Search for Alpha-Driven TAE Modes at Lowered Ion Temperature in TFTR DT Discharges
Authors: S. J. Zweben, R.V. Budny, C.Z. Cheng, E.D. Fredrickson, G. Y. Fu, D. R. Mikkelsen, G. L. Schmidt, S. D. Scott, D.A. Spong, C.E. Bush, Z. Chang, D.S. Darrow, R. Fonck, L. Grisham, E. Mazzucato, R. Nazikian, D.K. Owens, H. Park, S. Paul, J. Schivell, J.D. Strachan, E. Synakowski, G. Taylor, and K. M. Young
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(0)Å20 keV to Ti(0)Å10 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.