The paper presents an overview of the design, finite element (FE) analysis results, tests, and assembly strategy of the bolted connection between the coils of neighboring W7-X modules. The design is based on an accurately machined bridge and allows the accommodation of expected misalignments of the coil positions up to ±23mm and 1°. The joint is capable to cope with forces up to 1.3MN and moments up to 0.2MNm. Loads are transmitted by a combination of form lock provided by tapered coil block shoulders, and by friction on the bottom of the blocks. Special friction-enhancing foils are inserted between the bridge bottom surfaces and coil blocks to ensure a friction factor above 0.5. Non-linear FE analyses with elastic–plastic material models show that local plastification and even slippage in spite of the initial high friction are unavoidable but stay within an acceptable margin. In parallel, machining and assembly tests have been carried out to check and simplify the design further, and to develop the manufacturing strategy.

The Wendelstein 7-X stellarator is presently under construction at the Max-Planck-Institute for Plasma Physics in Greifswald with the goal to verify that a stellarator magnetic confinement concept is a viable option for a fusion power plant. The superconducting magnet system has to fulfill demanding requirements regarding magnetic field, loads, manufacturing and assembly. The magnet support system consists of several types of structural components. The main one is the central support structure (CSS) to which the superconducting coils are connected through Central Support Elements (CSE). These are bolted interfaces that allow for flange opening to reduce loads on the components. The non-planar coils (NPC) are toroidially interconnected via lateral support elements (LSE) and narrow support elements (NSE). NSE are contact supports consisting of Al bronze pads that allow for sliding under large compressive loads between the coils. The planar coils (PC) are connected to the NPC through planar support elements (PSE). At the module and half-module separation planes Contact Elements (CTE) connect the neighbouring NPC. An integrated programme of design, FE analysis, experiments and assembly trials has been undertaken. The NSE experimental program provided confidence that the pads can cope with the requirements regarding loads and cycles. Weld trials provided procedures for installing the LSE whilst keeping shrinkage and distortion within tight limits. Tests have been carried out to provide insight on the functioning of the CSE, in particular of the bolts and high performance Superbolt reg -nuts during pre-load. This paper gives an overview of the integrated program on the W7-X support elements.

The Wendelstein 7-X (W7-X) superconducting coils will be subjected to high electro-magnetic forces and moments during the stellarator operation. It is therefore essential to prove that the mechanical connections which keep the coils joined together and linked to the magnet system Central Support Structure (CSS) are capable to take the operational loads during the machine lifetime.Critical connections identified by the finite element (FE) analysis of the magnet system are the bolted Central Support Elements (CSE) between coils and CSS. The most critical one, called NPC1Z1, was studied by using mock-ups. The tests were carried out at 77 K and consisted in applying the forces starting from zero and ramping them up to a given set point, so simulating the coils' energization, and back to zero. The loading steps were repeated for more than 3600 cycles in order to reproduce the W7-X lifetime, including the high load cycles, where the reference loads were exceeded with the aim to explore the limit of such bolted connection. The tests showed that the mock-ups could take the nominal loads, but at 120% of such loads plastic failure on the mock-ups occurred.This paper presents an overview of the design and assembly of the CSE, the test mock-ups and test device, the execution of the test as well as the results and main conclusions of the experimental campaign. (C) 2007 Elsevier B.V. All rights reserved.

The Wendelstein 7-X stellarator is presently under construction and assembly in Greifswald, Germany. Its ultimate goal is to verify that such stellarator magnetic confinement concept is a viable option for a demonstration fusion power-plant. The superconducting magnet system, capable to generate a average magnetic field up to 3 Tesla at the magnetic axis, is basically composed of non-planar and planar coils, and of a central support structure to which they are connected. This system is a complex mechanical structure which has to fulfil demanding requirements in terms of accuracy of the magnetic field, capability to take the operational loads, suitability of the manufacturing tolerances and assembly scheme, interfaces. The magnet system is interconnected by support elements which have been conceived and designed in such a way to react to the loads in a "balanced way", while complying with the other requirements mentioned above. Given the unprecedented complexity of such mechanical scheme, an integrated programme of design, FE analyses, tests, assembly trials has been undertaken. This paper gives an overview of the way this structure is conceived, of its key support elements, and of the results of the analyses and tests carried out so far