A magnet consists of a superconducting coil in which current flow generating a large magnetic field. In the superconducting state the current flows without any resistive loss. So there is no Joule heating which is one of the major problems in the fabrication of high field conventional electromagnets. For example, to produce a field of 100 KG by a conventional magnet needs energy input of about 1MW.
The superconductors which are used for this application should have high critical fields. The most widely used materials are type II superconductor’s like Nb - Ti and Nb2Sn compounds. Low temperature superconductors are being used for fabricating superconducting Quantum interference devices (SQUIDs) which are used to measure magnetic fields and in medical diagnostics. A typical SQUID system for sensing magnetic field is shown in Fig 23.
A high speed levitating train (550 km/hr) making use of a conventional liquid helium superconductor material has been tested in Japan. Superconducting ship propulsion system with liquid helium superconductors also have been successfully tested in Japan.
Magnetic separator
Another application related to the production of magnetic fields is in magnetic separation. Ordinary electromagnets have long seen used for the processing of coal and other mineral raw materials to remove impurities. By passing the crushed solid material through a magnetic field, magnetic particles in the material can be diverted and collected Fig 24. With high strength magnetic fields, this technique can also be used in other process such as the removal of toxic metals from water, and the recovery of metallic catalysts from chemical rectors.
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