Interferometric measurement of the sawtooth pre- and postcursor oscillations in Ohmic discharges on TEXTOR

The sawtooth activity of the electron density and temperature profiles in Ohmic discharges has been investigated in TEXTOR for a wide range of plasma parameters using a nine channel far-infrared interferometer and a ten channel ECE-radiometer. The m=1, n=1 precursor oscillation starts during the last 2-3 ms of the sawtooth ramp-up phase. The frequency slows slightly down while the amplitude increases. The outflow of density is poloidally asymmetric and correlated with the rotation of the helical m=1 perturbation. An oscillation with the same phase and frequency as the precursor which is apparent after the crash contradicts the full reconnection model. (orig.)