OBLIQUE AND CORRELATION ECE IN TCV

The Tokamak à Configuration Variable, TCV, is equipped with a moveable ECE receiving antenna, identical to the 6 second harmonic (X2) ECH/ECCD launchers, which can track the plasma at any position within the vacuum vessel in real time. In contrast to this poloidal plane viewing, the receiver can be rotated to obtain an oblique view. In this configuration, measurements of the asymmetry of the electron distribution function, EDF, are performed during co/counter ECCD sweeps at constant input power. Direct evidence of the driven current is provided by the ratio of radiation temperatures from co and counter views of identical plasmas. The results are simulated by the NOTECTCV radiation-transfer code in which current profile broadening can be included to reproduce the measurements. Studies of core broadband temperature fluctuations, induced by plasma turbulence, are performed with a high-resolution X2 correlation ECE diagnostic. ECE correlation is measured by two frequency-tunable YIG filters that can be placed between r/a = 0 - 0.9 using both their wide tuning range, and plasma geometry changes from shot to shot. Evidence of broadband (20–150 kHz) fluctuations with peak frequencies ranging from 20 kHz up to 90 KHz at r/a = 0.3 - 0.8 in Ohmic sawtooth-free discharges was obtained. The amplitude of the temperature fluctuations decreases with increasing density and thus, increasing collisionality, which is in qualitative agreement with predictions from quasi-linear gyrokinetic calculations performed with the gyrokinetic code GS2. The mixing length heat diffusivity calculated from GS2 decreases with increasing collisionality, as does that obtained from a power balance analysis. The real frequency of the broadband turbulence stays positive over the range of collisionalities explored, indicating dominant TEM turbulence.