Effects of fuelling profile on pedestal density profile

A series of experiments have been performed in DIII-D to investigate the roles of the deuterium ionization profile and radial transport in forming the density pedestal. These experiments used the range of divertor closures, obtainable in DIII-D, to vary the ionization profile in the pedestal with other discharge parameters held constant. The goal of these studies was to provide a systematic way to determine if the fuelling source has a direct effect on the density pedestal structure. The logic of these experiments was that an increase of divertor closure would lead to a reduction of fuelling within the pedestal. This reduction of core fueling from the more closed divertor was anticipated from previous analysis with UEDGE modeling that shows this result [1]. If core fueling was reduced, then measurements of pedestal profiles could be used to help understand the role of neutral fueling on the pedestal. Experiments were performed in discharges with 2 different equilibria, which had 2 different values of closure, shown in Fig. 1 [2-3]. A lower single null (LSN) shape, with the outer strike point on the lower shelf, provided the lowest closure (lowest baffling of neutrals by the divertor). An upper single null (USN), with outer strike point in the baffle of the upper outer cryopump (Fig 1), provided the highest closure (highest baffling of neutrals). Shapes of the two configurations were maintained as similar as possible. However, a higher triangularity was required for the closed divertor. The toroidal magnetic field BT direction was set so that the ion B x ∇B drift was towards the X-point for both configurations. For all discharges, BT was 2.1 T, plasma current IP was 1.3-1.4 MA and data were taken at injected beam powers Pinj of 3 and 5 MW. All discharges were run with long steady periods of all control parameters, including Pinj. A series of gas puff scans, with a )