Transient coaxial helicity injection (CHI) has been successfully used in the helicity injected torus-II and the National Spherical Torus Experiment (NSTX) for a demonstration of closed-flux current generation without the use of the central solenoid. The Tokamak Simulation Code (TSC) has now been used to understand the scaling of CHI generated toroidal current with variations in the external toroidal field and injector flux. These simulations show favourable scaling of the CHI start-up process with increasing machine size. Closed flux in TSC is achieved as a result of the decaying CHI discharge that induces a positive loop voltage generating the initial closed-flux current.
Non-inductive current generation in NSTX using coaxial helicity injection