Magnetic fluctuations on TFTR

Abstract

Data from magnetic pickup loops (Mirnov coils), located on the wail inside the vacuum vessel of TFTR, are used for studying the edge magnetic fluctuations. Experiments, such as impurity injection, gas puffing, and plasma motion, dramatically affect the fluctuations measured by the coils. A quantitative study of the fluctuation levels during these experiments has been made. Results show that there are simple relations between the amount of impurities or gas injected and changes in the fluctuation levels. Spatial locations of the fluctuation modes have also been tentatively identified. Finally, different models were studied in order to explain the behaviour and dependence of the fluctuations on the relevant parameters of the plasma.

Evidence and concepts for non-local transport

“…Thus, it seems that the stability and behaviour of the core 1/1 MHDlike modes change in concert with, but are not the cause of (see figure 2) the non-local rising core electron temperature, even before any other local parameters (gradients, density fluctuations, equilibrium potential, see preceding paragraph) change. We speculate that there could be changes (decreases, like those observed in edge magnetic fluctuations [17]) in the (unmeasured) medium mode number (m/n ∼ (3-30)/(2-20)) magnetic fluctuations in the core region of the plasma which somehow influence core electron heat transport and modecouple to the 1/1 MHD-like modes causing them to change in concert with the non-local core electron transport response. In this sense, magnetic phenomena may play a role in the non-local effects.…”

“…(The 'edge' (r/a = 0.7) fluctuations approximately doubled as the normal inwarddiffusing cold pulse propagated through that region [13,16]. Further, on TFTR [17] and Evidence and concepts for non-local transport B181 TEXT [13] the edge magnetic field fluctuations decreased in concert with the edge cooling. Thus, the increases in local edge diffusivity induced by an edge cold pulse could indeed be caused by changes in the local electrostatic turbulence over approximately the outer half of the plasma [13].…”

“…However, if other, coupled plasma parameters (e.g., current profile, ion temperature or turbulence) moved much faster than diffusive electron heat transport, they could induce such an apparent non-local effect-see sections 6 and 7.) Re-examination of TFTR [17,18] (and TCA tokamak [19]) data showed that such non-local responses to abrupt edge cooling were also often present there as well, primarily for ohmically heated plasmas. The studies of non-local cold-pulse transport responses observed in TEXT and TFTR are highly complementary and have now been significantly extended [16,18,20,21].…”