Wendelstein 7-X

The Wendelstein 7-X (abbreviated W7-X) reactor is an experimental stellarator built in Greifswald, Germany, by the Max Planck Institute for Plasma Physics (IPP), and completed in October 2015.[1][2] Its purpose is to advance stellarator technology: though this experimental reactor will not produce electricity, 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.

Wendelstein 7-X
Wendelstein7-X Torushall-2011.jpg
W7-X in 2011
Device typeStellarator
LocationGreifswald, Germany
AffiliationMax Planck Institute for Plasma Physics
Technical specifications
Major radius5.5 m (18 ft)
Minor radius0.53 m (1 ft 9 in)
Plasma volume30 m3
Magnetic field3 T (30,000 G)
Heating power14 MW
Plasma temperature(60–130)×106 K
Year(s) of operation2015–present
Preceded byWendelstein 7-AS
Schema of the coil system (blue) and plasma (yellow). A magnetic field line is highlighted in green on the yellow plasma surface.
Entrance of the Wendelstein 7-X research complex in Greifswald
Superconducting feed lines being attached to the superconducting planar coils
Construction as of May 2012. Visible are the torus, offset in the test cell, and the large overhead crane. Note the workers for scale.
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.

As of 2015, the Wendelstein 7-X reactor is the largest stellarator device. It has been anticipated to achieve operations of up to approximately 30 minutes of continuous plasma discharge in 2021, thus demonstrating an essential feature of a future fusion 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.[3]

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

Design and main componentsEdit

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 megakelvins (MK).[1]

The main components are the magnetic coils, cryostat, plasma vessel, divertor and heating systems.[4]

The coils (NbTi in aluminium[4]) are arranged around a heat insulating cladding with a diameter of 16 metres, 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[5]). The coils will carry 12.8 kA current and create a field of up to 3 teslas.[5]

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 nearly identical modules, which were assembled in the experiment hall.[4]

The heating system[6] includes 10 megawatts of microwaves for electron cyclotron resonance heating (ECRH), which can operate continuously and can deliver 80 MJ in the operation phase 1.2.[7] 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.[8] An ion cyclotron resonance heating (ICRH) system will become available for physics operation in OP1.2.[9]

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.[10]


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.[4] The schedule slipped into late 2015.[4][11][12]

A three-laboratory American consortium (Princeton, Oak Ridge, and Los Alamos) became a partner in the project, paying €6.8 million of the eventual total cost of €1.06 billion.[13] In 2012, Princeton University and the Max Planck Society announced a new joint research center in plasma physics,[14] to include research on W7-X.

The end of the construction phase, which required more than 1 million assembly hours,[15] was officially marked by an inauguration ceremony on 20 May 2014.[16] 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.[5]

Operational phase 1 (OP1.1) began 10 December 2015.[17] On that day the reactor successfully produced helium plasma (with temperatures of about 1 MK) for about 0.1 s. 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.[18]

The aim for the OP 1.1 was to conduct integrated testing of the most important systems as quickly as possible and to gain first experience with the physics of the machine.[17]

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 3 February 2016, production of the first hydrogen plasma initiated 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.[19]

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. The science program continued while gradually increasing discharge power and duration.[20] The special magnetic field topology was confirmed in 2016.[21][22]

Operational phase 1 (OP1.1) concluded 10 March 2016[17] and an upgrade phase began.

Operational phase 1 continued (OP1.2) in 2017[23] to test the (uncooled) divertor.

Wendelstein 7-X during OP1.2b

Operational phase 2 (OP2) is planned for the end of 2021 to test the cooled divertor.[24] Due to COVID-19, the upgrade has been somewhat slowed/delayed; plasma experiments are expected to resume no earlier than 2022.[25]

In June 2018 a record ion temperature of about 40 million degrees, a density of 0.8 × 1020 particles/m3, and a confinement time of 0.2 second yielded a record fusion product of 6 × 1026 degree-seconds per cubic metre.[26]

During the last experiments of 2018, the density reached 2 × 1020 particles/m3 at a temperature of 20 million degrees. With good plasma values, long-lasting plasmas with long discharge times of 100 seconds were obtained. Energy content exceeded 1 megajoule.[27][28]


Date Event
1980 Planning initiated[29][30]
1994 Project initiated
2005 Assembly began
2014 Inaugurated
December 2015 Begin operational phase OP1.1
2015 Successful helium plasma test at 1 MK for ~0.1 s
2016 Hydrogen plasma at 80 MK for 0.25 s
March 2016 End OP1.1, begin upgrade phase
June 2017 Begin operational phase OP1.2
June 2018 Fusion triple product of 6 × 1026 degree-second/m3[31]
November 2018 End OP1.2, begin upgrade phase
~2022[25] (planned) OP2 (steady-state operation)


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, while the total cost for the IPP site in Greifswald including investment plus operating costs (personnel and material resources) amounted to €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.[32]

In July 2011, the President of the Max Planck Society, Peter Gruss, announced that the United States would contribute $7.5 million under the program "Innovative Approaches to Fusion" of the United States Department of Energy.[33]

Collaborating institutesEdit

European UnionEdit

United StatesEdit


See alsoEdit


  1. ^ a b Introduction – the Wendelstein 7-X stellarator Retrieved 5 November 2014.
  2. ^ Clery, Daniel (21 October 2015). "The bizarre reactor that might save nuclear fusion". sciencemag.org. Science Magazine. Retrieved 25 October 2015.
  3. ^ WI-A, WI-B, WII-A, WII-B, W7-A: G. Grieger; H. Renner; H. Wobig (1985), "Wendelstein stellarators", Nuclear Fusion (in German), 25 (9), p. 1231, doi:10.1088/0029-5515/25/9/040
  4. ^ a b c d e Klinger, Thomas (14 April 2011). "Stellarators difficult to build? The construction of Wendelstein 7-X" (PDF). Retrieved 13 June 2011. 53 slides - many photos
  5. ^ a b c "Magnet tests on Wendelstein 7-X successfully completed". 7 July 2015. Archived from the original on 16 July 2015.
  6. ^ "Stellarator Heating and Optimization". Retrieved 10 December 2015.
  7. ^ "Microwave heating – ECRH". Retrieved 10 December 2015.
  8. ^ "Neutral Beam Injection Heating (NBI)". Retrieved 10 December 2015.
  9. ^ "Ion Cyclotron Resonance Heating (ICRH)". Retrieved 10 December 2015.
  10. ^ "Profile Diagnostics". Retrieved 10 December 2015.
  11. ^ Arnoux, Robert (15 April 2011). "The stellarator renaissance". Retrieved 13 June 2011.
  12. ^ Jeffrey, Colin (25 October 2015). "Wendelstein 7-x stellarator puts new twist on nuclear fusion power". www.gizmag.com. Retrieved 27 October 2015.
  13. ^ "US narrows fusion research focus, joins German stellarator". 1 September 2011.[permanent dead link]
  14. ^ "Princeton, Max Planck Society launch new research center plasma physics". 29 March 2012.
  15. ^ "Start of scientific experimentation at the Wendelstein 7-X fusion device". phys.org. 7 June 2016. Retrieved 11 October 2016.
  16. ^ Milch, Isabella (12 May 2014). "Preparations for operation of Wendelstein 7-X starting". Retrieved 16 May 2014.
  17. ^ a b c "Wendelstein 7-X Newsletter No. 13 / April 2017" (PDF).
  18. ^ "The first plasma: the Wendelstein 7-X fusion device is now in operation". Max Planck Institute for Plasma Physics. 10 December 2015. Retrieved 10 December 2015.
  19. ^ "Wendelstein 7-X: Upgrading after successful first round of experiments". phys.org. 11 July 2016. Retrieved 11 October 2016.
  20. ^ "Wendelstein 7-X fusion device produces its first hydrogen plasma". Max Planck Institute for Plasma Physics. 3 February 2016. Retrieved 4 February 2016.
  21. ^ Pedersen, T. Sunn; Otte, M.; Lazerson, S.; Helander, P.; Bozhenkov, S.; Biedermann, C.; Klinger, T.; Wolf, R. C.; Bosch, H. -S.; Abramovic, Ivana; Äkäslompolo, Simppa; Aleynikov, Pavel; Aleynikova, Ksenia; Ali, Adnan; Alonso, Arturo; Anda, Gabor; Andreeva, Tamara; Ascasibar, Enrique; Baldzuhn, Jürgen; Banduch, Martin; Barbui, Tullio; Beidler, Craig; Benndorf, Andree; Beurskens, Marc; Biel, Wolfgang; Birus, Dietrich; Blackwell, Boyd; Blanco, Emilio; Blatzheim, Marko; et al. (2016). "Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000". Nature Communications. 7: 13493. Bibcode:2016NatCo...713493P. doi:10.1038/ncomms13493. PMC 5141350. PMID 27901043.
  22. ^ "Tests confirm that Germany's massive nuclear fusion machine really works". ScienceAlert. Retrieved 7 December 2016.
  23. ^ "Wendelstein 7-X: Second round of experimentation has begun".
  24. ^ Milch, Isabella (16 March 2020). "Wendelstein 7-X fusion device at Greifswald to be upgraded". Retrieved 17 April 2020.
  25. ^ a b "Wendelstein 7-X Newsletter Nr. 16 / Juli 2020" (PDF). July 2020. Retrieved 4 September 2020.
  26. ^ "Wendelstein 7-X achieves world record for fusion product" Phys.org, 25 June 2018
  27. ^ "Successful second round of experiments with Wendelstein 7-X". www.ipp.mpg.de. Retrieved 22 March 2019.
  28. ^ Lavars, Nick (26 November 2018). "Wendelstein 7-X fusion reactor keeps its cool en route to record-breaking results". newatlas.com. Retrieved 1 December 2018.
  29. ^ "Milestones". www.ipp.mpg.de.
  30. ^ Grieger, G.; Renner, H.; Wobig, H. (1985). "Wendelstein stellarators". Nuclear Fusion. 25 (9): 1231–1242. doi:10.1088/0029-5515/25/9/040. ISSN 0029-5515.
  31. ^ "Wendelstein 7-X achieves world record". www.ipp.mpg.de. Retrieved 30 June 2018.
  32. ^ FAZ: Start frei für deutschen Sonnenofen vom 20. Mai 2014
  33. ^ Isabella Milch (7 July 2011). "USA joining the Wendelstein 7-X fusion project". Max Planck Institute of Plasma Physics. Retrieved 4 February 2016.

External linksEdit

Coordinates: 54°04′23″N 13°25′26″E / 54.073°N 13.424°E / 54.073; 13.424