Motoring in liquid nitrogen.

Motoring in liquid nitrogen 

It hasn't taken researchers very long to put high-temperature superconductors to work. Recently, technicians at the Argonne (Ill.) National Laboratory used one of the new materials to construct a simple, electrical motor based on the property that superconductors repel magnets -- a phenomenon known as the Meissner effect.

The Meissner motor consists of a circular aluminium plate, 8.5 inches in diameter, with 24 small electromagnets mounted along the bottom of its outer edge. The plate rotates above two disks composed of yttrium-barium-copper oxide, a superconducting ceramic. Because this material becomes superconducting at the relatively high temperature of 94 kelvins, or -- 290 [deg.] F, liquid nitrogen is cold enough to keep the disks at an appropriate temperature. Repulsion between the electromagnets and the superconducting disks causes the plate to spin at a rate of 50 revolutions per minute.

"It's too small for practical use and produces negligible power," says Argonne's Roger Poeppel, "but it demonstrates . . . that thase motors are possible."

Meanwhile, researchers at Cornell University in Ithaca, N.Y., have developed a superconducting motor that spins at up to 60,000 rotations per minute. Developed by Francis C. Moon and Rishi Raj, the motor has a magnetically levitated rotor weighing about 10 grams nestled in a superconducting bearing specially designed to provide stable levitation forces. The use of superconducting materials simplifies the design of magnetically levitated, high-speed rotors, which, when fabricated from conventional materials, require special feedback circuits and operation in a vacuum. The new motor may turn out to be useful for gyroscopes and in robotic applications.