Double-Null Divertor Design for JT-60SU, A 10-MA Class Long-Pulse Tokamak

The design of a double-null divertor for use in JT-60SU is presented. The free-boundary equilibrium code EFIT is used to establish a symmetric highly triangular double-null plasma shape. The baffle shapes are highly contoured to match the equilibrium, with the plasma-facing surfaces intersecting the flux surfaces at steep angles in the regions of high heat flux. These contoured surfaces also provide a tightly baffled design with small-aperture pumping gaps near both the inner and outer divertor strike points. The gaps provide adequate throughput of D₂ gas for active control of impurity entrainment at reasonable pressures. The structural design is shown to be consistent with both forces from disruptions and thermal stress during vacuum vessel bakeout.