The Wendelstein 7-X (W7-X) experimental device is presently being built at the Max-Planck-Institute for Plasma Physics (IPP) in Greifswald, Germany.

The modularity of the machine is achieved using five identical modules which form a torus of 16 meters outer diameter. Each module consists of a plasma vessel, ten non-planar main field coils, four planar coils and an outer vessel sector with ports. To achieve steady-state operation, the coils are superconducting. Two different plasma heating systems, ECRH and NBI, are planned for the first operation phase of W7-X.

Module-based assembly is a new approach for large fusion machines. There are three main assembly steps of the core machine. First, half-modules are assembled from a plasma vessel section, five non-planar and two planar coils and related support structures. In the second step, two half-modules are connected to form a module. Then the five modules are connected, after which the outer vessel is closed.

The paper reports on about the latest progress in assembly, highlighting the most challenging tasks, describes future work leading to the start of W7-X commissioning in 2014.