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 cros s-field transport in the SOL are summarized. Simple balances of transport p arallel and perpendicular to the magnetic field in the SOL allow the deriva tion of predictions from these models for the power law scalings of the SOL width Delta 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 fora collisional SOL from JET and Alcator C-Mod are then use d to test these models. Remarkably, the data from COMPASS-D: JET and Alcato r C-Mod all favour the same small subset of these models. Furthermore, dire ct comparisons of the theoretical models for the cross-field thermal diffus ivities with SOL data from JET and Alcator C-Mod provide some support for t his finding. These 'best models' can be used to make predictions for MAST, the spherical tokamak at Culham Science Centre, and for ITER.