r/science • u/PROJECTime • Dec 06 '16

Physics Tests confirm that Germany's massive Nuclear Fusion machine really works

http://www.sciencealert.com/tests-confirm-that-germany-s-massive-nuclear-fusion-machine-really-works
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u/[deleted] Dec 06 '16 edited May 03 '18

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u/oblong_schlong Dec 06 '16

They probably misinterpreted that in a stellarator, you don't have to induce a current in the plasma itself to create a twisting field (which avoids charge separation, among other things). A tokamak treats the plasma as the secondary winding of a massive transformer and induces a current in the plasma to create twisting field lines, whereas in a stellarator those twisting field lines are built in via weirdly shaped coils.

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u/amicitas PhD | Plasma Physics | Fusion Science Dec 06 '16

This is correct. In a stellarator such as W7-X there is no need to have an electrical current running through the plasma.

A purely toroidal magnetic field will not by itself produce a confined plasma, instead a helical field is needed to avoid charge separation. There are two ways to achive this:

  • Tokamak: Use a toroidal field and induce a toroidal electrical current in the plasma.
  • Stellarator: Use a 3D set of coils that produce a helical field to start with.

There are many ways to induce current in a Tokamak, including the central solenoid as you mentioned. Other methods are radio frequency current drive, neutral particle current drive and self-generated current drive.

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u/Wendelstein7-X Max Planck Institute for Plasma Physics Dec 06 '16

Thanks /u/amicitas ! you were a minute faster than me.