Turbulent fluctuations in the main core of TFTR plasmas with negative magnetic shear Page: 4 of 9
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2.60 2.64 2.68 2.72 2.76
FIG. 3. Time evolution of density fluctuations in the ERS mode. The shaded area represents the time
density and plasma pressure profiles (Fig. 1). Since at the time of bifurcation the q-
profiles are very similar in the two regimes, the observed phenomenon cannot be
ascribed solely to the negative magnetic shear.
A transport analysis, ignoring particle pinches, shows a greatly reduced plasma
transport in the ERS mode (Fig. 2). In particular, the precipitous drop of the ion
thermal conductivity inside the reversed shear region to values below those of
conventional neoclassical theory  reveals the formation of a transport barrier.
2. Turbulent Fluctuations
Short scale turbulent fluctuations have been studied with X-mode microwave
reflectometry in the frequency range 123-142 GHz . Figure 3 shows the time
evolution of density fluctuations at two radial locations inside the negative shear
region of an ERS plasma. From these results, it appears that large bursts of turbulence,
initially present in the discharge, disappear after the transition into the ERS mode.
By using the displacement of the reflecting point of the probing wave, caused by
the plasma density rise, we get the amplitude of density fluctuations shown in Fig. 4 as
a function of the normalized minor radius r/a. The abscissas in this figure are the
0.0 0.1 0.2 0.3 0.4
FIG. 4. Amplitude of density fluctuations in the ERS mode of Fig. 1 at t=2.72-2.78 s; ra, is the
radial position with minimum q.
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Mazzucato, E.; Beer, M. A.; Bell, M. G. & Batha, S. H. Turbulent fluctuations in the main core of TFTR plasmas with negative magnetic shear, article, September 1997; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc694329/m1/4/: accessed September 26, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.