High-performance TF coil design for the Tokamak Fusion Core Experiment (TFCX)

The Tokamak Fusion Core Experiment (TFCX) is a proposed concept for an ignited, long-pulse, current-driven tokamak device. Toroidal field (TF) coil winding cross section in the inboard region is impacted by peak field (10 T), winding current density (∼3500 A/cm²), and peak nuclear heating rates (50 mW/cm³). The winding utilizes a Nb3Sn internally cooled cable superconductor (ICCS), which is a modified version of the conductor used in the Westinghouse Large Coil Program (LCP) coil. These modifications include the increase of void fraction from 32% to 41% of the cable space for withstanding higher nuclear heating rates and a thicker conduit wall to carry larger magnetic loads. The critical current of a Nb3Sn conductor is strongly dependent on strain in the superconducting strands. The strain in strands is lower when the windings are wound and then reacted (W/R), as compared to reacted and then wound (R/W). The impact of these approaches on winding performance is discussed. The windings are pancake wound and cooled with supercritical helium. The liquid helium (LHe) inlet (∼4 K) and outlet (∼5.5 K) connections are located on the sides of the TF coils. The conductor design, the winding design, and performance analysis are described.