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Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Department of Energy.
Published by Fusion Energy Division, Oak Ridge National Laboratory
Building 5700 P.O. Box 2008 Oak Ridge, TN 37831-6169, USA
Editor: James A. Rome Issue 128 October 2010
E-Mail: jar@ornl.gov Phone (865) 482-5643
On the Web at http://www.ornl.gov/sci/fed/stelnews
Wendelstein 7-X Update
Wendelstein 7-X (W7-X) is a superconducting modular
stellarator that is under construction at the Max-Planck-
Institut für Plasmaphysik in Greifswald, Germany. These
items are taken from issue 5 of the Wendelstein 7-X newsletter
(September 2010).
Status
Two modules are already in their final position on the
machine base in the Torus Hall (Fig. 1). A third module
was transfered there in August. Soon this module, too, will
undergo final positioning. Work on the first module is concentrating
on the difficult installation of about 50 ports.
The ports provide access for the heating and diagnostics
systems required for scientific measurements, and for
cooling of in -vessel components.
A number of work packages have been completed in
recent weeks. Assembly of half-modules, where the coils
were threaded onto the plasma vessel, has been completed.
This workstation has been freed up for prepare the ports
for assembly. Two further extremely challenging work
packages were completed: all of the special coil slide bearings
have been manufactured, and the serial production of
helium piping is complete. Both required innovation and
expertise to employ novel manufacturing techniques.
Bus bar systems for Wendelstein 7-X completed
At the heart of W7-X are 70 superconducting coils, which
generate the stellarator’s magnetic field. At the end of
June, the team at the Forschungszentrum Jülich celebrated
the successful development and construction of the bus bar
system for Wendelstein 7-X. This milestone ensures that
the magnetic field coils can be supplied with high currents.
The bus bar system provides electrical connections
between the coils and to external power supplies. Ten coils
of each type are connected in series and then to one current
lead. The production was extremely complex, due to the
three-dimensional design of the bus bars and the large
forces that they must withstand. Components in the stellarator
will move as much as a few centimetres and the bus
bars have to absorb these streses. Furthermore, the bus
bars are installed in cramped space. This all results in
extremely high accuracy requirements for the design and
assembly.
Fig. 1. Two modules of W7-X on the machine base in the
Torus Hall.
In this issue . . .
Wendelstein 7-X update
Two sectors are now in place, and the bus bar system
is completed and installed. ..................................... 1
Stellarator News -2- October 2010
The bus bars (Fig. 2) are made from copper-niobium-titanium,
the same material as the coils. Specially woven
wires are placed in an aluminium jacket. Liquid helium
will flow through the jacket to cool the wires down to 4 K
(–269°C). Since the coils are designed to be switched off
very quickly, the electrical insulation was tested to
13000 V. Such a high level of performance is achieved by
using two layers of Kapton foil embedded in a fibreglass
reinforced epoxy resin. On the surface, a conductive lacquer
prevents buildup of static charge and helps to detect
short circuits.
The comprehensive expertise and specialized equipment at
the Forschungszentrum Jülich were utilized for the bus bar
manufacture. A computer-controlled manufacturing line
was specially built for the machining and bending of bus
bars.
After the first bus bars were produced, they were checked
on a 1:1 mock-up of a Wendelstein 7-X module. The first
bus bars were installed on a real module in 2009 while the
rest were still in production. Currently, four of the five
modules are equipped with their bus systems, and preparation
for the last module is in progress. In total, the Forschungszentrum
Jülich has produced and delivered 140
bus bars up to 14 m long. In addition, 400 brackets and
700 clamps have been made to attach the bus bars to the
modules, and 240 joints to connect the modules to the
coils. Some of the pieces of bus bar and clamps are shown
in Fig. 3.
After the bus bars were bent to shape with millimeter
accuracy, special transport racks were used to deliver them
to Greifswald to prevent any in-transit distortion. Prior to
assembly the ends were cut and bent precisely, transition
pieces were welded on, the ends were insulated electrically,
and detector wires were mounted. For the final
assembly the technicians used a technique learned from
Jülich production: in Fig. 4, the bus bars hang from helium
balloons as they are positioned delicately and precisely on
the modules.
Fig. 2. Preparation of the bus bars for assembly.
Fig. 3. Details of the bus bar assembly.
Stellarator News -3- October 2010
Andreas Dinklage
Max-Planck-Institut für Plasmaphysik Greifswald
Association Euratom-IPP
Wendelsteinstraße 1
Greifswald 17491, Germany
Phone: +49 3834 882328
E-mail: w7xnewsletter@ipp.mpg.de
Fig. 4. Assembly of the bus bars using helium balloons to
hold them suspended in air.