Construction of 320-kJ superconducting force-balanced coil

Strong electromagnetic force caused by high magnetic fields and coil curren t is a serious problem in Superconducting Magnetic Energy Storage (SMES) sy stems. To cope with this problem, we propose the concept of Force-Balanced Coil (FBC) applied to SMES. The PBC is a helical-winding torus coil that ba lances the centering force with the hoop force, both of which are exerted i n the major radius direction. In the case of FBC, the toroidal current dist ribution is modulated so that one of the magnetic surfaces coincides with t he torus surface in order to reduce the torsional force. This current distr ibution can be achieved by varying the helical winding pitch. However, the smaller the aspect ratio (= major radius / minor radius), the more difficul t it becomes to manufacture the varying helical windings. To overcome this difficulty, we developed a winding machine which can modulate the helical w inding. We also designed an experimental superconducting FBC which is being manufactured using the winding machine.