Radial correlation reflectometry measurements on the JET tokamak

Fluctuations and turbulence are believed to play an important role in anomalous transport of heat and particles in magnetic fusion devices. It is of vital importance to characterize transport mechanism in order to understand and control it. In correlation reflectometry (CR), two microwave beams with different frequencies are launched into the plasma from which the turbulence correlation length, $L_{r}$, and the density fluctuation level, $\raise0.7ex\hbox{${\tilde {n}}$} \!\mathord{\left/ {\vphantom {{\tilde {n}} n}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{$n$}$ can be deduced; quantities that are important for the study of plasma turbulence and transport. In this paper, some results of $L_{r}$ obtained with the four X-mode CR systems installed at Joint European Torus (JET) are reported. Experimentally, it was observed that $L_{r}$ increases from the plasma edge to the plasma core. Also, $L_{r}$ decreases inside the Internal Transport Barriers (ITB) [1]. The results obtained at JET agree quiet well with the $L_{r}$ dependence measured in other tokamak machines. [1] - A.C.A. Figueiredo, et.al., \textit{in the 34}$^{th}$\textit{ EPS Conference on Plasma Physics, Warsaw, Poland, 2-7 July, (2007)}.