Solenoid-Less Plasma Start-Up in NSTX Using Transient CHI

Abstract

Experiments in NSTX have now unambiguously demonstrated the coupling of toroidal plasmas produced by the method of transient Coaxial Helicity Injection (CHI) to inductive sustainment and ramp-up of the toroidal current. The coupled discharges have ramped up to 700 kA and transitioned into H-mode with low inductance typical of the type of discharges needed for long-pulse operation, demonstrating the compatibility of the CHI startup method to conventional inductive operation used since the start of tokamak research. The method was first demonstrated on the smaller concept exploration device HIT-II at the University of Washington. These new results that were obtained on a machine built with mainly conventional components and on a size scale closer to a Component Test Facility, demonstrate that CHI is a viable solenoid-free plasma startup method for future STs and Tokamaks.