An investigation of beam driven Alfvén instabilities in the DIII-D tokamak

Neutral beams were injected into low field (B = 0.7-1.0 T) deuterium plasmas in an attempt to destabilize toroidicity induced Alfvén eigenmodes (TAE modes). When the parallel beam velocity approached the Alfvén velocity and the volume averaged beam beta exceeded 2%, localized, propagating modes with n = 2-10 were observed. As much as 45% of the beam power was lost as a result of the modes. The threshold for TAE instability is at least one order of magnitude higher than that predicted by Fu and VanDam (Phys. Fluids B 1 (1989) 1949).