The Wendelstein 7-X (W7-X) reactor is an experimental stellarator (nuclear fusion reactor) built in Greifswald, Germany, by the Max Planck Institute of Plasma Physics (IPP), and completed in October 2015. Its purpose is to advance stellarator technology (first conceived by Lyman Spitzer) and though this experimental reactor will consume far more power than it generates, it is used to evaluate the main components of a future fusion power plant; it was developed based on the predecessor Wendelstein 7-AS experimental reactor.
As of 2015, the Wendelstein 7-X reactor was the largest stellarator device. It is planned, circa 2021, 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.
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 3×1020 particles per cubic metre, and a plasma temperature of 60–130 megakelvin (MK).
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 teslas.
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.
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 USD of the eventual 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 (which consumed more than 1 million assembly hours) 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 MK) for about 0.1 s on December 10, 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.
More than 300 discharges with helium were done in December and January with gradually increasing temperatures finally reaching six million degrees Celsius, to clean the vacuum vessel walls and test the plasma diagnostic systems. Then on February 3, 2016, operational phase 1 (OP-1) began, with production of the first hydrogen plasma to initiate the science program. The highest temperature plasmas were produced by four megawatt microwave heater pulses lasting one second: Plasma electron temperatures reached 100 MK, while ion temperatures reached 10 MK. More than 2,000 pulses were conducted before shutdown.
Such tests were planned to continue for about a month, followed by a scheduled shut-down to open the vacuum vessel and line it with protective carbon tiles and install a "divertor" for removing impurities and heat from the plasma. Then the science program will continue while gradually increasing discharge power and duration. The special magnetic field topology was confirmed in 2016.
Financial support for the project is about 80% from Germany and about 20% from the European Union. 90% of German funding comes from the federal government and 10% from the state government of 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-year 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 President of the Max Planck Society, Peter Gruss, announced that the United States would contribute 7.5 million dollars under the program "Innovative Approaches to Fusion" of the US Department of Energy.Technical University of Berlin (Germany)
University of Greifswald (Germany)
Forschungszentrum Jülich (Germany)
Karlsruhe Institute of Technology (Germany)
Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie (IGVP) at the University of Stuttgart (Germany)
Physikalisch-Technische Bundesanstalt (Germany)
Commissariat à l'énergie atomique et aux énergies alternatives (CEA; France)
Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT; Spain)
Institute of Nuclear Physics Kraków and National Centre for Nuclear Research (Poland)
Institute of Plasma Physics and Laser Microfusion, Warsaw (Poland)
KFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences (Hungary)
Trilateral Euregio Cluster (Germany/Belgium/Netherlands)
Los Alamos National Laboratory
Oak Ridge National Laboratory
Princeton Plasma Physics Laboratory
University of Wisconsin–Madison
Massachusetts Institute of Technology
National Institute for Fusion Science