Plasma Turbulence

Due to a dramatic drop in plasma temperature, plasma turbulence leads to high energy losses in fusion devices. Plasma probes are the best suited diagnostic tools for measuring plasma potential and electron and ion temperature. Cold Langmuir probes (CLP) can only derive these parameters with low temporal resolution from the current-voltage characteristics. The floating potential of cold Langmuir probes is also not of advantage, because this parameter depends strongly on the electron temperature. Together with colleagues from DTU and ENEA, R. Schrittwieser, C. Ionita et al. (University of Innsbruck) have developed probes with the floating potential close to the plasma potential so that the latter parameter can be measured directly and with high temporal resolution. These plasma potential probes are either electron-emissive probes (EEP) working in all types of plasma or electron screening probes whose principle is based on the difference between the gyro radii of electrons and ions in magnetic fields. For comprehensive investigations of blobs in the SOL of medium-size tokamaks (ASDEX Upgrade, TCV, MAST) a new probe head was developed which combines several probes and two retarding field analyzers (RFA) for ion energy distribution measurements. The probe head also contains two magnetic pickup coils (MPC) to measure magnetic field fluctuations.