Theoretical Study of the Effect of the Dynamic Ergodic Divertor on MARFE Onset

The effect of the TEXTOR Dynamic Ergodic Divertor (DED) on the formation of Multi‐facetted Asymmetric Radiation From the Edge (MARFE) is investigated. The thermal instability analysis accounts for the poloidal inhomogeneity of the background plasma equilibrium due to the Shafranov shift of the magnetic surfaces and the localized effect of the DED on edge transport and recycling; the influxes of working gas and impurity neutrals determined by plasma‐wall interaction; and the non‐coronal character of the impurity radiation, which depends on the perpendicular transport of impurity neutrals and radiant ion species. The model results in a Sturm‐Liouville eigenvalue equation for the poloidal dependence of perturbations. Numerical results for both carbonized and boronized TEXTOR walls are compared for the poloidally symmetric transport case and for various assumptions regarding poloidally inhomogeneous DED transport and conclude that the DED will decrease the MARFE onset density. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)