Confinement characteristics of the quasi-axisymmetric stellarator CHS-qa

A low aspect ratio stellarator CHS-qa with a quasi-axisymmetric configuration has been designed at NIFS, whose main objective is the experimental study of confinement improvement. The high beta equilibrium was obtained with the HINT code which does not require the assumption of nested magnetic surfaces. The equilibria with bootstrap current were calculated using the SPBSC code and their global MHD stability was evaluated with the TERPSICHORE code. The boundary structure of the magnetic field was examined to scope divertor options. A new method of calculating the neoclassical transport properties was developed for toroidal configurations with very small non-axisymmetry. The control knobs of the configuration properties are proposed for the study of improved confinement. (author)