Absolute Zero and the Conquest of Cold (32 page)

In professional conferences with such titles as "Inner Space/Outer Space," physicists explored the efforts to record the big-bang relic particles of deep space and the efforts being made to understand subatomic particles in earthbound laboratories. Since World War II, physicists had relied for investigation of subatomic particles on accelerators, synchrotrons, and eventually, colliders that raised the particles' speed to near the velocity of light. The objective was to let the particles smash into obstacles or into each other, so they would disintegrate into interesting pieces.

One way to make faster accelerators was to use more magnetic power to accelerate the beams. Superconducting wires seemed to be the answer. Although it was known that the application of a magnetic field to most superconducting materials could make those materials lose their superconductivity, there were other superconducting materials that could successfully be made into wires and coils, wrapped around themselves—with no metallic core—to provide higher magnetic force. Such superconducting magnets were used to increase the sensitivity and effectiveness of magnetic resonance imaging (MRI) devices, employed in medicine to detect diseases such as cancer in soft tissues that x-rays could not reveal. They also became critical components in masers, microwave precursors of lasers that were used for communications and are still used to detect remote astronomical events. In high-energy physics, superconducting magnets were incorporated into the design of new accelerators, to raise the speed of the beams of subatomic particles being hurled at one another. Important discoveries about subatomic particles were made with these new accelerators, such as the Tevatron at the Fermi National Accelerator Laboratory in Illinois.
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Superconducting magnet colliders showed such promise that governments in the United States and in Europe agreed to build multibillion-dollar "superconducting supercolliders" (SSCs); one expert calculated that to raise particles to the same energy level as the American SSC would make possible, an accelerator constructed in the same way as the 2-mile-long one at Stanford University would need to be 100,000 light-years long.

Just after completion of the first several miles of the 54-mile tunnel near Waxahachie, Texas, that would hold the American SSC, and a test of the first of the six accelerator stages in which hydrogen ions were successfully smashed, in the early 1990s congressional budget cutters shut down the SSC, arguing that $2 billion had already been spent with little to show for it. Following the cancellation of the SSC, several hundred scientists and engineers left the United States to join the European project; with this shift, the center of research on particle physics relocated to near Geneva, site of the Large Hadron Collider.

In 1975 physicists suggested a new way to study atoms, not by accelerating them but by simultaneously slowing and cooling them. In 1985 Steven Chu of Bell Labs ingeniously used lasers fired from six directions to make what he called an "optical molasses," a "trap" to intercept and slow incoming atoms to speeds measured in inches per second. The trap confined a few thousand atoms to one spot, at a temperature of 240-millionths of a degree above absolute zero. Chu's concept was extended by an even better magnetic-trapping device perfected in the following years by William D. Phillips of the U.S. National Institute of Standards and Technology, then explained theoretically by Phillips, Chu, and Claude Cohen-Tannoudji of the École Normale Supérieure in Paris, who cooled the atoms even further, to within one-millionth of a degree above absolute zero. Chu, Phillips, and Cohen-Tannoudji were awarded the 1997 Nobel Prize for their achievement.

While this exciting development was invigorating research into subatomic particles, an astonishing advance was made in the field of superconductivity. Since the time of Onnes, scientists had been trying to find materials that became superconductive at temperatures higher than that of liquid helium, believing that only when superconductivity could be produced easily and economically could it be put to the tremendous practical uses Onnes and every subsequent thinker in the field had envisioned—free-flowing electric currents, more powerful magnets, a world with a near-infinite capacity to conserve and distribute its energy supply. Onnes had discovered superconductivity in mercury at 4.19 K; in the ensuing seventy years, the record for the "critical temperature" at which superconductivity commenced had been raised only 19 degrees, to 23.2 K for a compound of niobium, a rare metal. At IBM's Zurich laboratory, in the early 1980s Karl Alex Müller and his junior associate Johann Georg Bednorz began working with metallic oxides to see if they could be made superconductive; oxides—combinations of oxygen with other elements—were a bit of an odd choice, since some were used as insulators, and many had no electrical conductivity at all, although a few had been shown capable of becoming superconductors. Working more like chemists than physicists, Bednorz and Müller mixed compounds, baked the mixtures in ovens, and then chilled them to liquid-hydrogen temperatures. They did their work without lab assistants, and without much encouragement from their colleagues in the laboratory; Bednorz even had to steal time from his regular assignments to perform the oxide experiments. After two and a half years of trying various compounds, on January 27,1986, they succeeded in making an oxide of barium, lathanum, copper, and oxygen that became superconducting at 35 K. Being cautious, telling almost no one of their accomplishment, they prepared an article in April for publication in September 1986 in
Zeitschrift fur Physik.

An explosion of research and excitement followed that publication, as laboratories in Japan, China, England, Switzerland, and the United States jumped into the chase for a compound that would become superconducting above 77 K, the temperature at which nitrogen liquefied. Since the liquefaction of nitrogen had become routine and inexpensive, if liquid nitrogen could be used to produce superconductivity, scientists reasoned, there ought to be no limit to employing superconductivity for the profit of whatever entity could patent the compound having the highest "critical temperature." A frantic six-month scramble among the laboratories led to the jam-packed "Woodstock of Physics" meeting in New York City on March 18,1987, at which the major groups reported their recent research—some accomplishments so new that the ink was not yet dry on articles about them. The winner of the chase for the compound that was the easiest to create, and that had the highest critical tempera
ture, was Paul Chu's laboratory at the University of Houston, whose "1-2-3" compound became superconductive at an astounding 93 K.

A media frenzy followed, reaching and involving the uppermost levels of governments on several continents, as superconductivity achieved at liquid-nitrogen temperatures (above 77 K) was touted as the key to everything from Star Wars missile defense systems to superfast computers to energy storage and transmission devices that would drastically lower the price of electric power. In the delirium over what seemed the ultimate use of the extreme cold, an eighth-grade science teacher—the daughter of an IBM physicist—used the "Shake 'n Bake" method to cook a wafer of the new compound in a regular oven, then placed it in a dish of liquid nitrogen and magically floated above the dish a tiny magnet. Cornelis Drebbel would have been pleased.

Müller and Bednorz were awarded the 1987 Nobel Prize in physics, and there were high hopes that the 1990s would be the decade in which "high-temperature superconductivity" (HTS) would revolutionize the world. When these overblown expectations were disappointed by the difficulty of fashioning the new compounds into electrically conductive wires, and of constructing ways to maintain them at liquid-nitrogen temperatures, it seemed as though a balloon had burst. However, sure and steady progress in utilization was made in the decade after the 1987 Woodstock of Physics—an industry journal claimed that the "pace of utilization" of HTS was on a par with that achieved by other high-tech "overnight sensations" such as microprocessor chips. More than one hundred new HTS compounds have been created, with onset temperatures as high as 134 K, nearly twice as warm as liquid nitrogen.

Equally important, the practical use of superconducting wires has begun. In Geneva, the public utility now has a transformer wound with HTS-compound superconducting wires to step down the voltage from the country's power grid; since the new transformer runs without oil, the likelihood of the fires and pollution that often
occur with regular transformers is drastically decreased. In Detroit, a contract has been awarded to the American Superconductor Corporation to produce a 400-foot-long superconducting line for that city's public utility by the year 2000; the line's 250 pounds of superconducting wire will carry as much current as 18,000 pounds of the existing copper wire. Among the costs saved are significant environmental ones, since the creation of 250 pounds of superconducting wire uses up considerably fewer natural resources than does the extraction, refining, and manufacture of 18,000 pounds of copper wire.

In North Carolina, the public utility offers superconducting magnetic-storage devices to commercial customers for use in countering unexpected power surges and dips. Other projects nationally include a superconducting generator coil, a 125-horsepower motor, many times smaller than usual motors, and improved SMES (superconducting magnetic energy storage) systems, in which the magnets are charged during off-peak hours when demand is low, enabling them to make more power available to the grid when demand rises. The U.S. Department of Energy estimates that if all public utilities switched to superconducting transmission and distribution lines, they would be 50 percent more efficient. Expected for the future is a shift from generating plants in and near cities to ones in remote locations, or ones that use less expensive solar or geothermal energy sources to produce electric power, which can then be cheaply and efficiently transmitted for use in population centers. An added bonus expected from these sources is that more efficient transmission of power will diminish pollution.

The new HTS superconductors show equal promise for electronic equipment: they are being used to filter signals from noise in cellular-phone base stations, improving cell-phone reception; they are reducing imaging time, improving resolution, and lowering the costs of MRIs. Perhaps the most unexpected use is in sewer and water-purification systems: iron compounds are salted into the liquids, where they bond with undesirable bacteria and viruses, form
ing substances that superconducting magnets can then attract and remove. A similar "magnetic separation" process is being used in portable devices to clear contaminated soil sites, including sites that contain the radioactive compounds called actinides. Other high-tech applications are on the drawing board. Superconductivity applications seem likely to become the sixth major industry based on mastery of the cold.

In terms of numbers of people and industries served the technologies of cold are at an all-time high. Virtually all American homes have refrigerators, and most have air conditioners, as do all modern business buildings from factories to warehouses to corporate headquarters. In the Far East, the major source of energy for electric power is rapidly becoming LNG. Oxygen transported in liquefied form is in use in all hospitals. Other liquefied gases are critical to dozens of manufacturing processes; worldwide, annual sales of such gases total $10 billion, with the American-based company Praxair accounting for about half of that. Throughout the industrialized countries, most people daily use electronic devices made with, food preserved by, or chemicals manufactured by means of liquefied gases and the cold they produce. Increasingly, what separates the "have" from the "have-not" nations of the world is that the first group makes more use of the cold.

Still more uses are coming. In 1998 two milestones were reached in the use of superconducting magnets. In one, the first 18.4 kilometers (11.4 miles) of track for Japan's "maglev"—magnetic levitation—train was opened. The sets of magnets in the train, the tracks, and the ancillary equipment float the train millimeters above the guide track and serve to accelerate it along the track at speeds much faster than can be achieved by any system in which the train and track are in contact. In the second milestone, superconducting magnets were employed in brain surgery; in St. Louis, in December 1998, the magnets were used to direct a surgical instrument around corners and on a curved path through the brain, avoiding vital sections, to perform a tumor biopsy. The process was considerably less invasive than conventional methods and is expected to be used in the near future to treat motor disorders such as Parkinson's disease that are centered in the brain, as well as to treat cancer and heart disease in other areas of the body.

The new Kamerlingh Onnes Laboratory at Leiden opened in late 1998, and while it, too, works with HTS materials, its main mandate is to explore many frontiers of physics at temperatures capable of being generated by liquid helium. At one end of the research "factory," an automated production facility manufactures large quantities of liquid helium, which is then held in 5,000-liter containers and siphoned off into smaller ones. A screen saver on the computer in the production facility asks, as Onnes might have done, "How much helium have you wasted today?" Containers of the precious fluid are wheeled down corridors to the other end of the building, where a dozen cryostats and associated measuring equipment are located on concrete-and-steel platforms specially constructed to eliminate all vibrations.

Scientists working at the cutting edge of physics increasingly choose to investigate all sorts of physical phenomena by means of low temperatures, says the Leiden lab's current director, Jos de Jongh, because at micro- and millikelvin temperatures "you can eliminate all the extraneous influences," such as radiation and vibration, and be more certain that the only variable is the phenomenon under study. For instance, de Jongh, his graduate students, and visiting researchers from several countries recently completed studies of how large a metallic cluster must be before it stops behaving like a collection of atoms and starts behaving like a bulk object; the answer was in the range of 150 atoms. Other studies in the lab have used special cameras operating at ultra-low temperatures to observe the crystallization of helium-3 at millikelvin levels.