Trends of W behavior in ICRF assisted discharges in ASDEX Upgrade

During Ion Cyclotron Range of Frequencies (ICRF) operation with metallic plasma facing components, plasma wall interaction processes are modified, which needs to be understood in order to reduce the ICRF-related rise in impurity concentration and maximize ICRF coupling. This contribution is focused on gathering and analyzing a database on W-behavior during ICRF spanning a multi-parameter space. The gas puff dependence is investigated in selected pulses that feature the injection of deuterium (D₂) main gas, with impurity gas nitrogen (N₂), argon (Ar) and krypton (Kr). C_W was found to decrease with the total gas injection rate, which was also correlated with the changes of electron density in the location of the C_W measurements. Although the addition of N₂, Ar and Kr impacted on the increase in sputtering, to achieve a similar C_W level with mixed puffing, one needs to inject considerably more gas. Moreover, C_W is shown to change after implementation of boron coatings on the ICRF antenna limiters