Spectroscopic Diagnostics of Tokamak Edge Plasmas

The characterisation of the plasma edge in Tokamaks is essential for the interpretation of the interaction processes of the different charged and uncharged particles in the boundary layer. Spectroscopic techniques are valuable tools for the investigation as they do not disturb the plasma and can provide both data for the particle influx (species, direction, and velocity distribution) and parameters of the surrounding plasma. Passive emission spectroscopy allows particle flux determinations of different types of atomic and molecular species from the corresponding photon fluxes at different locations and on the visualisation of the local impurity sources by means of 2D imaging. Active spectroscopy with atomic beams can serve to determine plasma edge parameters ( n e , T e , T i ...) with good spatial and temporal resolution. Also, various techniques such as thermal Li and He beams and suprathermal Li beams—realised by laser blow-off techniques—are employed. Laser-induced fluorescence measurements in the UV and in the VUV make the investigation of hydrogen and medium- Z impurities possible.