A 2 mm microwave scattering system was used on TEXTOR to observe density microfluctuations with good space and time resolution. In ohmic heating conditions, a turbulent sawtooth precursor was discovered and studied in detail near the q = 1 surface, the large fluctuation spike occurring at the sawtooth crash was precisely located in the mixing region, and it was shown that a turbulence pulse propagates together with the outgoing heat pulse. In sawteeth-free neutral beam injection heating discharges, evidence of a toroidal Doppler effect was collected suggesting short parallel wavelength fluctuations near the magnetic axis. In sawtoothing neutral beam injection discharges, a strong transition of the MHz fluctuation levels during the sawtooth development appears as new evidence of the link between confinement and fluctuations.
Microwave imaging reflectometry for density fluctuation measurement on KSTAR