April 12, 2016

Mastering superconductors and high field trapped field magnets

EEtimes has more details about improved superconductor theories

"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.

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.

"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.

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