Bolted coil support at the W7-X module interface

Abstract

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 ±23 mm and 1 deg. The joint is capable to cope with forces up to 1.3 MN and moments up to 0.2 MNm. 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.

Technical challenges in the construction of the steady-state stellarator Wendelstein 7-X

“…An aluminium dummy was produced first, then trial installation followed, and the fit was measured. With this geometry-correction the stainless steel "bridge" was finally fabricated and the coil transition part underwent a finite element (FE) structural analysis [28].…”

Experiences From the Assembly of the Magnet System for Wendelstein 7-X

“…Additional supports are stiffening the neighboring coils at this location. Of those, the two lateral supports, need a precise form-lock with the coil body ensuring a remaining gap of less than 50 µm before the connection is tightened [9]. For that, the wedge-shaped contact contour at every coil is laser scanned and their position is laser tracker measured.…”

Structural analysis of W7-X: From design to assembly and operation

“…The test program for the magnet system has been successfully completed by tests of EKagrip® friction enhancing foils for elements to be installed at the module separation interface [26].…”

“…[26]), the support of assembly processes, reliable prediction of the stellarator structural behaviour at the maximum design value of 3T, establishing limits for machine operation, and study of new plasma scenarios and operational regimes. A further task is structural simulation of fault scenarios with deduction of corresponding operation instructions.…”

“…The magnet system global FE model includes the coils and their support structure, the The results of the GM FE analyses are transferred to the local models in terms of forces and moments, in terms of displacements in case sub-modelling procedures are used, or the local component model is embedded in the GM [5][6][7][8][9]26].…”