Superconducting magnets use type II superconductors to create stronger magnetic fields than standard electromagnets. They operate at low temperatures, allowing electrons to move freely without resistance, and are being researched for use in levitating rail systems and MRI machines.
A superconducting magnet is an electromagnet in which the coils are made of a type II superconductor. It can easily create constant magnetic fields of 100,000 Oersteds (8,000,000 amperes per metre). They produce stronger magnetic fields than standard iron core electromagnets and cost less to operate.
To understand what a superconducting magnet is, it is important to know a little about superconductivity. When some metals and ceramics are cooled from a degree range near absolute zero, they lose their electrical resistance. This temperature is called the critical temperature (Tc) and is different for each material. When there is no electrical resistance, electrons can roam freely throughout the material. The element can hold large amounts of current for long periods of time without losing energy as heat. This ability to hold an extreme electric charge is called superconductivity.
Most metals have some sort of interlocking atomic structure. Their electrons are held loosely, so they can move in and out of the twisted pattern easily. As electrons move, they collide with atoms and lose energy as heat. Metals are able to heat and conduct electricity very well because of this. This is why pots and pans and things like toaster ovens are constructed of metal.
In a superconductor, electrons travel in pairs and move between atoms, rather than colliding with them. When a negatively charged electron moves through the texture with positively charged atoms, it attracts those positive atoms. Another electron is drawn towards the resistance and pairs with the original electron. They are constantly breaking free and joining other electrons, but with little or no resistance. For this reason they do not lose heat and energy like standard metal.
Type II superconductors are the type used in the coils of a superconducting magnet. A type II superconductor reaches Tc at a lower temperature than type I superconductors. They have a smooth transition from the superconductor to their normal state within a magnetic field. These two characteristics allow them to conduct higher currents than type I.
A superconducting magnet can be used for magnetic levitation. In the Meissner effect, a superconducting disk is placed under a magnet and cooled with liquid nitrogen. The superconductor is open to accepting a charge because it is cooled, the magnet induces a current and thus a magnetic field in the superconductor and the magnet begins to fluctuate on that field.
Research is underway to use a superconducting magnet for a levitating rail system. It is also being considered for making small but powerful magnets in use for magnetic resonance imaging (MRI). Long-term plans include the discovery of materials capable of producing superconductivity without freezing. If this material is discovered, it will change the future of many fields, including transportation and energy production.
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