Confinement Analysis of Spherical Tokamak-Stellarator Hybrid Configurations

To reduce reactor construction cost and to get good economic efficiency, it is desired to find out innovative magnetic configurations with compactness and high capability of confining fusion plasmas. We proposed 6 types of the compact spherical tokamak-stellarator hybrid configurations called TOKASTAR, which consists of a few simple spherical or cylindrical coil systems. We carried out magnetic flux surface analysis and equilibrium analysis for them by computational simulation with HSD and VMEC codes to understand their features of confinement capability. As the result, we obtained the TOKASTAR configuration with low-aspect-ratio (average value =1.2∼3.1) and high ellipticity, which leads to high equilibrium beta limit. Their flux surfaces form deep well depth (∼50%) but the average rotational transform is relatively low (< 0.1).