Test in Strong Background Field of a Modular Element of a REBCO 1 MJ High Energy Density SMES

A superconducting magnetic energy storage (SMES) is a promising technology for pulse power current source. Nevertheless, they have modest specific energy. Taking advantage of new possibilities offered by the impressive performances of second generation high-temperature superconductors (HTS) tapes in liquid helium, the BOSSE project has the objective to build an SMES with a specific energy of 20 kJ/kg in the MegaJoule range (present world record is 13 kJ/kg). To reach such a high specific energy, high levels of stress and current density are required. A full-size prototype pancake, made of a 139-m-long insulated HTS conductor, has been tested in background magnetic field up to 8 T in Grenoble LNCMI. The objective was to test the mechanical limits of the pancake and to demonstrate the possibility to protect an HTS pancake at high current density, thanks to voltage measurement. A protection system dedicated to the experimental setup is described. It allows us the protection of the pancake at an overall current density of 691 A/mm 2 (i.e., 984 A/mm 2 bare tape engineering current density) and under noisy background field due to the resistive outer magnet. The analysis of the measured signals and mechanical performance of the pancake are presented.