Prospect of Spherical Tokamak towards a Power Reactor -Challenge towards the Lowest Aspect Ratio Tokamak- 5. Can We Obtain the Realistic Power Reactor in the ST Approach? 5.2 Characteristics and Issues of Highly-Elongated Low Aspect Ratio Tokamak Equilibrium

Abstract

Characteristics of low-aspect-ratio tokamak equilibrium was studied to give a database for the spherical tokamak reactor design with an emphasis of attainable maximum elongation of divertor configurations. Effect of opening of the poloidal coil arrangement around the mid-plane of the machine was also verified. Controllability of the triangularity without center solenoid was analyzed for aspect ratios of 2, 4 and 6 covering spherical to normal tokamaks. At low aspect ratio, the triangularity is limited by the inflation of the plasma surface on the inboard side.