Low- and high-power measurements on a remote steering upper port launcher mockup for ITER

The Euratom association FOM-Rijnhuizen is developing a plug-in 170 GHz ECW launcher system for use in the upper-ports of ITER, based on the remote steering (RS) principle, designed to stabilise the neoclassical tearing modes (NTM) at the q=3/2 and q=2/1 surfaces by inducing off-axis current drive. The launching system enables up to eight mm-wave beams per port plug to be directed from the feeding waveguides through corrugated square waveguides (≈ 44×44 mm²) inside the port plug to the plasma. A mock-up system has been manufactured, capable of vacuum & high-power short-pulse operation. The transmission line consists of a taper, to launch an HE₁₁ mode in 63.5 mm circular corrugated waveguide. (The taper will be replaced by a gyrotron source in high power testing). The circular waveguide is used as input for the steering mechanism, housed in a vacuum vessel, which directs the beam under an angle between -12° and 12° through the CVD diamond window into the copper square corrugated waveguide. Antenna patterns from the exit aperture of the square waveguide are scanned using a 3-axis scanner. Low-power measurements (Takahashi et al., 2003) are a preparatory phase for high-power tests, currently prepared in FZK. In the low-power measurements, waveguide performance will be inferred from antenna pattern measurements. Of interest are slight differences in beam parameters (angle, waist etc.) relative to the input beam.