csic.es/Videos/MATERIALES+SUPERCONDUCTORES+EL+PROCESO+DE+LEVITACION_25449.html

Superconductivity at INMA:
http://www.cienciatk.csic.es/Videos/MATERIALES+SUPERCONDUCTORES+%C2%BFQUE+HACEMOS+EN+EL+ICMA%3F_25450.htm

Press releases

On the occasion of the centenary of superconductivity, the Tercer Milenio supplement of Heraldo de Aragón published on 18 October 2011 the article: “Cien años de superconductividad”.

Instituto de Nanociencia y Materiales de Aragón