SMES Optimization for High Energy Densities

Abstract

High critical temperature superconductors (HTS) bring a lot of opportunities for SMES (Superconducting Magnetic Energy Storage). The large current densities under very high fields and the mechanical strength of IBAD route ReBaCuO coated conductors are very favorable characteristics. Electricity storage still is an issue in general and SMES bring a very interesting solution for pulse current supplies especially if its energy density increases. The record for SC magnet is 13.4 kJ/kg today. We study how to enhance this value. One of the main limitations for the SMES energy density is the mechanical stress as shown i.a. by the viriel theorem, which links simply stress and energy. The current density is another limitation not only the critical characteristic. Indeed protection also plays an important part and often is the real limitation for LTS magnets. We optimized solenoids with mechanical stress and current density constraints. 20 kJ/kg requires current densities of the order of 400 and stresses of about 400 MPa. These values are compatible with YBCO data but pose protection difficulties, which should be perhaps rethought. The design and these protection issues are discussed.