My question was inspired by this one - in particular the image it has (also shown here):

enter image description here

Why does the external casing of the Stellarator (in particular, the Wendelstein 7-X shown in the above image) have so many orifices, hinged/bolted panels, protuberances, etc.?

For the record, I'm not questioning the odd shape of the whole device (already answered here), but rather just the exterior casing.

I'm convinced that the outer shell of this device bears a resemblance to something between the engine room of a submarine and the surface of the Death Star. :-)

  • $\begingroup$ nuclear fusion equivalent of developer mode $\endgroup$
    – Aloha
    Commented May 30 at 16:54

1 Answer 1


The external casing belongs to the cryostat that maintains the superconducting magnets at 4 K. It has 254 ports to heat and diagnose the plasma. For heating with neutral beams, you need relatively large ports. For doppler backscattering diagnostics, waveguides with a few centimeters diameter carry coherent electromagnetic radiation into the plasma chamber. There are also many passive viewing ports to diagnose, e.g. the radiation loss coming from the plasma with bolometers or the Thomson scattering signal of electrons that tells us their temperature and density. Essentially, you want to squeeze as many ports in between the magnetic coils as is feasible to effectively heat the plasma and see how it behaves without sacrificing cryostat or magnet performance. There is a high surface density of ports because you want to minimize cryostat volume for better cooling efficiency.

  • 6
    $\begingroup$ Also it is a research system so will have as many ports as possible for monitoring, instruments and any future ideas $\endgroup$ Commented Nov 18, 2017 at 5:36
  • 2
    $\begingroup$ Currently operating fusion experiments use tons of ports for purposes like those described above. Some of them are so old that adding something new requires removing a different system. So, even the huge number of ports shown for W7X isn't necessarily enough. $\endgroup$
    – EL_DON
    Commented Jul 5, 2018 at 18:46

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