Reflectometry measurements of the m=1 satellite mode in L- and H-mode plasmas in ASDEX

In ASDEX, with strong NBI heating often a large central m=1, n=1 mode is observed on the SXR emission. For PNBI ≅ 1 MW a mode rotating with the same frequency, the so-called 'm=1 satellite', is seen on the magnetic pick-up coils in the L- and H -phases. Magnetic measurements in the divertor chamber suggest that the satellite mode might be located outside the separatrix, on open field lines reaching the divertor. Here we present results from localized microwave reflectometric measurements. The time evolution of the satellite mode frequency is studied for plasmas with different qa and the mode localization is estimated, confirming that it should be close to but outside the separatrix. The central toroidal rotation velocities of the plasma can be inferred from the measured frequencies of the satellite modes. (author) 4 refs., 5 figs