Real-Time Wall Conditioning Experiments in the Wide Pedestal QH-Mode Regime

Wide Pedestal QH-Mode (WPQH-Mode) in DIII-D is an intrinsically non-ELMing enhanced confinement regime (H_98y2 up to 1.6) with a higher and wider pedestal regulated by broadband turbulence. Compatibility with future burning plasma conditions includes zero net NBI torque throughout and up to 77% electron-cyclotron heating without degradation. Previous studies show core impurity transport is favorable in WPQH-Mode. However, carbon content is higher than ELMy H-Modes, possibly due to increased carbon sputtering from high boundary temperatures or pedestal transport. Here, controlled injection of boron and lithium powders at measured rates during WPQH-Mode discharges successfully reduced carbon concentrations during injection without degrading confinement. Boron resulted in a cumulative wall conditioning effect. Nitrogen injection was particularly effective in reducing carbon content while radiating from the divertor. Densities of carbon, boron, lithium, and neon were measured by charge exchange recombination spectroscopy. Lithium in the upper divertor was observed by tangential TV camera. Divertor heat flux profiles comparing Standard and Wide Pedestal QH-Mode within the same discharge were measured by Langmuir probes and IR cameras using strike point sweeps.