Doppler reflectometer system in the stellarator TJ-II

Abstract

A Doppler reflectometer system has recently been installed in the stellarator TJ-II. The system is optimized for the Q-band (33-50 GHz) and the high-curvature plasmas produced in TJ-II. The launch angle of the microwave beam can be controlled by a steerable mirror to obtain angles between +/-20 degrees enabling the measurement of perpendicular wave numbers in the range of 3-15 cm(-1). The available angular range allows for comparisons between positive and negative values and additionally for calibration of the system. Localization and k(perpendicular)-estimation is done via the three-dimensional ray/beam-tracing code TRUBA. First measured spectra and radial profiles of the perpendicular velocity of plasma density fluctuations are presented.