W7-X performed three experimental campaigns, the last one (OP1.2b) featuring among others high density, high power, low Z
eff detached plasmas kept stable over tens of seconds. Meanwhile several tens of diagnostic systems are in operation at W7-X, quite a number of them used for spectroscopic observation of the plasma edge. Due to the inherent 3D topology of the magnetic islands plasma observation in only one poloidal plane insufficient. This results, in combination with the limited port access for plasma observation, in complex setups of diagnostic hardware and analysis tools. Selected diagnostic methods based on passive and active spectroscopy will be presented together with their implementation at W7-X and with the information they provide about important parameters determining the W7-X island divertor plasma behaviour. Moreover, some of the spectroscopic signals were used in the last campaign as input for feedback-controlled gas injection. Results of the precise control and stabilisation of the detached plasma state over the longest high-power detached discharge in W7-X, to date, will be presented.
[mehr]