HTS coil shape optimization for its minimum volume condition

Sungkyunkwan University

@Wansoo Nah,Joon-Ho Lee, Joonsun Kang, Wansoo Nah, Il-Han Park , Jinho Joo

　 When we apply normal magnetic field to the flat surface of HTS tape, the critical current of the tape is substantially lower than that of parallel magnetic field to the tape surface. And the critical current of a coil usually shows reduced value in comparison with short sample data of the tape, the reason of which is mainly attributed to the normal magnetic field component to the flat surface of the local tapes. If we need to enhance the critical current of HTS coil, we have to reduce the magnetic field component normal to the tape surface at the coil ends. In this context, they proposed a shape optimal design method, which minimizes the maximum magnetic field to the tape surface at the coil ends [1]. In this algorithm, the object function was to reduce the radial magnetic field to the tape surface, and the superconducting characteristics, such as the Jc-B curves were not used as constraints: they used constant volume constraint. The calculated results showed that the final coil shape reduced the normal magnetic field component pretty much indeed, but it was also found that in some cases the central magnetic field itself reduces quite a lot [1], which seems to be a useless coil shape in practical point of view. In this paper we propose a new shape optimal design algorithm, in which the object function is to reduce the volume of the coil with subject to some fixed central magnetic field and Jc-B characteristics. The finite element method and continuum shape design sensitivity formula are employed for calculation of the sensitivity to the design variables. In this paper, the calculation processes as well as the final designed coil shape are presented.