Abstract
Coaxial helicity injection (CHI) has been successfully used in the National Spherical Torus Experiment for a demonstration of closed flux current generation without the use of the central solenoid. The favourable properties of the spherical torus (ST) arise from its very small aspect ratio. However, small aspect ratio devices have very restricted space for a substantial central solenoid. Thus methods for initiating the plasma current without relying on induction from a central solenoid are essential for the viability of the ST concept. CHI is a promising candidate for solenoid-free plasma startup in a ST. The method has now produced closed flux current up to 160 kA verifying the high current capability of this method in a large ST built with conventional tokamak components.
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