Research and development of high-T _c SMES

High-T _c superconducting technology is thought to provide many merits for SMES systems. For example, a cry-ocooled system can be used as a cooling system for High-T _c superconducting coils, indicating that an operation temperature can be selected from a wide-temperature range below critical temperatures. Refrigerator cooling operation temperature for High-T _c SMES can be elevated more than 20 K from conventional 4.2 K. As a result, the heat capacity of coil system becomes much larger than that at 4.2 K, indicating that thermal diffusion time constant becomes much longer. If we could absorb transient heat generation with heat capacity of the coil, SMES systems can be designed under the over current state of critical current for a short duration. As a cooling capacity for an average heat load will be enough to cool High-T _c superconducting coil system for SMES, the refrigerator system cost can be much lower than that for a SMES system using Low-T _c superconductors. Moreover, we are developing high critical current superconducting wire for SMES system. The Bi2212 Rutherford conductors can carry 4 kA at 26 K under cryocooling. We also estimate the superconducting wire cost of the whole coil system, which is designed to minimize the superconductor volume. The conclusion is that the cost of High-T _c SMES system will be reduced by using the low-cost YBCO superconducting wires in the future.