Factors Determining Decay-Index Distribution and Contribution of a Central Solenoid on a Spherical Tokamak

Abstract

Factors that dominate achievement of the decay-index (or N-index) distribution required for highly elongated divertor plasmas with large triangularity are studied. The outermost coil is regarded as a leading candidate, but can supply only a part of the equilibrium value. Current in Central Solenoid with the same direction as the outermost coil current is found to fill the difference of the decay-index distribution on the mid-plane between the equilibrium magnetic field and the outermost coil field.