Verification tests of critical bolted connections of the W7-X coils

The functionality of the most critical bolted connection between a coil and the central support structure of the Wendelstein 7-X (W7-X) magnet system was mechanically tested on full-scale mock-ups. The object of the test campaign was to verify the final design, in particular the load capability of the connection. Special attention was drawn to its individual components (bolts, sleeves, and spherical washers) and the assembly steps, here especially the positioning and welding of wedges. Furthermore, the instrumentation foreseen for bolts on W7-X was studied. ecutive series of tests was performed using mock-ups equipped with modified components. Each test sequence included activities at ambient temperature (assembly, bolt preload, and check of the measurement system) and load tests in liquid nitrogen. To simulate the expected lifetime of W7-X, several thousand load cycles were executed. Additionally, high load tests were performed to investigate the limits of the connection. shown that the connection could take the nominal loads with a safety margin of about 1.2. Above this the bolts starts to deform plastically. A MoS2 lubricant layer introduced between the relevant sliding surfaces of the bolted connection significantly reduced stick-slip which was detected during previous test campaigns. aper gives an overview on the functionality test and main conclusions of the experimental test campaign.