Development of a tunable multi-channel Doppler reflectometer on J-TEXT tokamak.

Doppler reflectometer is a powerful diagnostic tool to study the turbulence for tokamak plasmas. It can provide information on the density fluctuation, the poloidal rotation, the radial electric field, its shear, etc. A tunable multi-channel V-band (50-75 GHz) Doppler reflectometer system has been developed on the J-TEXT tokamak for the measurement under various toroidal magnetic fields. A universal serial bus controlled synthesizer is used as a source that can adjust the probing frequency remotely. This Doppler reflectometer can measure the plasma in 0.3 < ρ < 1 . Its radial resolution is <2 cm, and k is ∼ 4-12 cm. Based on the Doppler reflectometer, the perpendicular turbulence propagation velocity, the profile of the radial electric field, the geodesic acoustic mode, and some other phenomena have been observed on J-TEXT.