Superconductors and applicability

In 1911, for the first time, scientists discovered that conductive matter with a completely non-resistive feature called it a superconductor. At this early stage, the newcomer knew of a characteristic of superconductors: that if an electric current was applied to a circuit made of superconducting material, the current would run in it forever without deterioration, because it did not Meet an impedance on the way, meaning that electrical energy is not consumed during the transmission of electricity from one place to another.

This is regarded as a form of permanent movement in electricity. This characteristic, called: The first characteristic of superconductors.

Electrical conductivity means that electrons separate from their atoms and move in the conductive crystalline structure (copper, aluminum, iron, etc.), when electrons collide with atoms on the way in the substance. electrical conductors produce resistors that cause power loss. The loss is up to 15% and 20%. Thus, if the application of superconductors to transfer power from power plants to consumers, will save a lot for society.

But the obstacle is that superconductors appear only at very low temperatures, only a few degrees above absolute zero (0 degrees K, which is minus 273 degrees Celsius); Specifically, the temperature that was recorded in the superconductor above is 23 degrees K and must use liquefied Helium gas for cooling, which is a complex and expensive substance, requiring the discovery of substances New superconductors, appropriate, overcome the above disadvantages.

American Physical Society (Photo: lci.ken)

- By January 1986 in Zurich, scientists Alex Muller and Georg Bednorz accidentally discovered a ceramic substance that constitutes elements: Lanthanum, Copper, Barium, Metal Oxide. This ceramic becomes superconducting at 35 degrees K.

Shortly thereafter, US scientists discovered ceramic substances that make superconductors at temperatures up to 98 degrees K. It is important that they cool with liquid nitrogen. It is a cheaper and easier to manipulate than liquid Helium. People call these new superconductors. This result stimulates scientists to scramble to find ceramics with superconducting properties at higher K temperatures to bring convenience and low cost of superconducting applications to life .

- In 1987, American Physical Society opened a Scientific Conference in New York with the presence of many famous physicists in the United States and many countries around the world. People exchanged new features of superconductors, one of which is the phenomenon of "ceramic hanging" discs suspended on magnets, which is called "the Meissner effect". This effect prevents the magnetic field from penetrating the superconductor surface, thus making the ceramic disc itself raised and hovering over the magnets; but if it is a strong magnetic field, it can still overcome the thrust, then it destroys the superconducting properties of the material. Thus, superconducting ceramics appear to be susceptible to strong magnetic fields. At the same time, the principle of Magnetic Levitation ( maglev ) is also mentioned, this principle relies on the magnetic field due to superconducting magnet plates produced when maintaining very low temperatures. At that temperature, all resistances are no longer magnets becoming superconductors and creating extremely strong magnetic fields.

Principle experiments Magnetic Levitation
(Photo: replogle-globes)

From the above results, along with other studies, it was concluded: Low-temperature superconductors can produce very strong magnetic fields and collectively, the second characteristic of superconductivity. Every superconductor makes a magnetic field; on the other hand, the current flowing in the superconductor does not encounter any resistance, so the superconducting magnetic field produces very strong. Thanks to that, humans can now create artificial magnetic fields 200 times stronger than the Earth's magnetic field.

- Also at this scientific conference, scientists also discussed the new invention of superfluid (it also works at very low temperatures, to the maximum limit of sound) and it has no grip. sticky, meaning there is no friction, if the action is spinning, they will not stop. This is also referred to as a permanent movement in liquid. From the above presentations, we can define: Superconductors are substances that exist at extremely low temperatures, when current flows without resistance. Both: superconducting and superfluid are attractive fields of contemporary physics, from here, they quickly realize their great potential. It must be said that, years ago, it was known that superconducting ceramic was a mixture made of metals, alloys, metal oxides such as copper (Cu), niobium (Nb) . in In the future, there will certainly be many other superior superconducting ceramic substances and the temperature will be high.

So far, the highest temperature achievable with a new superconducting ceramic is 125 degrees K. But the reality is that ceramic substances superconducted at temperatures higher than 100 degrees K are not stable because it quickly loses superconductivity. This is one of the major obstacles on the way to conquer superconductivity. The destruction of superconductivity when affected by strong magnetic fields is explained as follows: It is due to "magnetic vortex" (ie magnetic lines moving inside the material, such as whirlpools traveling in water ), these vortices move, creating electric fields that prevent electric current from moving freely, thus producing the superconductivity of the material.

- In addition to obstacles such as superconductors that appear only at low temperatures, and superconductors at temperatures higher than 100 degrees K are unstable; Another obstacle requires early overcoming, that is, superconductors are made in the form of a powder, which can be compressed into a solid but very brittle. For ease of application, we need to turn it into a "string", but the brittleness impedes this technical intent. However, based on the technology of microchip, people mimic that method and proceed as follows: Spraying this powder into a thin layer on the background of another material called substrate (ie, spreading the constituent elements). ceramic on the base). Thus it can be created into "seconds" and can bend the desired line on the plane. However, do not bend because it is easy to create short circuits.

- From the second characteristic of superconductivity has opened many directions of application and industrialists have been excited to jump into the hunt for new industry from superconducting. They target some of the following main application areas:

+ Based on "superconducting magnets", the Japanese and the Germans designed trains to run on magnetic pads. The Japanese have experimented with about 3-4 technology of ships running on different magnetic buffers, named Maglev based on: performing electric lifting - dynamics by creating two opposite magnetic fields between super magnets guide placed on the train and coils installed in concrete U-shaped rails.

High A Japanese ship with Speed ​​Surface transport system - HSST (Photo: bobbea)

The following is the most promising model tested for the third time, with specs: the train runs from Tokyo to Osaka, about 500km apart, aiming to carry 100 passengers in an hour. The magnetic field produced by superconducting magnets is strong enough to lift the ship 10 cm off the rail. The track has a U-shaped section, with 3 magnetic coils installed on it, powered by power stations located underground along the train. Superconducting magnets are placed on ships and placed in Helium containers that have liquefied, creating a low temperature of 269 degrees below zero, when an electric current passes, producing a magnetic field of about 4.23 tesla to lift the ship. up in the U-rail frame.

Thanks to the attraction and alternating repulsive force between the South-North poles of the second coil and the magnet, the ship moves forward. Speed ​​control by adjusting the frequency converter in the coil from 0 to 50 Hz and adjusting the remote speed at the control center. To stop the train, people do braking like on an airplane. The Japanese had to produce and test for 7 years with a budget of over 3 billion USD. The system is sometimes called the " High Speed ​​Surface transport " ( HSST ) system.

+ In the direction of this HSST technology, the Germans built the "Transrapid" ship running on magnetic padding and also followed the principle of inventing from the 1960s with slightly different Japanese technology, which is the method of electromagnetic lifting thanks to the impact of the magnet bars on the ship, with resistance magnets running underneath and on the T-shaped train lines. Estimating the speed of 450 km / hour running on Berlin to Hambourg, costing about 6 billion USD . In addition, the French are also concerned about the problem of super speed transport on the set by superconducting.

Scientist Alexei Abrikosov (Photo: hindu)

+ Another important application is that it is possible to create a powerful accelerator to study the original properties of atoms. People use powerful magnets to bend the beams, making them run in a circular way so they bump into each other, thereby studying the "fragments" generated by those strong bumps; It is called "superconducting superconductivity", based on this principle, American scientists are building a "powerful accelerator" in an 88-kilometer long tunnel in the state of Texec to study the Basic particles of matter.

- The third characteristic of superconductors is: If two superconductors are placed close to each other (but do not touch each other), electrons can jump through as if the two conductors are in contact. Where the current flows, it is called "Josephson coupling". But the current flowing through the joint is very sensitive to changes in the electric field and the external magnetic field. This helps scientists come up with the idea:

+ Can be used to produce an accurate electric field meter.

+ Another important application from this third characteristic of superconductors is that it is possible to make "electromagnetic circuit breaker" like a transistor. Along with the first characteristic is conductivity without being able to make the computer connected by "superconducting seconds", thus making the new generation "super-fast electronic computer" for research. Save space.

Scientist Vitaly Ginzburg
(Photo: derstandard)

+ In addition, Josephson coupling can be used to produce medical devices to study microscopic bioelectric fields produced by human brain activity, helping to diagnose brain diseases. Or thanks to the super magnet, it is possible to create medical MRI scanners (scanning images by measuring the echo of sounds) to examine tissues in the human body.

+ In addition to the aforementioned things, it is hoped that the results of superconductivity can be applied to create star-watching, planetary, or surface-observing devices and help explain the mechanism. of some strange objects in the universe, such as neutron stars, super-solid supernova objects of exploding stars before turning off, are thought to have the same rotation properties as liquid superconductors. .

- Recently, scientists Alexei Abrikosov, Vitaly Ginzburg (Russian) and Anthony Leggett (British-American) have contributed a lot to the field of superconducting theory and opened many directions with high technology applications in the computer field, super efficient power transmission . Their achievements were evaluated as second generation superconductors and three scientists were awarded the Nobel Prize for physics in 2003 . However, theoretically, it is still not possible to explain how superconductors actually work?

Scientist Anthony Leggett
(Photo: perimeterinstitute)

although its physical phenomena have been known not less.

- Talking about new superconducting materials, we cannot help but mention the recent success of Japanese people, that is, scientists from Aoyama University - Gakin in Tokyo have found superconducting materials from non-metallic type like Magnesium (Mg), or Bo (B) . What makes it so cheap is that the superconductor only works at temperatures - 133 degrees Celsius. America. This success is respectable, because it opens up to non-metallic semiconductors that are cheap materials, but the temperature to form superconductors is acceptable.

- In our country, research on superconductors has been done by scientists from Hanoi University in the past, now the National University of Hanoi, for nearly two decades (the author of the article) This 15 years ago visited the lab above). Our scientists cooled with liquid nitrogen and created some inexpensive superconductors. However, because there is no market yet, or rather the financial potential of the country is still limited, this high-tech field cannot be far ahead. Also at this school, the direction of "nanotechnology" in a very new and future field is also very early in the era. Funds are still the biggest barrier to developing those areas. Hope this obstacle is soon removed.