Dimensionally exact form-free energy confinement scaling in W7-AS

A semi-empirical theory for global energy confinement in the stellarator W7-AS is presented. It employs elementary rules of probability theory together with the transformation properties of the basic equations describing plasma behaviour. The semi-empirical theory allows model comparison between four different kinetic plasma models. The analysis is applied to the 153 t approximate to 1/3 W7-AS data documented in the international stellarator database. It is found that the collisional low-beta kinetic model describes best the physics of W7-AS energy confinement. Finally, the predictive power of the semi-empirical theory is successfully tested in the prediction of the energy content in (single variable) density and power scans performed in W7-AS.