J. Plasma Fusion Res. SERIES, Vol.l (1998) 176-179 Physics and Engineering Studies of a Helias Reactor

The current Helias reactor is an extrapolation of the W7-X configuration to reactor dimensions. This paper summarizes the computational results of various activities to improve the concept of the ad-vanced stellarator reactor: Forces and stress analysis of the coil system, self-consistent computation of plasma equilibria, a concept of divertor action on the basis of magnetic islands, neoclassical transport and investigation of alpha-particle confinement, start-up scenarios of the Helias reactor using ECRH and pellet injection and confinement studies using empirical scaling laws. Keywords: stellarator reactor, modular coils, ignition 1. lntroducton The main technical component of a Helias reactor is the magnetic system consisting of 50 modular coils. The magnet system comprises 5 field periods with 10 coils per period. In comparison to a previous design [1] the magnetic field on the coils has been reduced using a trapezoidal shape of the coil cross section and by re-ducing the average field by 5%. The winding pack is split into two parts in order to reduce the overall cur-rent density at the location of maximum magnetic field. The maximum field on the coils is now 10 T which is in the range of NbTitechnology at a temperature of 1.8 K. Furthermore, slight modifications of the coil ge-ometry have been made to account for the necessary space for blanket and intercoil suPPort elements. Each coil is enclosed in a steel case, which is designed as a box-type profile with a central web for mechanical stif-fening (Fig. 1). * Corresponding author's e-mail: wobig @ ipp- garching. mpg. d