High temperature superconductor cable concepts for fusion magnets

Controlled nuclear fusion can be realized by confining plasma with high magnetic fields. High temperature superconductors have the potential to improve fusion magnets due to their superior mechanical properties, current density and critical temperature. Three concepts of high temperature superconductor cables carrying kA currents (RACC, CORC and TSTC) are investigated, optimized and evaluated in the scope of their applicability as conductor in fusion magnets. The magnetic field and temperature dependence of the cables is measured; the thermal expansion and conductivity of structure, insulation and filling materials are investigated. An improved contacting method is proposed to homogenize the contact resistances and the current distribution within the cables. Degradation-free impregnation with reduced thermal expansion epoxy resin is demonstrated. This technique prevents movement of the tapes and distributes mechanical loads. High temperature superconductor winding packs for fusion magnets are calculated and compared with corresponding low temperature superconductor cases.