MEASUREMENTS OF ION TEMPERATURE-FLUCTUATIONS IN THE TOKAMAK FUSION TEST REACTOR

First of a kind measurements of high-frequency ion temperature microtu rbulence in fusion-grade plasmas have been made in TFTR. The ion tempe rature fluctuations and carbon density fluctuations were found to have spectra, similar to those of the ion density fluctuations across the plasma radius. The ratio of the relative fluctuation levels, ((T) over tilde/T)/((n) over tilde/n), is 2 +/- 0.5 from r/a = 0.59 to r/a = 0. 99. The fact that this ratio is greater than unity is consistent with the general expectations of ion temperature gradient driven turbulence theory and suggests that ion drift modes dominate trapped electron mo des in the turbulent spectrum. The temperature fluctuation spectra wer e found to exhibit a narrow transition region between distinctive edge and core turbulent modes, as has been seen with ion density fluctuati ons. The ratio of the relative fluctuation levels is greater than unit y across this transition, which suggests that, despite the different m odes present, the underlying instability is driven by the ion temperat ure gradient.