Extrapolation of the W7‐X Magnet System to Reactor Size

Abstract

The fusion experiment Wendelstein 7-X (W7-X), presently under construction at the Greifswald branch institute of IPP, shall demonstrate the reactor potential of a HELIAS stellarator. HELIAS reactors with three, four and five periods have been studied at IPP since many years. With a plasma axis induction of 5 T, corresponding to about 10 T maximal induction at the coil, it was shown that such reactors are feasible. Now the possibility is being investigated to increase the conductor induction up to the 12 T -range, corresponding to > 5.5 T at the plasma axis. This improves the stellarator confinement properties but does not change the basic physics with respect to the previously analyzed machines. In particular the 5periodic HELIAS type, HSR5, is considered which evolves from W7-X by linear scaling of the main dimensions by a factor of four.Recent progress in superconductor technology and the extensive development work performed for ITER are taken into account. The latter is particularly relevant since by coincidence the circumferences of the HSR5 and the ITER toroidal field coils are practically the same. For the presented 12 T reactor version, the HSR50a, also the conductor and structural requirements are comparable to the corresponding ITER specifications. Therefore, advantage can be taken of these similarities for the stellarator reactor magnet design.The input was provided by the new code "MODUCO" which was developed for interactive coil layout. It is based on Bézier curve approximations and includes the computation of magnetic surfaces and forces.

Structural analysis of W7-X: From design to assembly and operation

“…In addition, the obtained experience is a basis for stellarator reactor studies in IPP [24,25]. Original block before cut Modified block Fig.…”

Coil winding pack FE-analysis for a HELIAS reactor

“…Consequently, the stellarator field configuration and thus the basic plasma physics remain the same. The upgrade from HSR5/22 to the new "HSR50a" concerns the increase of induction from ≈5 T to ≈5.6 T at the plasma axis corresponding to ≈10 T and ≈12 T, respectively, at the maximally loaded coil conductor [8].…”

“…This comparison suggests itself to base a first HSR5 coil design iteration upon the ITER TFC and to transfer the extensively developed ITER-technologies wherever applicable. It was demonstrated that ITER's superconductor and winding pack concept, including electrical insulation, can be adapted to HSR50a, as well as the electrical design concerning power supply, voltage levels and quench protection [8].…”

“…For instance, one could align the section normal vectors n of a coil parallel to a plane from which the 3D-deflections are minimal [8], or parallel to one which contains the torus axis and the coil centre of gravity (CG). This would allow conductor bending around axes parallel and perpendicular to n only, and yield rather smooth coils of the Types 3, 4, and 5 which have moderate curvatures.…”

“…Other options are agnet system structure Fig. 4 shows the double shell structure [8] with improvements and larger port windows. The stress intensity is low within most of the structure with only some local maxima exceeding the standard allowable membrane plus bending stress limits of typically 750 MPa for steel 316 LN which is acceptable.…”