Recent results of the cold tests performed on the stellarator W7-X coils

The plasma fusion experiment Wendelstein 7-X (W7-X) will use a system of superconducting coils for the production of the magnetic field. In the first paragraph, W7-X is described briefly, with emphasis on the coil system. All the superconducting coils are tested thoroughly in a cryogenic test facility. The test program is described in the second paragraph. In the third paragraph, some test results are described in more detail. Focus is here on the measurement of mechanical stresses during cool-down and application of the electrical current to the coils. The measurement of the electrical impedance, performed in order to detect short-circuits, will also be described. Finally, we present the quench tests, which are used to investigate the superconductor quality, and the Paschen-tests used for the check of the electrical insulation.