Power modulation experiments in JET ITB plasmas

Power modulation experiments are a well known tool to investigate electron heat transport and have been widely used in conventional L-mode or H-mode plasmas. In this paper new results are presented of power modulation experiments in JET plasmas characterized by strong electron and ion Internal Transport Barriers (ITB). The modulated power source is RF ICRH power in mode conversion scheme, which takes place in D plasmas with 3 He concentrations of 10-20% Experimental Results Two RF deposition schemes have been explored: a) 3 He concentration ~12% (mixed minority heating and mode conversion), which led to the best ITB performance; b) 3 He concentration ~20% (full mode conversion regime), which allowed the best transport studies. Maximum care needs to be taken when performing the FFT analysis of T e modulation data to derive profiles of A and j. In fact an intense MHD activity is often present in these plasmas, with frequent crashes due to internal kink modes (typically m=2, n=1). These crashes if included in the analyzed time interval generate a broad low frequency spectrum (0-25 Hz) which is peaked in space at the ITB radius and pollutes the real heat wave signal