Marfes are toroidally symmetric bands of radiating plasma that form at the smaller major radius side of tokamaks. A model of marfes and density limit is studied. Though very simple, the model provides alternative explanation of the marfe onset beyond the density limit, explains the marfe poloidal location, states that a marfe can onset only when the criterion ( in /q)2 chi /sub // approximately /< (To/TL)2 chi perpendicular to is satisfied, where To is the central temperature and TL approximately 10eV is the temperature of intensive impurity radiation. Density fluctuations observed in marfe experiments are explained as the manifestation of sound waves which are intermediate between the isothermal and adiabatic.
Experimental observation of Marfes in the W7-AS stellerator