Options for the use of high temperature superconductor in tokamak fusion reactor designs

The use of high temperature superconductors (HTS) in long term tokamak fusion reactors is analyzed in this paper. The well-documented physical properties of high temperature superconductors are used in the evaluation. Short-sample wires and tapes of Bi2Sr2CanCun+1Oy materials, with n=1, 2 (referred to as BSCCO), and YBCO (YBa2CuO7−x) tapes approach their single-crystal performance limits. They provide a useful reference frame as well as a starting point of what may be possible in the future. In this paper, the design issues that arise when this technology is used in tokamak magnet applications will be investigated by extrapolating the properties of short sample YBCO thick films and BSCCO tapes to longer lengths. The properties of YBCO operating at elevated temperatures (>10 K) will also be summarized. The limitations imposed on the performance and lifetime of the HTS materials because of the fusion environment will be reviewed. The consequences of implementing an HTS configuration in a fusion environment will then be described. The use of HTS material may offer an opportunity for a fundamentally different approach to magnet design and construction leading to either lower cost or reduced maintenance. Reduced cost magnets requiring decreased shielding, with better access and easier maintenance may be feasible.