Superconductors cooling

A magnet hovers above a superconductor, cooled by liquid nitrogen. 

Efficiency, the word crops up virtually every time superconductivity is mentioned, and it is not difficult to see why. Efficiency, after all, is simply doing more with less effort, and when a superconductor carries electricity with no resistance and essentially no loss—and, theoretically, forever without any decrease in flow—that s efficiency of a most enviable kind. And although the transition from conventional superconductors cooled with liquid helium to the new high-temperature ceramics cooled with liquid nitrogen would not improve superconductivity—how, after all, can one make a perpetual motion machine more perpetual —it would dramatically lower costs, simplify refrigeration systems, and improve the reliability of just about everything electric in which the ceramics are used. 

Fig. 5.1 Magnet levitating above an 3mrium-containing superconductor cooled with liquid nitrogen. Source Mai-Linh Doan, via Wildmedia Commons, undta- lieense CC BY-SA 3.0. No changes made. Link http //commons.wikimedia.Org/wild/File Meissner effeet pl390048.jpg...

Superconductivity The physical state in which all resistance to the flow of direct-current electricity disappears is defined as superconductivity. The Bardeen-Cooper-Schriefer (BCS) theoiy has been reasonably successful in accounting for most of the basic features observed of the superconducting state for low-temperature superconductors (LTS) operating below 23 K. The advent of the ceramic high-temperature superconductors (HTS) by Bednorz and Miller (Z. Phys. B64, 189, 1989) has called for modifications to existing theories which have not been finahzed to date. The massive interest in the new superconductors that can be cooled with liquid nitrogen is just now beginning to make its way into new applications. 

A superconductor. A pellet of superconducting material, previously cooled to 77 K with liquid nitrogen, floats above a magnet. 

Superconductors have the ability to levitate vehicles with embedded magnets. This picture shows an experimental zero-friction train in Japan, built to use helium-cooled metal superconductors. 

Superconductivity is the loss of all electrical resistance when a substance is cooled below a certain characteristic transition temperature (Ts). It is thought that the low temperatures are required to reduce the effect of the vibrations of the atoms in their crystalline lattice. Superconductivity was first observed in 1911 in mercury, for which Ts = 4 K. Over the years, many other metallic superconductors were identified, some having transition temperatures as high as 23 K. However, low-temperature superconductors need to be cooled with liquid helium, which is very expensive. To use superconducting devices on a large scale, higher transition temperatures would be required. 

Fe(CN)6]3-(aq) + 6 H20(1). substrate The chemical species on which an enzyme acts, superconductor An electronic conductor that conducts electricity with zero resistance. See also high-temperature superconductor. supercooled Refers to a liquid cooled to below its freezing point but not yet frozen, supercritical fluid A fluid phase of a substance above its critical temperature and critical pressure. supercritical Having a mass greater than the critical mass. 

Superconductivity has been known since 1911, and superconducting systems based on various metal alloys (e.g., NbTi and Nb3Sn) are currently used as magnets and in electronics. These materials exhibit superconductivity only at temperatures below 23 K and require cooling by liquid helium. The discovery of ceramics that exhibit superconductivity at temperatures up to 120 K, the so-called high-temperature superconductors, has sparked a tremendous amount of scientific activity and commercial interest around the world. 

Flexible superconducting tapes provide promise of uses for superconductors in motors, generators, and even electric transmission lines. Meanwhile, superconducting magnets cooled to the temperature of liquid helium already are in use. High-field nuclear magnetic resonance (NMR) spectrometers have become standard instruments in chemical research laboratories, and the same type of machine (called an MRI spectrometer) is used for medical diagnosis in hospitals worldwide. 

Tunneling electric current through the normal metal insulator superconductor junction is accompanied with heat flow out of normal metal when property voltage is biased. The phenomenon enables cooling of electrons and phonons (under special conditions) in the region below 1K. At lower bath temperatures, two parasitic heat sources decrease refrigerator performance ... 

The commonly accepted pulsar model is a neutron star of about one solar mass and a radius of the order of ten kilometers. A neutron star consists of a crust, which is about 1 km thick, and a high-density core. In the crust free neutrons and electrons coexist with a lattice of nuclei. The star s core consists mainly of neutrons and a few percents of protons and electrons. The central part of the core may contain some exotic states of matter, such as quark matter or a pion condensate. Inner parts of a neutron star cool up to temperatures 108iT in a few days after the star is formed. These temperatures are less than the critical temperatures Tc for the superfluid phase transitions of neutrons and protons. Thus, the neutrons in the star s crust and the core from a superfluid, while the protons in the core form a superconductor. The rotation of a neutron superfluid is achieved by means of an array of quantized vortices, each carrying a quantum of vorticity... 

The Loss of Electrical Resistance. As mentioned previously, a superconductor displays an abrupt change in resistivity when it is cooled below the critical temperature. 

For example, in 1911, Dutch physicist Heike Kamerlingh Onnes cooled some mercury to the hoiling point of liquid helium 4 K. He found that at this low temperature, the mercury developed an astonishing property. The super-cooled mercury had zero resistance when an electric current passed through it. In other words, none of the energy of the electrical current was given off as wasted heat. The mercury had become a superconductor—a material with no resistance to electric current. 

The results were promising, but did not last long because of the discovery of inorganic ceramics. The ceramics displayed superconductivity without any cooling (Vanderah 1992). Nevertheless, organic metal and superconductors have their advantages, and investigation is carried out in this direction. 

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