MRI systems in the medical field are widely used, and it is already well known that great progress has been made in the development of superconducting technologies. Superconducting magnets are also being used for growing high-quality silicon single crystals. This is one example of the industrial application of superconductivity, illustrating that superconducting technologies have been able to meet many customer requirements. In this report, we present the history of the technological developments for these industrial applications of superconducting magnets.
In appreciation of a time relaxation behavior of critical currents as a result of flux creep in type-II superconductors, the possibility has been investigated that superconducting magnets may quench even in the persistent current mode. Because the time relaxation behavior of critical currents has been not observed directly, it has been thought as “the shadow, ” i.e., an implicit phenomenon. If a quench in the persistent current mode is experimentally confirmed, “the substance” of the time-dependent critical current will be grasped and then it appears explicitly. Experimental methods that can meet with quenches in the persistent current mode are proposed.
We have constructed a microwave resonator module using High Tc superconducting (HTS) thin films and a dielectric sapphire rod to measure microwave surface resistances of the HTS thin films. In this method the surface resistance is calculated from the measured unloaded Q values of the resonator. For precise measurements of surface resistance, therefore, the microwave loss not generated by HTS thin films must be minimized. By reducing the parasitic Q factors of the resonator module, we obtained Q values of as high as 1.2×107 at 17.3K and 12GHz. From the high Q values measured in this improved resonator, the surface resistance of the YBa2Cu3Oy superconducting thin films on MgO substrates was calculated and found to be 0.064 mohm at 20.2K and 12GHz.