"Maglev Goes to Work," Feature Article, June 2006

maglev goes to work

A mixer taking advantage of high-temperature superconductors enters the pharmaceutical market.

by Alan S. Brown, Associate Editor

ever since the discovery of high-temperature superconductors in 1986, magnetic levitation has been their poster child. Pictures of frosted superconducting ceramics suspended in mid-air have appeared in countless magazines, newspapers, and Web sites. Companies sold magnetic levitation kits to schools and researchers. Artists drew beguiling renderings of maglev trains.

It has taken nearly 20 years for the first maglev device using high-temperature superconductors to reach the market. It is neither a train nor any other application originally envisioned when high-temperature superconductors first burst upon the scene. Although Central Japan Railway Co. a few months ago tested the first-ever maglev train using high-temperature superconductors, that technology is still a long way from practical commercialization.

Instead, LevTech Inc., a Lexington, Ky., startup is using yttrium-barium-copper oxide superconductors to suspend impellers in mixers and pumps for the bioprocessing and pharmaceutical industry.

Locked in Place

Both mixers and trains take advantage of the ability of superconductors to expel nearby magnetic fields from their body. This repulsion is what enables a superconductor to hold a conventional magnet—or a maglev train—aloft.

Trains also can take advantage of the ability of superconducting magnets to attract the opposite pole of another magnet at a distance. Mixers, however, take advantage of a less well-known phenomenon, the ability of superconductors to lock nearby magnets into place.

This property is visible in pictures of levitated superconductors. If all the superconductor did were to repulse a nearby magnet, it would eventually push the magnet out of its magnetic field until it fell on the table.

Instead, superconductors will lock onto a magnet as long as the flux from that magnet penetrates the superconductor before it cools down to superconducting temperatures. Rather than expelling this magnetic field from its body, it actually pins the magnet's lines of force, fixing the magnet in place even as it pushes it away.

LevTech's mixer, invented by company founder and former University of Kentucky physicist Alexandre Terentiev, uses this principle to both suspend and lock other magnets into place. Its design is at once both simple and ingenious.

The Central Japan Railway's magnetic levitation railroad, still in the test stage, is the world's only one to use superconductive magnets like the one shown below. The first commercial use of maglev, using high-temperature superconductors, will be completely different.

Terentiev started with six high-temperature superconductors, each about as large as a quarter and twice as thick. He arranged them in a circle inside a 3-inch-diameter cassette. He then molded permanent magnets into his polyethylene impellers. As he chills the superconductors to their 68 kelvin operating temperature, they lock onto the impeller magnets and lift the entire structure aloft.

Turning the impeller is quite simple. Terentiev merely switches on a motor and the cassette holding the six superconductors begins to rotate. This drags the suspended impeller with it. According to Levtech chairman Jeff Craig, the mixer is effective at viscosities up to 800 centipoise, roughly equivalent to cold maple syrup.

The design is a natural for biopharma processing, he said. "A typical bioprocess, especially one that involves a recombinant protein, involves 15 to 20 steps where sterile mixing is desired," Craig said. In the past, the industry did all that mixing in conventional stainless steel tanks, which require extensive sterilization after each operation.

More recently, the industry has been switching to pre- sterilized plastic bags, which it can dispose of after use. This minimizes capital costs, cleaning time, and wastewater treatment. The industry, however, has struggled to find ways to mix its products in disposable bags. The most common method today is to put a bag on a rocker table and slosh the liquid around inside.

"We can spin the magnetic impeller inside a vessel without any shafts, bearings, or seals," Craig said. "It's 100 percent clean. There's no friction, no shedding of particles, no generation of heat, no maintenance of expensive bearings, and no risk of contamination." According to Craig, the drive unit can mix bags up to 1,000 liters, and the company is developing one that can handle 2,000-liter bags.

LevTech has over 40 superconducting mixers in the field, with more to come following a distribution deal with German bioprocessing leader Sartorius AG. It's working on a pump that will also use external superconductors to drive its impeller. While the technology is likely to find early use in biopharma production, Craig sees possible uses in cosmetics, personal care products, food processing, fine chemicals, and mixing of semiconductor processing chemicals.

Railroading at 20 K

Meanwhile, the development with trains took place late last year. Between November 22 and December 9, Central Japan Railway Co. tested the first-ever maglev train using high-temperature superconductors. The train reached a top speed of 310 miles per hour on JR Central's Yamanashi maglev test line, a 27-mile-long track that runs between Sakaigawa and Akiyama south of Tokyo.

JR Central has been testing maglev trains based on conventional low-temperature superconductors at Yamanashi since 1997. The trains have carried more than 100,000 passengers on test rides for a total of 290,000 miles. Ultimately, the railroad hopes to build a maglev line that could noiselessly whisk 10,000 passengers per hour over the 300 miles between Tokyo and Osaka.

Superconductors aren't the only maglev game in town. Several companies, led by Germany's Transrapid International GmbH & Co., have developed maglev systems based on conventional electromagnets. A maglev shuttle operated in Birmingham, England, for 11 years until it closed in 1997. In 2004, Transrapid completed an 18-mile maglev line that now serves Pudong International Airport from Shanghai, China.

According to JR Central, superconductors have certain advantages over conventional electromagnets. First, they are much lighter. This improves railcar acceleration, speed, and payload. They also use less energy. More importantly, though, their 1 Tesla magnetic fields can lift a train 3 to 4 inches off the track, compared to 0.3 to 0.4 inch achieved with ordinary electromagnets. The wider air gap separates the vehicle from branches or pebbles on the track and from track movements due to earthquakes (always a possibility in Japan). It yields a smooth ride at near-airline speeds.

The LevTech mixer's cassette holds six superconducting magnets, which suspend and lock into place an impeller that can be isolated in a presterilized mixing bag. Rotating the cassette turns the impeller, which stirs the biochemicals inside the sealed bag.

The downside of superconductors has been their expense. Superconducting wire is far more costly than copper wire used for electromagnets and requires complicated cooling to reach operating temperatures. JR Central had to cool its low-temperature niobium titanium alloy superconductors to 4 K
(-269°C) using liquid helium and liquid nitrogen before they became fully superconductive.

High-temperature superconductors reach maglev operating temperatures at 20 K (-253°C). The 16° difference may not sound like much, but it allowed engineers to cool the magnets directly with a freezer. This eliminated costly liquid helium devices and improved system reliability.

Unfortunately, these first-generation high-temperature superconductors are not economical enough to justify a Tokyo-Osaka maglev rail line. Help is on the way, however, in the form of improved superconductor wires, according to Greg Yurek, chief executive officer of American Superconductor Inc. of Westborough, Mass.

Yurek's company, which provided JR Central with the high-temperature superconductors for its recent tests, is currently working on second-generation wires. Yurek promises that they will cost two to five times less than first-generation wires and turn superconductive at a relatively balmy 55 K (-218° C). According to JR Central, switching to second-generation wires would reduce the cost of the Tokyo-Osaka line by roughly $840 million.

Will that make the Tokyo-Osaka maglev line economically viable? JR Central's maglev research is a Japanese national project. The company says the project is not yet finished, so it does not yet know if it will ever build the line.

Yurek is more sanguine. "I'm impressed by the fact that they started working on superconducting maglev in the 1960s," he said. "They've built bridges, tunnels, switches, and guideways. After spending 50 years developing this transportation system, I think they're probably going to carry it through."

If JR Central follows through, then LevTech's mixer may have to make room for maglev's next poster child.

How Maglev Trains Work

Central Japan Railway's magnetic levitation system does more than just suspend trains above a guideway, or track. It also propels them forward while keeping them centered on the guideway. Here's how it works:

Levitation. Powerful superconducting magnets located on the railcars control levitation and centering. As the superconductors in the train speed past the figure-eight levitation coils attached to the sides of the guideway, they induce an electric current in the coils. This turns the coils into electromagnets. The poles on the coils simultaneously push and pull the superconducting magnets upward, suspending the train over the track.

Guidance. The levitation coils are also connected under the guideway to form a loop. As the superconducting magnets move past this loop, they induce an electric current in the coils. The coils nearest the train repulse the superconducting magnets aboard the train, while those coils further attract them. As the train moves toward the center, the magnetic forces grow proportionately weaker and stronger, thus keeping the train centered.

Propulsion. Electromagnetic coils embedded in the guideway walls govern propulsion. These coils switch alternately between north and south poles, alternately pulling and pushing the train and its superconductors forward.