Laser-induced fluorescence in the edge of fusion plasmas

Laser-induced fluorescence (LIF) has been applied successfully to measurements in the edge of high-temperature plasmas for a long time, especially in both mainstream types of magnetic confinement devices, tokamaks and stellarators. Typical relevant ranges of plasma parameters are ne 1018-1020 m-3 for the electron density and Te = 1-100 eV for the temperature. In the field of plasma-wall interaction, current needs stress the importance of pieces of equipment that allow rapid and smooth exchange of plasma-facing components (vacuum-lock systems), an arrangement with which LIF becomes extremely flexible and can actually be used routinely. Various examples of in situ measurements will be presented, which emphasize the special role of LIF in the recording of velocity distributions and density profiles of neutrals - particularly of light atomic species - in the boundary of fusion plasmas and illustrate the corresponding findings. Sensitivity, space and time resolution will be discussed on the basis of these examples. A short outlook, including possible developments for existing or future devices, like W7-X, will be presented. (author)