Heterodyne radiometer at Rijnhuizen Tokamak Project for electron cyclotron emission and absorption measurements

The 20-channel heterodyne radiometer of the Rijnhuizen Tokamak Project (RTP) measures microwaves in the range between 86 and 146 GHz. The spatial resolution is ∼7–16 mm parallel and 25–1300 mm2 perpendicular to the viewing direction, depending on the position in the torus. A waveguide network gives the opportunity to do alternate measurements of X- and O-mode electron cyclotron emission (ECE) from the low-field side (LFS) and X-mode ECE from the high-field side (HFS). A backward wave oscillator is installed at the HFS, for the purpose of measuring the electron cyclotron absorption (ECA) of the plasma. This set-up also provides a possibility for fast relative calibration of the radiometer. To reduce the effects of multiple-pass reflections and standing waves, Macor viewing dumps are mounted at both sides. A comparison of HFS and LFS ECE measurements during electron cyclotron heating will be given as a first result. First results of ECA measurements were obtained but will be presented in the future.