Plasma Edge Diagnostics for TEXTOR

The exploration of plasma-wall-interaction physics is one of the major tasks of the tokamak TEXTOR. A characterization of the high-temperature plasma edge is essential to interpret the interaction processes of the different charged and uncharged particles in the boundary layer. In the design of the TEXTOR, much effort was made to optimize diagnostic access to the plasma edge for the best possible characterization. The major part of the plasma edge diagnostics presented here is based on passive and active spectroscopy, in addition to different types of electrical probes. Thereby, pioneering work has been achieved in both fields.

In passive emission spectroscopy, the work concentrated on the determination of particle fluxes of different types of atomic (W, Si, C, . . .) and molecular (D₂, CD, C₂, . . .) species from the corresponding photon fluxes at different locations and on the visualization of the local impurity sources by means of two-dimensional imaging. The active spectroscopy with atomic beams was focused on the determination of plasma edge parameters (n_e, T_e, T_i, . . .) with good spatial and temporal resolution. Therefore, different techniques like thermal Li and He beams, suprathermal Li beams - realized by laser blow-off techniques - and hydrogen neutral beam injectors have been employed. Furthermore, laser-induced fluorescence measurements in the ultraviolet and in the vacuum ultraviolet ranges, which were for the first time performed in a fusion plasma, are presented. The continuous improvement of the different plasma edge diagnostics over more than a decade of TEXTOR plasma operation with different types of first-wall materials is discussed.