Correlation Ece Diagnostic on Tore Supra to Study MHD Instabilities Related to Fast Particle Dynamics

Temperature fluctuation diagnostics are being used to detect and study the fast particle instabilities, which could destabilize Magnetohydrodynamic (MHD) modes in tokamak plasmas. As the thermal noise is higher than the temperature fluctuation amplitude, correlation of two adjacent Electron Cyclotron Emission (ECE) channels is needed to recover the electron temperature fluctuations using long time integration. On Tore-Supra, we are developing a multi-channel ECE correlation diagnostic to observe MHD modes at 4 plasma positions with a radial resolution of about 2 centimeters and the poloidal resolution of about 4 cm (1/e folding width). A 1-channel prototype using 2 band pass YIG filters has experimentally identified MHD instabilities related to fast particles dynamics. This first channel is currently being upgraded to reduce crosstalk and a second channel will be operational in 2008. The probing frequencies can be changed during the discharges, with 1 s dead time between two modifications. Programmable attenuators are used to optimize the signal dynamic according to the frequency sensitivity. At nominal condition (B=3.8 T), the diagnostic accessibility covers the outer plasma part up to a normalized radius r/a=0.2 on the inner side. Two more channels will be implemented in 2009 and will allow us to measure the radial profile of MHD modes, or to study their inner/outer side asymmetry. (authors)