Development of toroidal velocity and ion temperature shear during the IBW-induced, core H-mode in PBX-M

In this paper we examine the evolution of the gradients in toroidal velocity, V_φ, and ion temperature, T_i, during the CH-mode in PBX-M. This enhanced confinement mode develops from the H-mode following the application of IBW power and is characterized by strong density peaking and the formation of significant gradients in both toroidal velocity and ion temperature. The radial profiles of both the toroidal velocity and the ion temperature are obtained from the PBX-M charge exchange recombination spectroscopy (CHERS) diagnostic. A significant IBW power threshold is observed in the formation of the gradients. A power step of only 25 kW - from 200 to 225 kW - marks the onset. Details of the evolution of the gradients are given and, in particular, the variation with IBW power is described.