Construction of a 7-T Force-Balanced Helical Coil

Abstract

Force-Balanced Coil (FBC) is a helically wound toroidal coil that can minimize the required mass of its structure by selecting an optimal number of poloidal turns per toroidal turn. A 7-T Force-Balanced Coil (7-T FBC) was designed in order to demonstrate the feasibility of the FBC concept for high field superconducting magnets. The 7-T FBC with an outer diameter of 0.53 m will have 270-kJ stored magnetic energy at maximum magnetic field of 7.0 T. This coil is a hand-made coil using NbTi superconductor. The maximum working stress of the 7-T FBC is lower than the elastic limit of the Cu matrix so that the 7-T FBC can be excited up to the rated magnetic field of 7.0 T without reinforcing materials for the NbTi strand. The winding form is made of aluminum alloy and slots are cut on its surface with the shape of the helical winding with a numerically controlled (NC) lathe. The experiments will be conducted with pool boiling liquid helium cooling in order to measure the quench properties of the 7-T FBC and evaluate the working stresses in the helical windings.Index Terms-Electromagnetic force, helical coil, high field magnets, NbTi, the virial theorem.

Development of a One Tenth Sized Model Coil for 100-MJ Class SMES Using Force-Balanced Coil Concept

“…From the results of the cooling test, the detachment of the junctions and the significant deformations of the winding form have not been observed. windings is estimated to be 52 MPa at the maximum magnetic field of 7.0 T [5]. This stress is lower than the elastic limit of the Cu matrix [6], [7], so that the model FBC may be excited up to 7.0 T without reinforcing materials, such as stainless steel wires, for the NbTi strand.…”

“…The objective of this work is to demonstrate the feasibility of the FBC concept for large-scale SMES using a model coil based on the FBC design. The model FBC with an outer diameter of 0.53 m will have the stored energy of 270 kJ at the maximum magnetic field of 7.0 T using NbTi superconductors [4], [5]. This size of the FBC will be one tenth size of the 150-kWh SMES coil when the maximum magnetic field is 15 T. This paper describes the design considerations, the winding techniques and the demonstration plan of the model FBC.…”