ECRH experiments in W VII A using different modes

In the W VII-A stellarator ECRH of OH-current-free plasmas at 28 GHz, 200 kW, 40 ms was investigated using the TE02, TE01, TE11 and HE11 modes as well as different wave-launching systems. The generation of the different modes in the transmitting waveguides is described. Discharges at optimum confinement conditions are compared. An increase of the central electron temperature is observed. Transport calculations show that this due to the narrowing of the power deposition profile. The heating efficiency can be explained by 0-mode single pass absorption only. The X-mode fraction does not contribute significantly to the global heating efficiency. For the TE11 (HE11)-case parametric decay of the X-mode pump wave near the UH-resonance layer occurs. Both decay wave spectra were measured and show a rapid drop near the lower hybrid frequency. Experiments with the ECR-layer off axis were performed