Island divertor in a helical-axis heliotron device (Heliotron J)

A new configuration with ι/2π ∼ 0.5 is proposed as an island divertor configuration in Heliotron J, a small size l=1/M=4 helical-axis heliotron device. In this case, both the m=8/n=4 edge islands and the last closed flux surface can keep simultaneously the moderate size. As a first step of an island divertor design with this configuration, edge field characteristics are numerically investigated assuming a target plate at rtarget=0.33 m (5 cm inside from the chamber wall). It is shown that the divertor fields cross the target at four discrete regions per a field period. The connection length from the edge to the target plate is in the range of 50–400 m. The total value of the `wetted areaʹ for the whole torus is about 600 cm2. The incidence angle of the diverted field lines to the target plate is less than 10°.