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New research is unlocking the amazing potential of high-temperature superconductors.

by Patrick L. Barry

Few technologies ever enjoy the sort of rock-star celebrity that superconductors received in the late 1980s.

Headlines the world over trumpeted the discovery of "high temperature" superconductors (abbreviated HTS), and the media and scientists alike gushed over the marvels that we could soon expect from this promising young technology. Levitating 300-mph trains, ultra-fast computers, and cheaper, cleaner electricity were to be just the beginning of its long and illustrious career.

Today we might ask, like a Hollywood gossip columnist: what ever happened to the "high-temp" hype?

"It was the hottest potato of its time, but it all fizzled out," says Louis Castellani, president of the Houston-based HTS company Metal Oxide Technologies, Inc. (MetOx).

The problem was learning to make wire out of it. These superconductors are made of ceramics - the same kind of material in coffee mugs. Ceramics are hard and brittle. Finding an industrial way to make long, flexible wires out of them was going to be difficult.

Indeed, the first attempts were disappointing. So-called "first generation" HTS wire was relatively expensive: 5 to 10 times the cost of copper wire. Furthermore, the amount of current it could carry often fell far short of its potential: only 2 or 3 times that of copper, versus a potential of more than 100 times.

Image courtesy MetOx

"Second generation" HTS wire can carry the same amount of current as copper wire hundreds of times as thick.

But now, thanks to years of research involving experiments flown on the space shuttle, this is about to change.

The NASA-funded Texas Centre for Superconductivity and Advanced Materials (TcSAM) at the University of Houston is teaming with MetOx to produce the "smash hit" that scientists have been seeking since the '80s: a "second generation" HTS wire that realizes the full 100-fold improvement in current capacity over copper yet costs about the same as copper to produce.

Once-famous superconductors may be about to step back into the limelight.

The audience awaits

The special "talent" of superconductors is that they have zero resistance to electric current. Absolutely none. In theory, a loop of HTS wire could carry a circling current forever without even needing a power source to keep it going.

In normal conductors, such as copper wire, the atoms of the wire impede the free flow of electrons, sapping the current's energy and squandering it as heat.

Today, about 6 to 7% of the electricity generated in the United States gets lost along the way to consumers, partly due to the resistance of transmission lines, according to U.S. Energy Information Agency documents. Replacing these lines with superconducting wire would boost utilities' efficiencies, and would go a long way toward curbing the nation's greenhouse gas emissions.

MRI scans, a powerful tool for medical diagnosis, use superconducting electromagnets to generate detailed images of body tissues. Most of today's MRI machines require expensive liquid helium to cool their low-temperature superconducting wire.

The fledgling "maglev" train industry would also welcome the availability of higher-quality, cheaper HTS wire. Economic realities stalled the initial adoption of maglev transit systems, but maglev development is still strong in Japan, China, Germany, and the United States.

NASA is looking at how superconductors could be used for space. For example, the gyros that keep satellites oriented could use frictionless bearings made from superconducting magnets, improving the satellites' precision. Also, the electric motors aboard spacecraft could be a mere 1/4 to 1/6 the size of non-superconducting motors, saving precious volume and weight in the spacecraft's design.

Should we ever establish a base on the moon, superconductors would be a natural choice for ultra-efficient power generation and transmission, since ambient temperatures plummet to 100 K (-173 C, -280 F) during the long lunar night - just the right temperature for HTS to operate. And during the months-long journey to Mars, a "table top" MRI machine made possible by HTS wire would be a powerful diagnosis tool to help ensure the health of the crew.

Worldwide, the current market for HTS wire is estimated to be US$30 billion, according to Castellani, and it is expected to grow rapidly.

A backstage pass

The University of Houston has licensed this new wire-making technology to MetOx, a company founded in 1997. MetOx plans to begin full-scale production of this high-quality HTS wire in 2003, Castellani says.

Not surprisingly, the primary scientist for the NASA group at TcSAM, Dr. Alex Ignatiev, can't reveal exactly how they make their HTS wire. The technologies springing from these NASA/industry research partnerships must be patented to achieve NASA's goal of using space to benefit American businesses, Ignatiev says.

Image courtesy NASA

The Wake Shield Facility being held out in space by the shuttle's robot arm.

He will, however, share the dinner-napkin sketch.

Basically, the wire is made by growing a thin film of the superconductor only a few microns thick (thousandths of a millimetre) onto a flexible foundation. This well-known production method was improved upon in part through "Wake Shield" experiments flown on the space shuttle to learn about growing thin films in the hard vacuum of space.

"We learned how to grow higher-quality oxide thin films from the shuttle experiments, and used that in the lab to improve the quality of our superconducting films," Ignatiev says.

In the years to come, that quality will translate into improvements in dozens of industries from power generation to medical care. Keep an eye on this one: the glamorous career of superconductors has only just begun.


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First Science 2014