Density profile control with current ramping in a transport simulation of IGNITOR

Abstract

Current ramping to achieve reversed shear confinement enhancement and peaked density profiles are important for achieving ignition conditions in the high-field tokamak IGNITOR [Coppi et al., Phys. Scri. 45, 112 (1992)]. Previous transport simulations used either fixed density profiles or obtained flat density profiles leading to a conclusion that a mechanism for peaking the density profile is required for ignition. In this paper an enhanced particle confinement regime that produces ignition before the sawtooth activity begins is explored. It is shown that fast current ramping is a general scheme leading to density profile peaking. In these simulations, peaked density profiles result from the formation of internal transport barrier due to reversed magnetic shear, which is produced by controlled plasma current and volume-averaged density ramping. Such a programmed Ohmic heating scheme is demonstrated to be an effective approach to achieve ignition of a deuterium-tritium plasma.