Electron fishbones: Theory and experimental evidence

We discuss the processes underlying the excitation of fishbone-like internal kink instabilities driven by supra-thermal electrons generated experimentally by different means: Electron Cyclotron Resonance Heating (ECRH) and by Lower Hybrid (LH) power injection. The peculiarity and interest of exciting these electron fishbones by ECRH only or by LH only is also analyzed. Not only the mode stability is explained, but also the transition between steady state nonlinear oscillations to bursting (almost regular) pulsations, as observed in FTU, is interpreted in terms of the LH power input. These results are directly relevant to the investigation of trapped alpha particle interactions with low-frequency MHD modes in burning plasmas: in fact, alpha particles in reactor relevant conditions are characterized by small dimensionless orbits, similarly to electrons; the trapped particle bounce averaged dynamics, meanwhile, depends on energy and not mass

Plasmoid drift during vertical pellet injection in FTU discharges

Abstract MHD and plasmoids are key elements in pellet injection experiments on FTU. The plasmoid drift can take particles from the pellet ablation region to the q=1 surface in high field side (HFS) pellet injection on FTU. Then MHD reconnections could take density from that region to the plasma center. A strong MHD event would be triggered by the injected pellet in high current (1.1 MA) discharges. A preliminary comparison between the post-pellet experimental density profile in low current discharges (0.8 MA) and the result of a pellet ablation code is presented. Strong magnetic fluctuations develop during pellet ablation. They may be Alfvén waves generated by the drifting plasmoids, preliminary results are shown