V-band Doppler backscattering diagnostic in the TCV tokamak

A variable configuration V-band heterodyne Doppler back-scattering diagnostic has been recently made operational in the tokamak a configuration variable. This article describes the hardware setup options, flexible quasi-optical launcher antenna, data-analysis techniques, and first data. The diagnostic uses a fast arbitrary waveform generator as the main oscillator and commercial vector network analyzer extension modules as the main mm-wave hardware. It allows sweepable single or multi-frequency operation. A flexible quasi-optical launcher antenna allows 3D poloidal (10 degrees - 58 degrees) and toroidal (-180 degrees to 180 degrees) steering of the beam with 0.2 degrees accuracy. A pair of fast HE11 miter-bend polarizers allow flexible coupling to either O or X mode and programmable polarization changes during the shot. These have been used to measure the magnetic-field pitch angle in the edge of the plasma by monitoring the backscattered signal power. Ray-tracing simulations reveal an available k(perpendicular to) range between 3 and 16 cm(-1) with a resolution of 2-4 cm(-1). Perpendicular rotation velocity estimates compare well against ExB plasma poloidal rotation estimates from charge exchange recombination spectroscopy.