Scrape Off Layer Physics for Burning Plasmas and Innovative Divertor Solutions

Two distinct topics concerning SOL physics are examined. First, a novel magnetic divertor geometry is presented: 1) inducing a second axi-symmetric x-point downstream of main plasma x-point. For reactor relevant coils, field line lengths from the core x-point to the wall can be increased ~2-3 times, and flux expansion can be increased ~ 5 times. 2) the potential reactor consequences of large SOL convection from “bloblike” transport are examined for the first time. ARIES RS geometries have been simulated using UEDGE, including large convection in the far SOL similar to what is seen in experiments. The hot CX neutral spectrum at the wall is computed using the kinetic neutral code NUT. The high edge plasma temperature plus large recycling from blob-like SOL transport give highly enhanced sputtering for a tungsten wall from CX neutrals. Numerical simulations of 2-D nonlinear fluid equations describing blob turbulence from SOL resistive ballooning modes finds that impurities generated at the wall are rapidly convected inward toward the separatrix. Blob turbulence also greatly reduces the impurity screening of the SOL, leading to the potential for core radiation collapse in a tungsten wall reactor. Low Z liquid facing materials with low vapor pressure are examined and may provide acceptable alternatives.