First Evidence of Collective Alpha Particle Effect on Toroidal Alfvén Eigenmodes in the TFTR D-T Experiment

The alpha particle effect on the excitation of toroidal Alfv\'en eigenmodes (TAE) was investigated in deuterium-titrium (D-T) plasmas in the Tokamak Fusion Test Reactor. rf power was used to position the plasma near the instability threshold, and the alpha particle effect was inferred from the reduction of rf power threshold for TAE instability in D-T plasmas. Initial calculations indicate that the alpha particles contribute 10%--30% of the total drive in a D-T plasma with 3 MW of peak fusion power.