kspectra of Thomson scattering temperature profiles at the TJ-II stellarator

High resolution Thomson scattering temperature profiles at the TJ-II stellarator are subjected to spectral analysis. The obtained k spectrum is very robust in shape. While its amplitude has been shown previously to scale inversely with the collisionality, here it is found that its shape is independent of plasma configuration (magnetic well, iota), global plasma parameters (temperature, density) and radial position (centre, edge). The shape is also found to be very similar to that of k spectra obtained with Langmuir probes in the edge of TJ-II and of k spectra obtained using other techniques in other devices. The spectral shape is characterized by a `knee' at k = 500-1000 m -1 and a steep decay at large k. Self-similarity analysis reveals the existence of a high degree of self-organization dominated by structures of around 2.5 cm in size.