Recent Mach probe measurements of the bulk ion toroidal velocity near the last closed flux surface in DIII-D (Müller et al 2011 Phys. Rev. Lett.106 115001) are consistent with the existence of a loss-cone distribution in velocity space, as described previously (deGrassie et al2009 Nucl. Fusion49 085020), predicting a co-Ip directed velocity localized to the edge. The former model has been extended into the scrape-off layer and takes into account limiting surfaces, and is also extended to include the effect of a uniform radial electric field with magnitude and sign relevant for measurements in the edge of DIII-D H-mode conditions. These added effects modify the details but do not wash out the basic model-computed velocity profile.
The ion velocity distribution in a toroidal plasma