Wendelstein 7-X

Wendelstein 7-X

File:Wendelstein7-X Torushall-2011.jpg
Type	Stellarator
Major radius	5.5 m
Minor Radius	0.53 m
Plasma volume	30 m3
Magnetic field	3 T
Heating	14 MW
Location	Greifswald, Germany

Schema of the coil system (blue) and plasma (yellow). A magnetic field line is highlighted in green on the yellow plasma surface.

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Entrance of the Wendelstein 7-X research complex in Greifswald

Superconducting feed lines being attached to the superconducting planar coils.

File:W7-X Stellarator Experiment.jpg

Construction as of May 2012. Visible are the torus, offset in the test cell, and the large overhead crane. Note the workers for scale.

File:Interior of W7-X stellarator.jpg

Wide-angle view inside the W7-X stellarator (under construction), showing the stainless cover plates and the water-cooled copper backing plates (which will eventually be covered by graphite tiles) that are being installed as armor to protect against plasma/wall interactions.

The Wendelstein 7-X (W7-X) reactor is an experimental stellarator (nuclear fusion reactor) built in Greifswald, Germany, by the Max-Planck-Institut für Plasmaphysik (IPP), and completed in October 2015. It is a further development of Wendelstein 7-AS. The purpose of Wendelstein 7-X is to evaluate the main components of a future fusion reactor built using stellarator technology, even if Wendelstein 7-X itself is not an economical fusion power plant.

The Wendelstein 7-X reactor is the largest fusion device created using the stellarator concept which was the brainchild of physicist Lyman Spitzer. It is planned to operate with up to 30 minutes of continuous plasma discharge, demonstrating an essential feature of a future power plant: continuous operation.

The name of the project, referring to the mountain Wendelstein in Bavaria, was decided at the end of the 1950s, referencing the preceding project from Princeton University under the name Project Matterhorn.

The research facility is an independent partner project with the University of Greifswald.

Design and main components

The Wendelstein 7-X device is based on a five field-period Helias configuration. It is mainly a toroid, consisting of 50 non-planar and 20 planar superconducting magnetic coils, 3.5 m high, which induce a magnetic field that prevents the plasma from colliding with the reactor walls. The 50 non-planar coils are used for adjusting the magnetic field. It aims for a plasma density of 3 x 10²⁰ particles/cubic metre, and a plasma temperature of 60 - 130 million K.

The main components are the magnetic coils, cryostat, plasma vessel, divertor and heating systems.

The coils (NbTi in aluminium) are arranged around a heat insulating cladding with a diameter of 16 meters, called the cryostat. A cooling device produces enough liquid helium to cool down the magnets and their enclosure (about 425 metric tons of 'cold mass') to superconductivity temperature (4 K). The coils will carry 12.8 kA current and create a field of up to 3 Tesla.

The plasma vessel, built of 20 parts, is on the inside, adjusted to the complex shape of the magnetic field. It has 254 ports (holes) for plasma heating and observation diagnostics. The whole plant is built of five almost identical modules, which were assembled in the experiment hall.

The heating system includes 10 megawatts of microwaves for Electron Cyclotron Resonance Heating (ECRH), for up to 10 seconds, and can deliver 1 megawatt for 50 seconds during operational phase 1 (OP-1). For operational phase 2 (OP-2), after completion of the full armor/water-cooling, up to 8 megawatts of neutral beam injection will also be available for 10 seconds, while the microwave system will be extended to true steady state (30 minutes). An Ion Cyclotron Resonance Heating (ICRH) system will become available for physics operation in OP1.2.

A system of sensors and probes based on a variety of complementary technologies will measure key properties of the plasma, including the profiles of the electron density and of the electron and ion temperature, as well as the profiles of important plasma impurities and of the radial electric field resulting from electron and ion particle transport.

History

The German funding arrangement for the project was negotiated in 1994, establishing the Greifswald Branch Institute of the IPP in the north-eastern corner of the recently integrated East Germany. Its new building was completed in 2000. Construction of the stellarator was originally expected to reach completion in 2006. Assembly began in April 2005. Problems with the coils took about 3 years to fix. The schedule slipped into late 2015.

A three-lab American consortium (Princeton, Oak Ridge, and Los Alamos) became a partner in the project, paying 7.5 million Euros of the projected total cost of 1.06 billion Euros. In 2012, Princeton University and the Max Planck Society announced a new joint research center in plasma physics, to include research on W7-X.

The end of the construction phase was officially marked by an inauguration ceremony on 20 May 2014. After a period of vessel leak-checking, beginning in the summer of 2014, the cryostat was evacuated, and magnet testing was completed in July 2015.

The reactor successfully produced helium plasma (with temperatures of about 1×10⁶ K) for about 0.1 s on 10 December 2015. For this initial test with about 1 mg of helium gas injected into the evacuated plasma vessel, microwave heating was applied for a short 1.3 MW pulse. Initial tests with hydrogen plasma are planned for early 2016, and the operational phase 1 (OP-1) is expected in 2016.

Financing

Financial support for the project is about 80% from the host nation and about 20% from the European Union. The German funding is in the ratio 9:1 by the federal government and the Land Mecklenburg-Vorpommern. The total investment for the stellarator itself over 1997-2014 amounted to 370 million euros, while the total cost for the IPP site in Greifswald including investment plus operating costs (personnel and material resources) amounted to EUR 1.06 billion for that 18-years period. This exceeded the original budget estimate, mainly because the initial development phase was longer than expected, doubling the personnel costs.

In July 2011, the Max-Planck-Institut announced that the United States would contribute 7.5 million dollars under the program "Innovative Approaches to Fusion" of the US Department of Energy.

Collaborating institutes

Germany

• Technische Universität Berlin
• Universität Greifswald
• Forschungszentrum Jülich
• Karlsruher Institut für Technologie
• Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie der Universität Stuttgart
• Physikalisch-Technische Bundesanstalt

Europe

• Commissariat à l'énergie atomique et aux énergies alternatives (France)
• Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (Spain)
• INP Krakau und National Centre for Nuclear Physics (Poland)
• Institute of Plasma Physics and Laser Microfusion, Warschau (Poland)
• KFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences (Hungary)
• Trilateral Euregio Cluster (Germany/Belgium/Netherlands)

United States

• Los Alamos National Laboratory
• Oak Ridge National Laboratory
• Princeton Plasma Physics Laboratory
• University of Wisconsin–Madison

Japan

• National Institute for Fusion Science

See also

• Similar stellarators:
  • Large Helical Device, Japan, Heliotron, superconducting, 1998-
  • Helically Symmetric Experiment, USA, Quasi-Helically Symmetric
  • National Compact Stellarator Experiment, three field-period Helias configuration - Had similar coil problems - construction halted in 2008

External links

• Wendelstein 7-X – Max-Planck-Institut für Plasmaphysik