Identification and Modeling of Plasma Edge Helicity in QSH states on MST*

Edge modeling efforts are enabled by knowledge of the plasma parameters in the edge and scrape-off layer plasma. The quasi-single helicity (QSH) state necessitates a 3D model of the edge due to its helical nature. Recent measurements with probes in MST 425 kA QSH plasmas have provided needed plasma parameters, and revealed an edge pressure bulge that matches the orientation of the core helical mode. The edge plasma temperature ranges from 75 eV in the edge to 40 eV in the SoL when the mode is locked to the measurement location, while the temperature profiles are flat at 20 eV otherwise. Density drops off an order of magnitude from edge to SoL in both cases, with the absolute value higher when the QSH mode is locked over the probe. Probes measure the plasma flux to the limiters and, combined with ongoing camera measurements, constrain the recycling coefficient on the limiters to 0.85 ± 0.07. These measurements now constrain EIRENE simulations used to obtain energy losses of the edge plasma via neutral interactions. Simulations show that neutrals can represent a significant minority of total plasma energy losses, of about 20 − 45% under various QSH conditions. Exhaust pathways will be presented in detail.