Radial-poloidal correlation of electron temperature fluctuations at W7-AS

Stefan Bäumel
IPP Garching, Germany

2D-ECE correlation measurements have been performed, supplementing earlier temperature fluctuation measurements. The 2D-ECE correlation diagnostics at W7-AS consists of four poloidally staggered radial sightlines with eight channels per sightline. Structures were found, which are elongated in radial and poloidal directions. These structures show a higher coherency in poloidal than in radial direction and are found to be moving in electron diamagnetic drift direction. They are thought to be of the drift-wave type of fluctuations. Scaling experiments show, that electron temperature fluctuations decrease with increasing ECRH heating power, in agreement with earlier studies. The vanishing of the structures can be attributed to an increasing velocity shear, which arises from higher radial electric fields with increasing heating power. This tears the structures apart to smaller scale lengths, then too small to be detected by the two-dimensional ECE-correlation diagnostics.