Deep-Freeze For Electricity

Press, Volume CIII, Issue 30478, 27 June 1964, Page 14

Deep-Freeze For Electricity

Electric power may in the future be carried long distances on refrigerated lines, maintained at or below 4deg Absolute (-269 deg Centigrade), the temperature at which helium liquifies, Dr. N. Kurti, reader in physics at the University of Oxford, said yesterday.

The wires would be made of materials which are “superconductive”—that is, which have virtually no electrical resistance—at very low temperatures.

“The possibility is being actively looked into, and pilot-scale experiments are being carried out,” Dr. Kurti said. Superconductivity could be useful in transformers as well as in’ transmission lines.

“If anyone had suggested 15 years ago that this might ever be possible on a large scale, he Would probably have been certified,” he said.

“But it was discovered in America, by workers at the Beil Telephone Laboratories, that certain materials such

as alloys of niobium and zirconium retain superconductive properties even at high current densities, and this fact, combined with the new availability of efficient and relatively cheap ‘superrefrigerators,’ makes such a scheme feasible."

By proper construction, such as the provision of several layers of heat-insulation, it could be ensured that the take-up of heat was not too large. Dr. Kurtl said. The system could be maintained by modest-sized automatic super-refrigerators every few miles.

Another practical use for low-temperature engineering. Dr. Kurti said, was in rocket propulsion. One of the most important rocket fuels, especially for inter-planetary travel, was liquid hydrogen. Degrees Absolute are measured from. the—unattainable —absolute zero, which is equal to' -273 deg. Centrigrade. A degree on the Absolute scale is equivalent to a degree on the Centigrade scale. The temperatures reached in Oxford University’s Cavendish Laboratory, where Dr. Kurti works, are very much lower than the boiling-point of helium—about four million

times lower, in fact A new technique, using the magnetic moment of atomic nuclei, has enabled temperatures to be reached in the region of one-millionth of a degree Absolute. Dr. Kurti thinks refinements in this technique will enable the limits to be pushed down to one hundredmillionth or even one thou-sand-millionth of a degree Absolute.

“I can’t think of any other sub-atomic particles we could work on to enable us to reach temperatures lower than this, so it could be that, the range one hundred-million to one thousand-millionth of a degree is the lowest at which it is possible—or interesting—to work,” Dr. Kurti said. When a material was to be cooled from room temperature down to these very low levels, a "cascade system” was used, Dr. Kurti explained in his laboratory, liquid air was first used, then liquid hydrogen, then liquid helium. This could bring the temperature down to about one degree Absolute. From there, a magnetic cooling method was used, relying on the property of certain substances (mainly paramagnetic salts) to warm up when put in a magnetic field; this method, using the

magnetic moment associated with electrons, could take the temperature down to onethousandth of a degree Absolute. The new nuclear magnetic moment technique, involving the alignment of the nuclear magnets, was then used.

The newly-attained very low temperatures were being used in a search for further super-conducting materials, said Dr. Kurti. It was particularly interesting, he said, to see whether metals which showed no sign of superconductivity at levels previously reached might become superconductive when cooled still lower. Other physical characteristics, such as specific heats and electrical resistivity, were being examined.

Dr. Kurti, a Hungarian by birth, has been at the Clarendon Laboratory since 1933. He is visiting New Zealand under the auspices of the British Council, on his way home from a year spent as a visiting professor in the United States, first at City College, New York, then at the Berkeley University of California. Yesterday he addressed students and lectured in the physics department and engineering school of the University of Canterbury.