Measurements of ion temperature fluctuations in the tokamak fusion test reactor

First of a kind measurements of high-frequency ion temperature microturbulence in fusion-grade plasmas have been made in TFTR. The ion temperature 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, (T̃/T)/(ñ/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 modes in the turbulent spectrum. The temperature fluctuation spectra were found to exhibit a narrow transition region between distinctive edge and core turbulent modes, as has been seen with ion density fluctuations. The ratio of the relative fluctuation levels is greater than unity across this transition, which suggests that, despite the different modes present, the underlying instability is driven by the ion temperature gradient.