Search for alpha-driven TAE modes at lowered ion temperature in TFTR DT discharges

An experiment was performed in TFTR DT plasmas to attempt to destabilize the alpha particle driven Toroidicity-induced Alfven Eigenmode (TAE) by transiently cooling the ions, which should have lowered the ion Landau damping of the TAE modes. Transient cooling perturbations were made during the NBI heating phase of high powered DT supershots using He gas puffs or deuterium (D) or lithium (Li) pellet injection. The ion temperature was successfully lowered from Ti(O) ∼ 20 keV to Ti(O) ∼ 10 keV in about 0.2 sec; however, no signs of alpha-driven TAE modes were observed. Theoretical analyses of these discharges suggested that the alpha pressure required for TAE instability was about a factor of 2--3 greater than actually obtained in this experiment, consistent with the absence of alpha-driven TAE modes