Superconductivity: The Dawn of Maglev

If you’v­e been to an airport lately, you’ve probably noticed that air travel is becoming increasingly congested. Despite frequent delays, airplanes still provide the fastest way to travel hundreds or thousands of miles. The only alternatives to airplanes — feet, cars, buses, boats and conventional trains — are just too slow for today’s fast-paced society. However, there is a new form of transportation that could revolutionize transportation of the 21st century the way airplanes did in the 20th century. A few countries are using powerful electromagnets to develop high-speed trains, called maglev trains. Maglev is short for magnetic levitation, which means that these trains will float over a guideway using the basic principles of magnets to replace the old steel wheel and track trains. Well if maglev trains and Superconductors are really so awesome then why haven’t they been used widely? Let us first try to understand the problem with it.

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A Japanese Maglev Train. Image Courtesy- Capitalist Creations

Friction is a force that holds back the movement of a sliding or a rolling object. Well friction is more perfectly called as a ‘Necessary Evil’. Friction is something the prevents you from slipping as you walk, friction is something that saves your car from drifting or skidding off and yes it is the same friction that leads to loss of power during its transmission either mechanical, hydraulic or electric. Speaking of electric power, here the Friction is well pronounced as ‘Resistance’ which is defined as the obstruction offered to the flow of electric current in an conductor. Thus as we see resistance is not feasible when it comes to power transmission. Scientists have been working heavily to invent a composite with least resistance which can pave way for another E-Revolution.

One of the interesting things about resistance is how it changes as you change the temperature. Suppose you have a piece of gold wire in an electrical circuit. Gold is one of the best conductors there is: it shows very little resistance to electricity. But increase its temperature and it puts up much more resistance. Why? Broadly speaking, the higher the temperature, the more thermal vibrations there are inside the gold’s crystalline structure and the harder electrons (the negatively charged particles inside atoms that carry electric currents) will find it to flow through. Conversely, if you cool gold down, you reduce the vibrations and make it easier for electrons to flow. Thus we see that the superconductors are most likely to be found in the lower temperature regions.

Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature. A superconductor is diamagnetic: it refuses to let magnetism penetrate inside it. How does that work? Stand a superconductor in a magnetic field and you’ll make electric currents flow through its surface. These currents create a magnetic field that exactly cancels the original field trying to get inside the superconductor and repelling the magnetic field outside. This is known as the Meissner effect and it explains how you can make a superconductor levitate (float) in a magnetic field. The temperature thresholds are incredibly low, and thus incredibly expensive to maintain. Aluminum, for instance, has a superconducting temperature threshold of 1.2 Kelvin, or -271.95 °C.

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Levitation achieved by liquid nitrogen cooling. Image Courtesy-New Scientist

Superconducting magnets are some of the most powerful electromagnets known. They are used in MRI/NMR machines, mass spectrometers, and the beam-steering magnets used in particle accelerators. They can also be used for magnetic separation, where weakly magnetic particles are extracted from a background of less or non-magnetic particles, as in the pigment industries. Superconductors are used to build Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. Promising future applications include high-performance smart grid, electric power transmission, electric motors (e.g. for vehicle propulsion, as in maglev trains), magnetic levitation device and superconducting magnetic refrigeration.

Maglev (derived from magnetic levitation) is a transport method that uses magnetic levitation to move vehicles without touching the ground. With maglev, a vehicle travels along a guideway using magnets to create both lift and propulsion, thereby reducing friction by a great extent and allowing very high speeds. Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields. As mentioned already, a superconductor refuses to let magnetism penetrate inside it. Magnetic materials and systems are able to attract or press each other apart or together with a force dependent on the magnetic field and the area of the magnets.

The discovery of so-called high-temperature superconductors moved research on enormously. The original superconductors needed temperatures within a whisker of absolute zero—and you can reach those only by cooling materials using an expensive coolant gas such as liquid helium. But the high-temperature superconductors can be cooled using liquid nitrogen instead, which is about 10 times cheaper to produce. A lot of applications that weren’t economic suddenly became a whole lot more practical when high-temperature superconductors were discovered. The record is currently held by a material called mercury thallium barium calcium copper oxide, which superconducts at −135°C (−211°F or 138K) and was patented by Korean scientists in 1996.

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Propulsion in maglev trains. Image courtesy- R miller

What’s so good about superconductivity? Yes, you can make little bits of ceramics float if you make them really cold, but what else can you do? Imagine if we could make a material that was superconducting at room temperature. Our computers would work faster because they’d allow electric currents to flow more easily. We could make powerful electromagnets that turned electricity into magnetism without wasting anything like as much energy. That would mean electric appliances in our homes and offices would waste much less power. We could also make “Maglev” (magnetic levitation) trains that would float on rails using linear motors and get us around with a fraction of the power used by current locomotives.