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I was reading about tokamaks, for usage in fusion, and it seems that the positive ions circle in one way in the toakmak, while the negative circles in another. That would make a lot of sense, as it would explain how the two of them are attracted by the center, even having opposite charges (using Lorentz laws, the negative charge would 'cancel' with the opposite velocity, and the force would be the same). That would also explain why you can't use a simple electrical field to keep the plasma still in a sphere (you would only be able to keep the positive part or the negative, not both). Is this correct? And if it is, then what makes the plasma move that way? There seem to be no explanation about that anywhere.

Since a toroidal field is curved and decreases in strength moving away from the axis of rotation, the ions and the electrons move parallel to the axis, but in opposite directions.

From Wikipedia

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Maybe this can help? – anna v Nov 24 '13 at 12:38
It is an interesting article. I think I got now. The electrial current itself is what moves the negative and positive particles in opposite directions... And the magnetic field then attracts them to the center. – Luan Nico Nov 25 '13 at 12:48

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