Superconductivity and Levitation

The superconductivity group at Tel Aviv University, led by physics Prof. Guy Deutscher, released this fascinating video of some results of their work. They are studying the mechanism of superconductivity in high temperature superconductors. They also want to make the physics of superconductors accessible and exciting for students and adults through the unique and counter-intuitive phenomena presented in this video. I think they are doing just that. This is fun to watch.

What is Superconductivity?

I will keep this simple. Additional in-depth background on superconductivity is here.

The flow of electric charge through conductors is affected by the temperature of the conductor, among several other factors. The flow of charge is called the current. Current is measured in units of amperes, or amps for short.

For most conductors such as metal wire, as the temperature is cooled, the conductor offers less resistance to the flow of charge. Consequently, the cooled conductor will allow more amps of current to flow through it. You might have studied the relationship known as Ohm’s Law. It describes the relationship of voltage, resistance, and current in electric circuits.

Some materials such as lead and mercury exhibit an abrupt new behavior when they are cooled to extremely low temperature by liquid Helium to about 4 degrees above absolute zero. Their resistance to electric current flow drops to zero. (Vertical line in the graph.) If there is no resistance, large amounts of current can flow without producing heat. The critical temperature (Tc) that prompts this superconductive property was discovered in 1911 by Heike Kamerlingh Onnes.

He studied the properties of materials at liquid helium temperatures, and discovered that metals such as lead and mercury lost all resistance when cooled to such temperatures, a phenomenon known as superconductivity (1911). Kamerlingh-Onnes was elected to the Royal Academy of Sciences in Amsterdam and received the Nobel Prize in physics in 1913 “for his investigations on the properties of matter at low temperatures which led, inter alia, to the production of liquid helium.”

Advances in Superconductivity

The production of liquid Helium is expensive and difficult. Keeping it cold is a challenge. There has been an interesting search in the past 100 years for materials that would exhibit superconductivity at warmer temperatures. The holy grail would be to achieve superconductivity at room temperature requiring no expensive or technically difficult cooling.

Superconducting metals, alloys and compounds were discovered. In 1941 niobium-nitride was found to superconduct at 16 K. In 1953 vanadium-silicon displayed superconductive properties at 17.5 K. And, in 1962 scientists at Westinghouse developed the first commercial superconducting wire, an alloy of niobium and titanium (NbTi). High-energy, particle-accelerator electromagnets made of copper-clad niobium-titanium were then developed in the 1960s at the Rutherford-Appleton Laboratory in the UK, and were first employed in a superconducting accelerator at the Fermilab Tevatron in the US in 1987. Then, in 1986, a truly breakthrough discovery was made in the field of superconductivity. Alex Müller and Georg Bednorz (above), researchers at the IBM Research Laboratory in Rüschlikon, Switzerland, created a brittle ceramic compound that superconducted at the highest temperature then known: 30 K. What made this discovery so remarkable was that ceramics are normally insulators. They don’t conduct electricity well at all. So, researchers had not considered them as possible high-temperature superconductor candidates. The Lanthanum, Barium, Copper and Oxygen compound that Müller and Bednorz synthesized, behaved in a not-as-yet-understood way.

Researchers around the world began “cooking up” ceramics of every imaginable combination in a quest for higher and higher critical temperatures, Tc. In January of 1987 a research team at the University of Alabama-Huntsville substituted Yttrium for Lanthanum in the Müller and Bednorz molecule and achieved an incredible 92 K TcFor the first time, a material had been found that would superconduct at temperatures warmer than liquid nitrogen, a commonly available coolant.

The Meissner Effect

A great step in understanding how matter behaves at extreme cold temperatures occurred in 1933. German researchers Walther Meissner and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field. A magnet moving by an ordinary conductor induces currents in the conductor. This is the principle on which the electric generator operates. But, in a superconductor the induced currents exactly mirror the magnetic field that would have otherwise penetrated the superconducting material. That mirroring magnetic field causes the magnet to be repelled. This is known as the “Meissner effect“. The Meissner effect is strong enough that a magnet can actually be levitated over a superconductive material. This short video will demonstrate the effect.

This video shows the Meissner Effect only occurs after cooling the superconducting wafer below Tc with liquid Nitrogen. At 40 sec, it expels the magnetic field of the cubical permanent magnet from the region of the ceramic wafer causing the magnet to levitate.

Students at the Nation Cheng Kung University in Tainan present the effects very clearly in this longer 6 minute video. Advance to 1:13 to get to the heart of the presentation. They show the Meissner Effect, Levitation and Suspension, and the Flux Trapping Effect. Viewing this really helps explain some of the behaviors in the previous videos.

A Little More Physics Fun

Will Room Temperature Tc Ever Be Reached?

The search continues for that goal. Whether reports such as the following are valid remain to be verified. It is up to the scientific community to review the claims. On July 29, 2013, it was claimed that magnetization tests showed a small amount of a compound consistently produced the Meissner effect near 38˚ Celsius. My house temperature is 78˚ F today. That is 25˚ C. If the claims are true, it would be a welcomed result. Advances are being made toward the room temperature Tc. Engineering viable and economic solutions with these new technologies and compounds is years in the future. One more reason to keep those research and development dollars flowing.

Superconductivity Uses

Magnetic-levitation is an application where superconductors perform extremely well. Trains can be made to “float” on superconducting magnets virtually eliminating friction between the train and its tracks. Conventional electromagnets waste much of the electrical energy as heat. They are physically much larger than superconducting magnets. Commercial use of MAGLEV technology occurred in 1990 with a nationally-funded project in Japan. The Yamanashi Maglev Test Line opened on April 3, 1997. In December 2003, the MLX01 test vehicle attained an incredible speed of 361 mph (581 kph). Here is a video sample of that train called Chūō Shinkansen.

During a high-speed rail outreach trip to Japan May 11-12, 2010, U.S. Secretary of Transportation Ray LaHood experienced firsthand Central Japan Railway’s cutting edge high-speed rail technology, the same technology JRC hopes to bring to the Baltimore–Washington and the Northeast Corridor in the near future.  Secretary LaHood, accompanied by JRC’s Chairman, Yoshiyuki Kasai, rode on JRC’s Superconducting MAGLEV (SCMAGLEV)–the world’s speed record holder at 581km/h (361mph).  At a press conference held at the conclusion of his visit with JRC, Secretary LaHood commented that, “We (the U.S.) are right at the beginning of an opportunity for American cities to be connected by high-speed trains,” and further said that he was, “. . . delighted with this opportunity to really experience all the technology.”

A search for current proposed maglev rail projects in the U.S. yielded little of news that was up to date. Most projects are on hold due to funding constraints and the slowness of the Federal Environmental Impact Statements. Whatever excuses are used, the fact remains that U.S. is not moving significantly in the direction of maglev transportation. The world’s first MAGLEV train in commercial service was a shuttle in Birmingham, England. It shut down in 1997 after operating for 11 years. A China-German maglev is currently operating over a 30-km course at Pudong International Airport in Shanghai, China.

Superconductors can perform a life-saving function in the field of biomagnetism. By using a strong magnetic field directed into the body, hydrogen atoms in our water and fat molecules are forced to accept energy from the magnetic field. They release this energy at a frequency that can be detected and displayed graphically by a computer. Magnetic Resonance Imaging (MRI) was discovered in the mid 1940’s. But, the first MRI exam on a human being was not performed until July 3, 1977. It took five hours to produce one image. Today’s faster computers have shortened that time. Lots more MRI info here.

The MRI machine makes loud humming, tapping, and buzzing noises. Earplugs may help lessen the noises made by the MRI machine. Some facilities let you listen to music during the test. You will need to remain very still during the test. Any movement may blur the pictures. If you’re unable to lie still, you may be given medicine to help you relax.

You may be asked to hold your breath for 10 to 15 seconds at a time while the technician takes pictures of your heart. Researchers are studying ways that will allow someone having a cardiac MRI to breathe freely during the exam, while achieving the same image quality.

The one event responsible for putting “superconductors” into the American lexicon was the Superconducting Super-Collider project planned for construction in Ellis county, Texas. Congress cancelled the effort in 1993. The high-energy collider would never have been possible without superconductors. CERN, a consortium of several European nations, is doing something similar with the Large Hadron Collider (LHC) along the Franco-Swiss border. A proton-antiproton collider was formerly operating using superconducting magnet technology at Fermilab. It was used to discover the Top quark and lay the groundwork for the announcement of the Higgs boson at CERN. Fermilab was the first collider facility to use superconducting magnets.

According to Superconductors.org …
Electric generators made with superconducting wire are far more efficient than conventional generators wound with copper wire. In fact, their efficiency is above 99% and their size about half that of conventional generators. These facts make them very lucrative ventures for power utilities. Other commercial power projects in the works that employ superconductor technology include energy storage to enhance power stability. American Superconductor Corp. received an order from Alliant Energy in late March 2000 to install a Distributed Superconducting Magnetic Energy Storage System (D-SMES) in Wisconsin.

Recently, power utilities have also begun to use superconductor-based transformers and “fault limiters”. The Swiss-Swedish company ABB was the first to connect a superconducting transformer to a utility power network in March of 1997. Fault limiters respond in just thousandths of a second to limit tens of thousands of amperes of current. Both the US and Japan have plans to replace underground copper power cables with superconducting cable-in-conduit cooled with liquid nitrogen. By doing this, more current can be routed through existing cable tunnels. In one instance 250 pounds of superconducting wire replaced 18,000 pounds of vintage copper wire, making it over 7000% more space-efficient.

An ideal application for superconductors is to employ them in the transmission of commercial power to cities. However, due to the high cost and impracticality of cooling miles of superconducting wire to cryogenic temperatures, this has only happened with short “test runs”. In May of 2001 some 150,000 residents of Copenhagen, Denmark, began receiving their electricity through HTS (high-temperature superconducting) material. That cable was only 30 meters long, but proved adequate for testing purposes.

There are many more areas of research and application under development in superconductivity. It is an exciting field rich in potential. Several Nobel Prizes have been awarded for work related to the field.

  • 1913 Heike Kamerlingh Onnes on Matter at low temperature
  • 1972 John Bardeen, Leon N. Cooper, J. Robert Schrieffer on Theory of superconductivity
  • 1973 Leo Esaki, Ivar Giaever, Brian D. Josephson on Tunneling
  • 1987 Georg Bednorz, Alex K. Müller on High-temperature superconductivity
  • 2003 Alexei A. Abrikosov, Vitaly L. Ginzburg, Anthony J. Leggett on Pioneering contributions to the theory of superconductors and superfluids
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