Abstract
The Tokamak a Configuration Variable (TCV) has a two channel correlation electron cyclotron emission (CECE) radiometer with a line of sight perpendicular to the magnetic field. The antenna pattern of this radiometer limits resolution to k < 112 m -1 or ks < 0.3 at 500 kHz. It can access the region with minor radius vol < 0.7. A series of measurements has been made of the turbulence spectra at positive and negative triangularity and as a function of collisionality. Also, a series of measurements has been made as a function of poloidal angle, by varying the plasma vertical position with respect to the antenna, the measurements being made on the same flux surface. It is planned to extensively upgrade the diagnostic by integrating four more channels and acquiring a new front-end for the radiometer. This upgrade should reduce the required number of shots for a radial scan by a factor four and improve the signal-to-noise ratio. It is also planned to use a high gain antenna that will extend access to kθ < 174m -1 or kθs < 0.5 at 500 kHz. The present system, measurements and the upgrade are described in this paper.
Highlights
Cross magnetic field transport of energy and particles in tokamak plasmas is larger than expected from Coulomb collisions
A series of measurements has been made as a function of poloidal angle, by varying the plasma vertical position with respect to the antenna, the measurements being made on the same flux surface
Correlation ECE (CECE) [2] measurements can elucidate the statistical properties of core electron temperature fluctuations in hot dense plasma and correlation electron cyclotron emission (CECE) is being increasingly used in magnetic fusion experiments
Summary
Cross magnetic field transport of energy and particles in tokamak plasmas is larger than expected from Coulomb collisions. Correlation ECE (CECE) [2] measurements can elucidate the statistical properties of core electron temperature fluctuations in hot dense plasma and CECE is being increasingly used in magnetic fusion experiments. Camenen et al [3] described the reduction of thermal diffusivity ( e) both by going from +ve to -ve and by increasing υeff ( ne ; for fixed Te and Zeff). Figure 1: thermal diffusivity shows a clear dependence on plasma shape (triangularity) and the effective collisionality. The CECE radiometer on TCV works using the spectral de-correlation technique [2]. By increasing the spectral distance of two channels, by virtue of the 1/R dependence of the magnetic field in the plasma, the spatial separation of the two channels increases. The current CECE radiometer, having only two channels, makes radial scans of channel separation rather time consuming
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