EXPERIMENTAL STUDIES OF THE LINK BETWEEN PRODUCTION AND PENETRATION OF IMPURITY ATOMS INTO THE PLASMA EDGE AND THE CENTRAL IMPURITY CONTENTIN TEXTOR-94

Characteristic quantities for impurity release from limiters and the p enetration of atoms into the plasma boundary have been determined by o ptical methods on the tokamak TEXTOR-94. The velocity distribution of neon atoms released from a tungsten limiter has been measured. A drast ic increase of fast particles could be observed in comparison to the v elocity distribution of neon released from-a carbon limiter under comp arable conditions. As a result the penetration depth of neon increased by a factor of 1.7. The influence of local electron density and tempe rature near the limiter has been demonstrated for various species as H e, C, Ne, Si and Mo comparing different central electron densities. Bo th penetration depth and neutral fueling efficiency decrease with incr easing density. For high Z materials such as Mo prompt redeposition of singly ionized ions is found to be of major importance. The measured radial profile of the ion source distribution of molybdenum under neut ral beam heated conditions has been used to calculate the Mo-density i n the plasma center for different line averaged central electron densi ties (n) over bar(e), taking into account both the ionization processe s inside and outside the LCFS. The decrease of the calculated Mo-densi ty with (n) over bar(e) is in agreement with the experimentally observ ed variation of the central Mo-density.