Spacers and supports belong to the critical elements in the structure of a nuclear fusion device, particularly, when they are installed in the vacuum or superconducting magnet system of the reactor. Some of these supports have to sustain high loads while allowing a certain amount of tangential movement with low friction and without any stick-slip motion. Such movement is caused by mechanical and thermal strain during baking out of the vacuum vessel, cooling down, or energizing the superconducting magnets. Vacuum and cryogenic environments are extremely hostile for smooth sliding systems because conventional liquid lubricants cannot be employed and only a very limited number of materials for dry sliding systems under these conditions is available.
In order to test the friction behaviour of support elements between the field coils of the fusion experiment WENDELSTEIN 7-X which is currently under construction in Greifswald, Germany, a test rig was build at the Federal Institute for Materials Research and Testing (BAM) in Berlin, Germany. It allows testing in liquid helium environment at 4.2 K, with loads up to 150 kN, and a sliding velocity as low as 0.1 mm/s in reciprocating motion. First tests have shown that this device is appropriate for simulating the sliding behaviour or such support devices. The design and performance of the test rig are shown.
In earlier model tests the sliding behaviour of composite materials, MoS2- and carbon coatings were investigated in view of their suitability for WENDELSTEIN 7-X. Some results of these tests are also presented.
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