High Z material operation in FTU

High Z materials, as possible plasma facing components for a fusion
reactor, are being re-evaluated due to their advantages connected to the
low sputtering yield and small erosion. A data base of experimental
results related to their use on present Tokamak is missing. FTU has
carried out a series of experiments with different medium and high Z
limiter materials, Ni, Mo, and W, to improve the knowledge of the plasma
behavior in these conditions. The results on plasma operation, core
parameters, impurity content, and corresponding radiation losses are
presented, and compared with those obtained with a low Z dominant
impurity (siliconization). A simple model coupling the SOL and the
plasma core is able to reproduce the experimental results, indicating
that sputtering and self-sputtering are the main physical mechanisms of
impurity production.