Comparison of theoretical models for scrape-off layer widths with data from COMPASS-D, JET and Alcator C-Mod

The features of a number of theoretical models proposed to explain the cross-field transport in the SOL are summarized. Simple balances of transport parallel and perpendicular to the magnetic field in the SOL allow the derivation of predictions from these models for the power law scalings of the SOL width D with the plasma parameters in the two cases of a collisionless and a collisional SOL. Data on the SOL widths for a collisionless SOL from COMPASS-D and for a collisional SOL from JET and Alcator C-Mod are then used to test these models. Remarkably, the data from COMPASS-D, JET and Alcator C-Mod all favour the same small subset of these models. Furthermore, direct comparisons of the theoretical models for the cross-field Athermal diffusivities with SOL data from JET and Alcator C-Mod provide some support for this finding. These `best modelsʹ can be used to make predictions for MAST, the spherical tokamak at Culham Science Centre, and for ITER.