Experimental Study of Repetitive ST Plasma Merging by use of Oscillating Poloidal Coil Currents

Abstract

Repetitive merging of spherical tokamak (ST) plasma was demonstrated in the TS-4 device using oscillating poloidal field (PF) coil currents. The oscillating induction current is transformed into plasma currents of small ST plasmas, if its polarity satisfies the Shafranov condition. This natural rectification was found to form repetitively small ST plasmas with single helicity, and their merging gradually drives the plasma current of the main ST plasmas.