Characterization of the DIII-D Scrape-Off Layer During the Application of Resonant Magnetic Perturbations using the Thermal Helium Beam Diagnostic

Electron density and temperature profiles have been measured in the scrape-off layer using the thermal helium beam (THB) diagnostic at the DIII-D tokamak during the application of resonant magnetic perturbations (RMPs) and the introduction of various impurities. The THB is designed to work specifically in the edge region, where other diagnostics may suffer due to optically thin plasmas. The THB works by puffing a small amount of neutral helium into the device, and uses line ratio spectroscopy of observed helium lines and a collisional radiative model to yield electron temperature and density over the lifetime of a shot. It has a diagnostic range covering typical scrape-off layer (SOL) parameters, 1x10¹⁸ m^-3< n_e < 1x10²⁰ m^-3 and 10 eV < T_e < 200 eV, and a 10 ms time resolution. Edge behavior is significantly impacted by the application of external resonant fields, creating a 3D structure in the SOL, and possibly introducing significant changes in both density and temperature. Recent experiments at DIII-D focused on transport of He and Ne and their impact on the SOL in the presence of RMPs, during which several THB measurements were collected. This contribution presents the details of the THB diagnostic setup, an experimental summary, and edge profiles from a series of RMP plasma conditions. In combination with edge modeling, data from this diagnostic will give a better understanding of scenarios long-considered essential to future fusion pilot plant longevity and success.