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Superconducting Motor Works, but Not at Much

February 07, 1988|LARRY DOYLE | United Press International

CHICAGO — It's not a high-speed floating train, but at least it works.

Spinning at 50 revolutions per minute and not at all practical, this little motor would appear to be no more than a grade school science project--except for one thing: It runs on superconductors.

Specifically, it uses those inexpensively cooled ceramic compounds that carry electricity like greased lightning--new materials, we are told, that will save billions of dollars in energy costs and change our lives.

That makes this motor a first. But researchers at Argonne National Laboratory, southwest of Chicago, are trying not to make too big a deal out of it.

'Meant to Be a Demonstration'

"This was not meant to be a research tool, or any big advance; it was just meant to be a demonstration," said Roger Poeppel, who runs Argonne's ceramics lab. "We've always said we knew we could make a motor, but some people said, 'No, you can't. Prove it!'--and so we did."

Although inexpensive superconductors promise a tantalizing future--including sleek trains that will fly six inches above magnetized rails--their practical application has been severely limited until now. Limited, in fact, to nothing.

At Argonne, where researchers had earlier developed the first superconducting ceramic wire, Poeppel and his colleagues decided to design a motor to show off the advances they had made in materials processing. So they set out to design a special kind of engine: one that required superconductors to work.

The design they settled on is similar in many ways to standard electromagnetic motors--the grade school kind--in which electromagnets are alternately turned on and off to repel each other around an axis.

In this case, however, one of the magnets is replaced by a piece of superconductor. Although superconductors are not themselves magnets--unless coiled as such--they repel magnetic fields. This property, called the Meissner effect, is a property researchers use when they test new materials to determine whether they are true superconductors.

"It's the same repulsion you feel when you push north poles of two magnets together, Poeppel said. "They want to fly apart."

In Argonne's "Meissner Motor," 24 small electromagnets are mounted along the bottom outer edge of an 8.5-inch aluminum plate, which rotates above two hockey puck-shaped disks made of the yttrium-barium-copper superconductors.

The superconductors are activated when liquid nitrogen is added to cool them to less than 290 degrees below zero Fahrenheit and the motor starts up.

'These Motors Are Possible'

"It's too small for practical use and produces negligible power, but it demonstrates for the first time that these motors are possible," Poeppel said. "And while we didn't really learn anything from making the motor, we certainly did learn things from making the superconductors that went in the motor."

The Meissner motor is also the first time the new superconductors "have done something," Poeppel said, "something people can see."

On the other test materials, Poeppel said, "We've gotten them to conduct electricity, and I can tell you we are measuring current, but it still just sits there."

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