Formation and sustainment of a 150 kA tokamak by coaxial helicity injection

Abstract

Coaxial helicity injection is used to produce low-aspect-ratio tokamaks with toroidal currents reaching 150 kA (highest value yet attained by helicity injection current drive) and sustained over 100 kA for many resistive diffusion times, without a current drive transformer. Current drive power efficiency, assuming no anomalous helicity dissipation, is 40% that of Ohmic. These tokamaks have a rotating n=1 toroidal distortion, with poloidal distortions only on the outer bad-curvature region. Equilibrium reconstruction suggests these plasmas have up to 112 kA of closed-field toroidal current, an aspect ratio A=1.69, a tokamak q profile, and a hollow toroidal current profile.