Predictive numerical simulations on the formation of internal transport barriers in the reversed shear regime of KSTAR tokamak

Numerical simulations have been carried out to predict the formation of internal transport barriers (ITBs) in the reversed shear (RS) regime of Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak by using the ASTRA-1.5D transport code coupled with a simplified neutral beam injection (SINBI) code developed for this work. The present simulations employ a multi-mode transport model, MMM95, for anomalous transport calculations and use neutral beam injection for additional plasma heating and current drive. The simulations for the KSTAR plasmas reveal that ITBs are formed in the RS regime by control of E × B flow shear and by very low magnetic shear, and steep gradient regions apparently reside in both the ion and the electron temperature profiles. Suppression of plasma transport has been considered in this work in two ways: control of the coefficient deciding the strength of E × B flow shearing rate and addition of the effect of magnetic shear to the flow shear.