Global influx and impurity behaviour during ICRF heating in JET with beryllium gettering and beryllium limiters

During ICRF heating in JET with Be gettering and Be-belt limiters the impurity influxes are significantly reduced as compared to the all carbon case. The dominating 'global' influxes originate at the limiters and wall and are consequence of the increased power flow in the scrape-off layer (SOL). The 'RF specific' influxes from the torus internal surfaces, far away from the antenna, are not observed. Zeff=1.5-2 is routinely achieved at power levels up to Prf=15 MW and with the Be limiters even at densities =(1-2)x1019 m-3. The dilution is nd/ne>0.8. Zeff scales inversely with density and weakly with RF power, (Zeff-1)∝PRF0.4-0.6/0.9-1.1. Prad/Ptot is 50% lower than previously observed. Even at densities =(4-6)x1019 m-3 the radiated fraction is below 30% of input power. In the case of Be gettering and carbon limiters the dominant impurity is carbon. With the Be limiters it is replaced by Be. The oxygen is eliminated in both cases. The density is controlled by the pumping of deuterium and the recycling coefficient Rd is less than one during the entire rf pulse. The density limit observed in the all carbon phase was exceeded by a factor 2-4. Volume averaged density =1x1020 m-3 was achieved with gas puffing at power PRF=8 MW. (orig.)