Turbulence radial correlation length measurements using Doppler reflectometry in TJ-II

First measurements carried out using radial correlation Doppler reflectometry in the TJ-II stellarator are presented. Broad scans in the probing beam angle are performed to study the behaviour of the radial correlation length measured by Doppler reflectometry. A comparison with the simulation results obtained using a two-dimensional full-wave code (Blanco and Estrada 2013 Plasma Phys. Control. Fusion 55 125006) indicates that both linear and non-linear regimes are found. In linear regimes, the procedure to calculate the best estimation for the turbulence radial correlation length found in the simulations is applied providing sensible results. These measurements, viewed as a validation of the simulation results, show that Doppler reflectometry provides a good estimation of the turbulence radial correlation length in linear regimes if the probing beam angle is scanned. (letter)