Design considerations for force-balanced coil applied to SMES

Strong electromagnetic force caused by high magnetic field and large coil current is a serious problem in superconducting magnetic energy storage (SMES) systems. In facing this problem, we propose the concept of force-balanced coil (FBC) which is a helical-winding toroidal coil and can reduce the centering force of toroidal field coil (TFC). The helical-winding of the FBC is modulated in order to reduce the torsional force. This paper describes the cost-related parameters of the FBC in terms of the dimension of the coil, the ampere-meters of superconductors and the surface area of the coil compared with the TFC and the solenoid. Moreover, we discuss the structure requirements by the virial theorem and improve the concept of FBC in terms of the further optimization of SMES through the structural analysis.