HTS Magnets: Opportunities and Issues for SMES

SMES (superconducting magnetic energy storage) devices are an attractive solution for pulsed current sources. However, the specific stored energy is moderate and has to be improved. High temperature superconductor (HTS) materials offer opportunities in terms of current carrying capabilities as well as mechanical strength. We report the optimization of solenoids with regards to mechanical stress and current density constraints. 20 kJ/kg requires current densities above 150 MA/m² and stresses of about 400 MPa for energies in the range of 5 to 50 MJ. The optimization code makes possible the study of the influence of different parameters such as the maximum allowable magnetic field. A method is proposed to discriminate space of solution. The best configuration is achieved keeping in mind the peculiar properties of HTS tape (which impact protection of SMES), and the specifications of the application. Parallel to these theoretical approaches, we are developing the magnet technology by first realizing small magnets we test under very high fields (up to 18 T) to apply the large mechanical stresses.