Vacuum fields and parameter range of a modular Helias configuration

At IPP Garching, the stellarator experiment WENDELSTEIN VII-X is being developed. Among stellarators Helias configurations (Helical Advanced Stellarator) offer the prospects of stable plasma operation at (β)∼5% because of the optimization of confinement, MHD-equilibrium and stability. Considering ballooning modes and resistive interchange instability, Helias configurations with five field periods are preferred. In the present paper the development of a modular coil system for W VII-X is described briefly, and details of the magnetic vacuum fields and the accessible parameter range are given. We concentrate on a data set named HS 5-8 with a major radius of 6.5 m and a coil aspect ratio of 5.4. Each of the 60 coils, considered to be superconducting, carries 1.75 MA at a current density of about 50 MA/m2. The magnetic field on axis is 3 T and the maximum induction at the coil is 5.8 T. (author) 6 refs., 6 figs