Probe Systems for W7-X

The new large stellarator W7-X equipped with a divertor is currently under construction in the Greifswald branch of the Max-Planck-Institute for Plasma Physics. It is planned to begin the plasma operation with a variety of diagnostics to analyse the expected properties of the concept and explore the capabilities of the new machine. In the framework of divertor and edge plasma diagnostics a number of electrical probes will be exposed to monitor particle fluxes, electron temperatures and potentials in the vicinity of the divertor targets as well as up-stream. W7-X is intended to operate in quasi-stationary regime with a large power input. The open island divertor has to handle the high particle fluxes and the peak power flux to the targets. Consequently, fast movable mechanisms are designed to cyclically expose and retract the probes. Four pneumatically driven arrays of single probe tips are planned for the horizontal and vertical parts of one upper and lower divertor module, respectively. The probe tips are designed to avoid the problem of shallow angles with the magnetic field, to tolerate the impinging power, to be adjustable in their radial position and exchangeable without dismounting the targets. Additionally, a small number of basically identical linear manipulators are planned for different locations around the stellarator with exchangeable diagnostic heads (fast moving probe, Mach probes, emissive probes, retarding field analysers, collector probes, etc). The main design problems of the probe systems and results from prototype tests are reported. (