Preliminary Design of DEMO PF Coils Based on EU DEMO 2018 Baseline

The dimensioning of Winding Packs and allocation of materials in DEMO PF coils is proposed based on the requirements defined by the EUROfusion 2018 DEMO baseline. The coils are pancake-wound and use two types of forced flow cable-in-conduit conductors. The conductor which uses NbTi has a high void fraction but has no separated low-impedance cooling channel. On the other hand, the conductor made using Nb3Sn has a separated low-impedance cooling channel and therefore low void fraction in the remaining cable space. Both the conductors have a rectangular cross-section. The design addresses the dimensioning of the Winding Pack (WP) based on the electromagnetic field calculations and stress analysis. The amount of superconductor, copper, and cable void fraction in the conductor are determined by the coil current, magnetic field and assumed temperature margin. The amount of structural material in the conductor jacket depends mainly on the fatigue stress corresponding to the pulsed operation of these coils. For PF1 and PF6 coils, the comparison of NbTi and Nb3Sn design options suggest a more efficient allocation of structural and superconducting material in the latter case. The WP dimensions do not significantly depend on the winding technique (pancake vs layer winding).