Examination of the velocity time-delay-estimation technique

The one-dimensional time-delay-estimation (TDE) velocity technique infers the velocity of plasma fluctuations using cross-correlations between two spatially separated signals, and here this technique is evaluated using experimental results and numerical simulations. Probe arrays and a fast-framing imaging camera are used to measure the azimuthal fluctuation propagation speed in a cylindrical magnetized plasma device. The time-averaged TDE velocity field obtained in this way is found to be approximately 30% larger than Mach probe measurements of the plasma fluid velocity, suggesting that the TDE method infers the plasma E × B velocity and presumably a diamagnetic flow. The TDE technique is also applied to turbulent simulation data with known velocity fields. The results show that for the TDE parameters chosen here, the TDE technique can be used to infer the large-scale, slowly varying velocity, but that small scale or turbulent velocity fields cannot be reliably inferred.