Structural Analysis of Wendelstein 7-X Nonplanar Coil Type 1 in Self-Field Test Conditions

The Wendelstein 7-X (W7-X), the largest modular stellarator in the world, is in operation at Max Planck Institute for Plasma Physics in Greifswald, Germany. The magnet system of the W7-X consists of 50 nonplanar and 20 planar superconducting coils, which are supported by a massive central support structure. All superconducting coils have been subjected to gravity and electromagnetic force due to the interaction between self-field and the coil current in the test conditions in Saclay, France. Each coil is equipped with a few mechanical sensors. Some of the sensors have indicated considerable deviation from the numerical prediction. The nonplanar coil Type 1 is an example of such deviations. This technical note presents structural analyses performed to verify the numerical modeling by checking the stresses in the measurement points. In order to find the reason from the finite element model, three factors are considered: mesh refinement, increasing the region of mesh refinement, and changing the element supports. The results show that the three factors have no impact on the stresses at the measurement points. Finally, special attention has been paid to the sensors during commissioning of the W7-X, which revealed that lack of information about boundary conditions or temperature fluctuations could be the reason for the original discrepancies.