From Wendelstein 7-X to a Stellarator Reactor

Wendelstein 7-X is a drift-optimized stellarator with improved thermal and fast ion confinement. Additional optimization criteria are a stiff equilibrium configuration and MHD stability up to a volume averaged β of 5 %. The main objectives are to demonstrate reactor-relevant plasma performance under steady-state conditions including power and particle exhaust with an island divertor. To that effect Wendelstein 7-X has superconducting coils with a maximum average magnetic field of 3 T and will be equipped with actively cooled plasma facing components for heat fluxes of up to 10 MW/m2. Besides fulfilling this research mission, the extrapolation from Wendelstein 7-X to a stellarator reactor is an important issue. The capability of such an extrapolation will depend also on the results from other stellarators, on the ITER results and here in particular the experience gained with α-particle heating and operating a nuclear device, and the advancement of first-principle theory required for the extrapolation.