Phased array Doppler reflectometry at Wendelstein 7-X

A passive phased array Doppler reflectometry system has recently been installed in the Wendelstein-7X stellarator. In contrast to conventional Doppler reflectometry systems, the microwave beam can be steered on short time scales in the measurement plane perpendicular to the magnetic field in the range of +/- 25 degrees without mechanical steering components. This paper characterizes the design and properties of the phased array antenna system and presents the first measurement results from the latest OP1.2a campaign.