Formation of internal transport barriers in Globus-M tokamak in regime with early neutral heating beam switch-on

Abstract

A series of experiments have been performed on the Globus-M spherical tokamak under conditions with additional plasma heating by a beam of neutral atoms at the stage of plasma current buildup. This regime allowed a region with negative magnetic shear to be formed in the inner plasma region adjacent to the magnetic axis. Under these conditions, the stability margin coefficient at the axis was greater than unity. This scenario of plasma heating leads to the transition to a regime of improved confinement with the formation of a broad temperature profile and peaked electron density profile due to the formation on internal barriers. Results of experiments and numerical simulations of transport processes using the ASTRA code are presented.