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The superconducting stellarator Wendelstein 7-X has completed the first three experimental phases, the first one with a limiter only and two phases with an inertially cooled carbon divertor configuration. The main mission of the latter two phases (the last one with two scraper elements) was to pave the way for the planned steady-state operation with high-power plasmas and a steady-state divertor. Presently, the device is being completed by installing a high-heat-flux (HHF) divertor and the corresponding water-cooling and ten cryo pumps in the divertor chambers. After this completion phase of W7-X, the device is ready for long-pulse divertor operation with heating power beyond 10 MW. [ABSTRACT FROM AUTHOR]

The magnetic confinement of plasmas in fusion experiments can significantly degrade due to perturbations of the magnetic field. A precise analysis of the magnetic field in a stellarator-type experiment utilizes electrons as test particles following the magnetic field line. The usual fluorescent detector for this electron beam limits the provided information to two-dimensional cut views at certain toroidal positions. However, the technique described in this article allows measuring the three-dimensional structure of the magnetic field by means of close-range photogrammetry. After testing and optimizing the main diagnostic components, measurements of the magnetic field lines were accomplished with a spatial resolution of 5 mm. The results agree with numeric calculations, qualifying this technique as an additional tool to investigate magnetic field configurations in a stellarator. For a possible future application, ways are indicated on how to reduce experimental error sources. [ABSTRACT FROM AUTHOR]