Spatio-temporal diagnostics of plasma fluctuations with probe arrays and statistical techniques
In this work advanced diagnostic techniques, used to analyze plasma turbulence fluctuations, are investigated and optimized. For this reason diagnostics based on Langmuir probes such as 2D-probe arrays and conditional averaging method, used for spatio-temporal investigation of plasma fluctuations, are analyzed. First, the capabilities of probe-arrays are tested under well-defined conditions with synthetic data and experimental data from the linear KIWI device. It turns out, that the spatial resolution of standard probe-arrays is too low for advanced turbulence investigations. For this reason super-resolution algorithm known from computer vision for image resolution enhancement is adapted to 2D-probe arrays. Further, prospects and limitations of conditional averaging techniques are investigated on synthetic data and turbulence data from the Blaamann experiment. Although conditional averaging method shows an apparently high spatial and temporal resolution using just two probes, the averaging process implies that only the average temporal evolution is observed which can be quite different from real turbulence dynamics, e.g. dipolar structures can be distorted to appear as monopoles. To understand the physical processes resolved by these diagnostics, a comparison of their results on similar plasma conditions from KIWI turbulence regime is made. It is shown that conditional averaging gives reliable results only for local approximation around the reference probe while by super-resolving of the 2D-probe array data the global evolution is obtained.