Abstract
We study the effect of lower hybrid waves on edge turbulence using a set of two Langmuir probes inserted in the scrape-off layer of the Tore Supra tokamak. We use the cross-correlation coefficient to assess the interplay between turbulence and the LH waves. We found that turbulence is affected at high plasma current even at relatively low LH powers. When the plasma current is below 1 MA, this effect disappears. Finally, we show that the level of fluctuations and the cross-correlation amplitude are correlated whereas the increase of the first leads to the increase of the second. The role of the plasma current could reflect that the exchange of the RF waves with edge turbulence is occurring in the closed field lines rather in the open field lines range.
Highlights
The interaction between the radio frequency (RF) waves and the edge turbulence has resurfaced recently after experimental results showing that turbulence in the SOL decreases when the ion cyclotron frequency heating (ICRH) is switched on [1,2]
Some tokamaks (FTU & HT-7) have shown a net decrease of turbulence [3,4] while others (Tore Supra) did not [5,6]. We showed that these apparent discrepancies among tokamaks and RF wave frequencies were removed where it is found that turbulence largescale structures in the scrape-off layer decrease at high enough plasma currents (Ip) on the Tore Supra tokamak [7]
In agreement with our previous publications, the present results show the important role of the plasma current in the way the lower hybrid (LH) power affects edge turbulence
Summary
The interaction between the radio frequency (RF) waves and the edge turbulence has resurfaced recently after experimental results showing that turbulence in the SOL decreases when the ion cyclotron frequency heating (ICRH) is switched on [1,2]. The main goal of this paper is to show that at turbulence large-scale structures decrease when both the lower hybrid power and the plasma current are moderately high. We shall correlate the level of turbulence to the amplitude of the cross-correlation coefficient and deduce that at both the plasma current plays an important role in the interaction between the RF waves and edge turbulence. This leads to a change in the confinement properties as we show by comparing the dependence of the diamagnetic energy on the plasma current at low vs high RF power
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