Ouasi-Axisymmetric Stellarator GHS-qa

The physics aspects of CHS-qa, a quasi-axisymmetric helical device, which is being designed as the post-CHS device, are discussed. Its main objective is to improve the transport in helical systems by reducing the parallel viscosity and by applying max. J criterion to its design. The parallel viscosity is much reduced compared with that in CHS and the max. J criterion is fulfilled at the region near the edge in the typical CHS-qa configuration. As an experimental device, a variety of knobs for controlling magnetic field configuration are taken into consideration in the design to study transport-related physics subjects: bifurcation phenomena of radial electric fietd and max. J criterion. Other physics requirements which CHS-qa should satisfy as POP experiment, such as MHD characteristics, neoclassical transpon aspects, are also discussed.