DEALS: a demountable superconducting magnet system for fusion reactors

Abstract

A new type of superconducting magnet system (DEALS) for large fusion reactors is described. Instead of winding large planar or multi-axis coils, as has been previously proposed in fusion reactor designs, the demountable superconducting coils would be made by joining together several prefabricated conductor sections. Conductor types, fabrication processes, and joining schemes are described. The magnet sections would be made at a central factory and shipped to the reactor site for assembly. The magnetic forces on the conductors would be transmitted to an external room temperature support structure via low thermal conductivity bearing blocks. This reduces conductor tensile stresses to very low levels. Differential and mechanical thermal movements between the magnet coil and the external support structure would be accommodated by the use of moveable joints between magnet sections. These pressure type contact joints carry current during magnet operation, and do not carry tensile loads. Finite element analyses on the magnet and its support structure are presented together with analyses of magnet cooling requirements. Results of experiments on small movable pressure type joints at liquid helium temperatures are described. These indicate that adequately low joint losses should be achievable in large magnet systems. Current carrying capcity is not affected by relative motion, and friction coefficients are reaonable. Based on these results and the analyses, the DEALS concept appears feasible for fusion magnet systems.