Numerical modelling of MARFE phenomena near the bumper limiter of TEXTOR-94

It has been observed on TEXTOR-94 that; the spontaneous development of MARF Es, poloidally localized intensively radiating regions of cold dense plasma , is caused by plasma cooling due to impurity radiation and due to the hydr ogen recycling at the inner bumper limiter of TEXTOR tokamak. In this paper we present results of numerical modelling performed in the sp ecific geometry of TEXTOR-94 in order to study the relative importance of d ifferent physical mechanisms in the MARFE development. Calculations were do ne by using several 2D transport codes (B2-EIRENE and TECXY) to judge the s ignificance of particular processes. The present extensive calculations con firm the idea that a MARFE development can be triggered solely by localized recycling, when the last closed magnetic flux surface is close enough to t he bumper limiter and certain critical conditions are fulfilled.