Conductors Take 'Super' Strides
Scientists are developing superconducting ceramic wire, coils that offer greater efficiency
WHEN technicians at the International Superconductivity Technology Center in Toyko levitated their director, Shoji Tanaka, last fall, it was not just another stunt to hype the wonders of loss-free electric currents.He stood on a magnet floating above a superconducting plate. The ability to make that plate illustrated the unexpected progress that, a year later, continues to encourage scientists in this difficult research field. News reports put a bloom of false promise on the discovery of the new superconducting materials in the mid-1980s. These ceramic substances lose electrical resistance at far higher temperatures than previously known superconductors. Engineers can cool them with liquid nitrogen at 77 degrees kelvin (minus 321 F) or perhaps even with low-temperature refrigerators. This is cheaper and simpler than the liquid helium cooling at 4.2 degrees kelvin (minus 452 F) that the old superconductors need. The reports prophesied magnetically levitated trains, loss-free transmission of electricity, frictionless motors, and superfast computers. Realism set in when researchers explained that they didn't know how to fabricate the brittle ceramics into useful devices. In fact, they didn't know - and still don't know - how the superconducting ceramics work. Thus the false promise yielded to what has turned out to be equally misleading pessimism. "The news is that, 18 months ago, people didn't think they would have made the progress they have made today," says Alan M. Wolsky at Argonne National Laboratory near Chicago. Working under a three-year 13-nation agreement, Dr. Wolsky heads a worldwide study of high-temperature superconductivity research and its impact on the electric-power industry. He explains that learning to make superconducting wire from materials that have more in common with brick than ductile metals is the key development. It is here that he sees "solid progress has been made." Laboratory processes now produce superconducting wire up to several meters in length. Wolsky sees no fundamental obstacle to developing commercial-grade wire many meters long. However, he cautiously adds, "I can't predict what will happen in the future." John Rowell, president of Conductus Inc. in Sunnyvale, Calif., is equally encouraged by developments in the electronics field. He was guest editor for a special issue on high-temperature superconductors published last June by the American Institute of Physics journal Physics Today. Looking at the field from that perspective, he says he finds "surprising progress." He explains: "Three years ago, we were all standing around wondering what [superconducting electronic] devices we would have to work with. Now we have a whole spectrum of devices." Like Wolsky, Dr. Rowell finds it hard to foresee what practical applications these basic circuits will have. Yet he says that some applications, such as bolometers to measure heat radiation or sensitive magnetic field detectors, seem close at hand. He explains that engineers need no technical breakthroughs to design these instruments. The challenge is learning to make them cheaply and reliably on a factory production line - a challenge his company, among others, now is pursuing. Engineers like superconductors for several reasons. They make possible more efficient and more compact electronic components. Carrying electric currents with little loss could bring new efficiency to power transmission. It also brings new efficiency to electromagnets. The resistance in the copper coils of a conventional, high-field (10 tesla) magnet dissipates so much electrical energy that cooling water must remove heat at a rate equal to the power needed by a small city. A superconducting coil can generate the strong magnetic field without degrading electric power into heat. That is why designers of high-energy particle accelerators use superconducting magnets based on the old helium-cooled technology. Magnets using the new high-temperature superconductors could lead to simpler, cheaper designs. Wolsky points out that small magnets using the new materials could also find a large market in research laboratories. He explains that, first, they would operate at the old liquid-helium temperature. Their advantage would lie in producing stronger magnetic fields than is possible with the old superconductors. Then, as engineers learned to make magnets operate in the higher, liquid-nitrogen temperature range, the resulting strong, compact magnets would make much present lab equipment obsolete. Superconductors also have the useful property of expelling magnetic flux. A magnet dropped onto a superconductor will float above it, as did Mr. Tanaka's levitated platform, which showed that scientists are learning how to handle the new materials in bulk. PHYSICIST Miles Klein, director of the superconductivity center at the University of Illinois at Urbana- Champaign, says bulk handling - using the superconducting ceramics in relatively large pieces - is another research area "where there has been substantial progress." Magnetic levitation is a promising specialized area. Reviewing this last March in Nature, aerospace engineer Francis C. Moon of Cornell University in Ithaca, N.Y., explained: "Given the potential for high-speed, contactless, no-wear, stable levitation of small and large rotors, superconducting magnetic bearings may become the first 'sleeper' application of the high-temperature [superconductor] revolution." The ad hoc Industry Working Group on Power Applications of High-Temperature Superconductors (HTSC) made a similar point in its report last April. The group includes researchers from academic, industrial, and national laboratories. It noted that motors consume "about 65 percent of all electrical energy" in the United States. Therefore, it added, "development of HTSC motors could yield substantial energy savings." Given the unexpected progress in handling the new superconductors, the group's report concluded that "serious development of HTSC applications should begin now." The US government is spending around $250 million on a range of superconductor research this year. Yet the report notes that relatively little of this effort is relevant to electric-power systems. It urges a five-year, $250-million, government-led "banner program" to develop practical HTSC power-system technology. That includes friction-free motors, magnets, and wires and other high-current carrying devices. Were such a program adopted, it, like other aspects of the new superconducting technology, would have to go ahead with little guidance from basic physics. The theorists simply do not know what is going on. This is a field where "craft has gone ahead of theory," Wolsky says. Rowell agrees. But he isn't much concerned about the lack of theory. He says that "feeling our way" is the way to go. He adds that "the work is moving well toward practical devices even in the absence of theory." Nevertheless, physicist Klein calls the physics of the new materials "a first-class problem." He explains that it probably is part of a larger problem in understanding the solid-state physics underlying the properties of materials. "As a purely intellectual endeavor, this is very exciting," he says. "It could have a big theoretical payoff."