System design of the heliotron-type reactor FFHR

In order to clarify the design window and the design strategy toward a DEMO and a commercial reactor of heliotron system, the systems code for LHD-type heliotron reactors HELIOSCOPE was developed based on the experimental achievements of the Large Helical Device (LHD) and the knowledge from the conceptual design study of the LHDtype helical reactor FFHR. HELIOSCOPE has been utilized for the conceptual design activity and improved by the feedback of the knowledge from the design activity. According to the design window analysis with the most recent knowledge, it was found that a helical DEMO or commercial reactor is foreseeable as an extension of the present achievements by selecting the major radius of 4 times of LHD. The design parameters which have a strong effect on the design window were indicated. In particular, increase in space for blanket can significantly expand the design window and leads to the design possibility of a low size, low cost DEMO reactor.