Variations of force-balanced coils for SMES

Strong electromagnetic force caused by high magnetic fields and coil current is a serious problem in superconducting magnetic energy storage (SMES) systems. In facing this problem, we proposed the concept of the force-balanced coil (FBC) which is a helically wound toroidal coil applied to SMES. This paper shows the variations of the helical windings in order to reduce structure requirements. We discuss the relationship between the shape of SMES coils and the structure requirements based on the virial theorem. From this result, the FBC can minimize the working stresses by selecting the optimal number of poloidal turns.