Influence of the LTS Outsert Shape on AC Losses in a REBCO HTS Insert

A superconducting magnet system composed of a REBCO high-temperature superconducting (HTS) insert and low-temperature superconducting (LTS) outsert has been designed and fabricated. When the HTS insert is charged up/down or exposed to an alternating magnetic field, it will suffer large ac losses which impart a negative effect on the thermal stability of the superconducting magnet system. The influence of the LTS outsert shape on ac losses was investigated. The calculations are carried out in three steps. First, the Fabry's coil-shape factor was adopted to design the LTS outsert. The inner radius, the outer radius, and the height of the LTS outsert were varied independently to obtain the configurations with the same center magnetic field, albeit of different shapes. The magnetic field dependence of the REBCO tape's Ic-value was introduced accordingly. Secondly, the ac losses generated in the HTS insert were studied based on a slab model, which takes the temperature variation into consideration. Thirdly, the results for ac losses with different LTS outserts were compared and discussed through three different cases.