Conectus - Superconductivity

SUPERCONDUCTIVITY

What is superconductivity and what can we expect from it ?

Superconductivity refers to a "macroscopic quantum phenomenon" which most materials exhibit at very low temperatures, and which is e.g. not dependent on nano-size structures. The superconducting state shows a number of extraordinary features: it allows, for example, a DC current to flow with no loss. Today strong superconducting magnets, exploiting this zero DC resistance, are routinely used in science, research and technological development (RTD) and in medical diagnosis, using Magnetic Resonance Imaging (MRI), the latter representing the biggest current market for superconductivity. In addition, the ultralow AC losses of superconductors may also result in potentially large energy savings in power applications, and demonstrations of power cables, transformers, motors or current limiters have already been made. Still another application is in exceedingly sharp, low noise microwave filters for base stations of radio communication systems. Finally, "Superconducting Quantum Interference Devices" (SQUIDs) based on weakly coupled so-called Josephson Junctions, enable us to monitor magnetic fields, which are more than a billion times weaker than the earth magnetic field, and made it possible to successfully record functions of the heart and the brain. These quantum interference effects have also been utilized in a new class of ultrafast, ultralow-power superconductor electronics, which in the future are expected to play an important role in areas, where traditional semiconductor electronics have reached its performance limit.

Thus the vast majority of existing or currently developed superconducting devices, no matter whether they are large scale or electronic devices, exploit, in one way or the other, the ultra-low losses of "super"-conductors. It should be noted, however, that if the operating temperature, the transport current or the magnetic field exceeds certain values which depend on the material and the fabrication process, then the superconductor looses this favourable property and becomes normal-conducting. Some devices actually take advantage of this feature or, more precisely of the extraordinarily strong non-linearities related to the superconducting-normalconducting transition of the material itself or of Josephson Junctions. Major technical features and their relevance to the various devices are briefly listed below. Several additional and very specific performance advantages or new functionalities are, of course, not addressed.

In summary, there are a number of components and systems in the different fields of electric power, industrial processing, transportation, medical applications as well as information and communication, in which superconductors offer unique functions.

Up to the eighties of last century superconductivity could only be utilized when the materials were held at very low temperatures (Low Temperature Superconductors, LTS). Then, in 1986, a new class of materials was discovered which show the transition to superconductivity already at higher temperatures (High Temperature Superconductors, HTS). The perspective of operating temperatures which need much less expensive and less complex cooling, raised hopes for a broad breakthrough of superconductor technology. However, the initially sometimes high-flying expectations ignored that the new materials are complex ceramics and the manufacture of superior devices needs highly controlled and reproducible process technologies. Since then discovery of novel superconductors continues. A superconductor which in several respects is somewhere between LTS and HTS is the Magnesium Diboride MgB2 which was discovered in 2001. More information about the current status of the different applications is presented under TECHNOLOGY