On March 24th, Professor Thomas Klinger, scientifi c director of Wendelstein 7-X, announced the completion of an important project milestone: The last coil had been threaded onto the plasma vessel. The Fusion News team was fortunate to have visited the site the week before. Here is a personal account from what can only be described as an impressive construction site.

The scene is a Wednesday morning in the assembly hall of the Wendelstein 7-X (W7-X) project at IPP Greifswald: While the visitors are still overwhelmed by the sheer size and complexity of the construction site, a camera team is busy setting up its equipment to produce 3Dfootage of the installation of one of the last coils onto the plasma vessel. Finally the star of the fi lm – a strangely shaped non-planar superconducting coil – is lifted up by the crane, turned around, given one last clean and hoisted over to the other side of the hall. One can virtually feel the quiet routine of the workers pervading through the room as they thread the 3.5 metre high and six ton heavy coil onto the plasma vessel with, in some places, mere millimetres to spare. Next door in the torus hall, the fi rst of fi ve modules that make up the entire plasma torus has already been given the outer steel shell with as many holes as a piece of Swiss cheese. The magnets and inner vessel have vanished inside the steel shell and, after all of the ports have been fi xed to the holes, the device will look like a huge, ringshaped object with innumerable legs sticking out in all directions. Dr. Wegener, who oversees the entire assembly, outlines the complexity of the construction: The machine weighs 725 tons, has a diameter of 16 metres and features 254 ports. Each of its fi ve modules contains 1000 main components. When the device is fi nally commissioned in mid 2014, around 700,000 man hours will have gone into the construction project. The first plasma is expected to be generated in 2015.

Large copper mirrors guide the ECRH system’s powerful microwaves through free air (Photo: Anja Richter Ullmann, IPP)

The next day we find ourselves in a long hallway which serves as a wavechannel for the electron cyclotron resonant heating (ECRH) system’s microwaves: What is a familiar sight from optical benches, i.e. mirrors sending light along certain paths, occurs here at a considerably larger scale. Copper mirrors and polarisers combine ten microwave beams, each with one megawatt of power and around 10 cm in diameter, into two large beams and send them into the plasma vessel. The ECRH system benefits from the new site, as the buildings could be adapted to suit to its needs, whereas most fusion experiments are restricted in space and need to make use of less effective waveguides rather than sending the microwaves through free air. ECRH is intended to be used as the main heating system for Wendelstein 7-X, just like at ITER. Hence the Greifswald team also conducts tests and experiments for ITER. It is currently testing a fast beam switch that ITER will need to prevent the formation of instabilities.

Further information can be found in the latest W7-X Newsletter:


Learning from Wendelstein 7-X

On March 17th and 18th, the JT-60SA and W7-X teams met in Greifswald to exchange ideas and hear about the lessons learned during Wendelstein’s construction phase. Nine of the thirteen visitors came from the JT-60SA group in Garching, while four came from Japan. Dr. Manfred Wanner, Seconded National Expert of IPP at the JT-60SA team and responsible officer for cryogenics, had been working in the W7-X project from 1996 until end of 2007. He initiated the meeting with the intention to support the young JT-60SA team to learn from the experiences gathered from the W7-X. Dr. Rem Haange, technical director at W7- X, chaired the sessions of the event. The timing was well chosen, as one of the last coils was being installed on W7-X, thus giving the JT-60SA team a chance to still see all stages of the assembly processes. At the meeting, the W7-X team provided a deep insight into their experiences with the organisation and management of such a complex scientific project, focussing, on lessons learned during the design, construction as well as testing and assembly of the superconducting coils. The team also touched on the overall assembly process, providing first hand information on issues such as special vacuum techniques and metrology. Furthermore, it provided detailed information on the organisation of the assembly process, including documentation, quality management and processing orders for main components, and problems that had to be solved, such as the practical handling of tolerances or suitable welding techniques. Other topics of the meeting included the construction of the supply systems such as the helium refrigeration plant and the power supplies for the superconducting coils. The JT- 60SA team was very grateful for the open and fruitful discussion that has helped to establish valuable contacts between both teams and uncovered interesting aspects that are of interest to both projects and that will be discussed subsequent to this meeting. Thanks to Manfred Wanner for his input