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LAKE WALES Fla.—Room-temperature superconductors are getting closer-and-closer now that separate research groups in the U.S. and Europe have improved a theory, namely that "critical states" at not fixed temperatures backed up by experimental results—and the highest temperature superconductor yet has been proven to be depend on quantum effects that open the possibility of optimizing compounds for room-temperature operation.

"The 'critical state model' has had continued success since circa 1963. One of its rock-solid predictions is that in order to magnetize a piece of bulk superconducting material to its maximum obtainable field, one must apply a field exceeding 2X that maximum," professor Roy Weinstein told EE Times. "The actual factor is almost always larger than 2, and depends upon the geometry of the bulk. Most typically, for bulks used in applications, the factor is 3.2X. The magnetized bulk superconductor then acts like a permanent magnet, called a "trapped field magnet" (TFM)."

In Weinstein's experiments, however, his group has shown readily applicable circumstances under which the bulk is fully activated by an applied field only equal to the permanently magnetized state (1X).

"Our experiments show many other interesting results, but these are of interest mostly to physicists rather than engineers," Weinstein told EE Times. "There are very fast increases in field penetration into the superconductors. These are greater than 100 times faster than allowed by CSM. Also the heat generated in the activation process has limited all previous activation methods, but in the newly discovered circumstances, exceptionally little heat is generated."

Weinstein's group's new formulation of superconducting theory, also has allowed them to build superconducting motors and generators which are more than 16X as powerful for the same size, or conversely could be 16-time smaller that equivalent superconducting motors and generators today.

In general, the new superconducting theory can increase magnetic fields by a factor of 3.2X. For instance, for a given torque, the rotor diameter could be reduced by 3.2X, and likewise the volume of the motor by 10.2 (3.2-times-3.2). Alternatively, for the same sized motor, the torque density could be improved by 3.2X. And in either case, the current pulse providing the activating magnetic pulse, requires 3.2 less current reduced thus reducing the power consumption by almost 10 times.

A magnet levitated over a high-temperature superconductor array using a super-small rectangle trapped field magnets (TFM, black) levitating a heavy ferromagnet (silver) above a container of liquid nitrogen.

(Source: Weinstein/University of Houston)

"In designing a motor or generator, there is some practical limit to the magnitude of pulsed magnetic field which you can build into the device to impress field into a superconductor, in order to have it behave like a permanent magnet. Just to give an example, assume that the activating pulse cannot (practically, or because of cost) exceed 12 Tesla. CSM would predict that the practical maximum to which the superconducting magnet can be activated is 3.75 Tesla (12T ÷ 3.2)," Weinstein told us. "But using our new discovery, the bulk can be activated to 12T (12T÷1.0). This is about 17 times the strength of present day ferromagnets."

The applications of TFMs—as high as 17 Tesla "boggles my mind" claims Weinstein especially since they can be activated by magnetic pulses no greater than those needed for a permanent magnet.

However, we won't see these miracle magnets, motors and generators on the shelves anytime soon, according to Weinstein who claims it will take years just to convince manufacturers to invest the huge sums necessary to switch over their operations to the new techniques. Also Weinstein's group needs to clarify the precise manufacturing steps needed and produce more prototypes to convince the doubting Thomas's of the world.

"The design rules will involve engineers and physicists working together. Then the engineers will have to work hard to optimize the designs for various applications. Only then will the public see the advantages in terms of lower power bills, faster ships, better red blood supplies and so on," Weinstein told us. "Also these applications will almost all be large devices, to mitigate the overhead cost of the need to cool the superconducting magnets to their operating temperature."

Read about the conditions under which Weinstein's group creates their amazing superconducting magnets in Anomalous results observed in magnetization of bulk high temperature superconductors—a windfall for applications in the Journal of Applied Physics>/em> (AP).

Room-temperature superconductors?

"Room-temperature superconductors are presently only a dream," according to Weinstein. "But that dream has made significant progress. The temperature at which certain materials can superconduct has been increased about 25 times since the first discoveries. It needs to be increased by another factor of about 3 to reach room temperature."

Hot on the trail of room-temperature superconductors is another group reporting this week that quantum effects in superconducting compounds containing hydrogen crucially affect the temperature at which a material becomes superconducting.

Research performed at the Universidad del País Vasco, Euskal Herriko Unibertsitatea, the Donostia International Physics Center, the Sorbonne University of Paris, and the University of Rome La Sapienza' claims to show that sulfur hydride superconductor—the highest reported temperature superconductor (at -94 Fahrenheit) is due to providing enough pressure to shove the hydrogen atoms exactly between the sulfur atoms (of H3S, see figure)

Researcher Ion Errea at the Universidad del País Vasco / Euskal Herriko Unibertsitatea and Donostia International Physics Center used the quantum-wave nature of hydrogen to explain the superonducting structural properties of hydrogen-rich candidates for roo-temperature superconductors.

(Source: Universidad del País Vasco)

The principle researcher, Ion Errea at the Universidad del País Vasco (see photo) claims this new theoretical understanding is a "great step" toward the realization of room-temperature superconductors.

"Our computational work suggests that the recently discovered high-temperature superconductivity in the hydrogen sulfide system, which holds the record for the highest critical temperature, occurs in a structure that is stabilized by the quantum nature of the hydrogen atom," Errea told EE Times in an exclusive interview. "We mean that if the hydrogen atom was treated as a classical particle the atoms would arrange differently. Instead, when the full quantum character of the hydrogen atom is considered, that is, it is not considered as a point particle but described with a probability distribution function, the structure becomes a beautifully symmetric one. We believe that such quantum symmetrization is needed to explain the record superconductivity."

Structure of symmetric hydrogen bonds, induced by the quantum behavior of the protons, is represented by the fluctuating blue spheroids.

(Source: Universidad del País Vasco)

Errea readily admits that his theoretical breakthrough will not lead immediately to applications in the real world, because of the high-pressures needed to realize near room-temperature superconductors, but he does believe he has provided the scientific community with the tools it needs to achieve that goal.

"Our research, together with other theoretical works, underlines that new computational techniques provide a fantastic tool in the quest for room-temperature superconductivity," Errea told EE Times. "The ultimate goal will be to obtain a room-temperature superconductor at ambient pressures. The discovery of high-temperature superconductivity in sulfur hydride shows that room-temperature superconductivity might be possible in other hydrogen-rich compounds. This might be reached sooner than later at high pressures. However, obtaining room-temperature superconductivity at ambient pressure remains a huge challenge."

Next, Errea's group aims to begin formulating different hydrogen-based compounds to find which ones are predicted to have the highest superconductivity temperature, then test them in the lab to compare their experimental results.

"Our next step is to continue in the quest for high-temperature superconductors in hydrides making use of our computational techniques hand-in-hand with the experimental results," Errea told us.

Get all the details in the paper Quantum hydrogen-bond symmetrization in the superconducting hydrogen sulfide system.

— R. Colin Johnson, Advanced Technology Editor, EE Times

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