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I read that confined plasma in electromagnetic field uses in TOKAMAK nuclear fusion reaction. But I don't know what is the main role of plasma in fusion reaction. Is it use for producing energy required to fuse nuclei or something else?

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    $\begingroup$ The plasma is largely a consequence of giving the atoms/molecules enough energy that they start losing electrons. They need the high kinetic energy to overcome the Coulomb barrier produced by the protons of each nucleus in order to undergo fusion. So the plasma is unavoidable with current technology and in some cases is the primary constituent that the experimenters hope will undergo fusion. $\endgroup$ May 15, 2016 at 20:22

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You may have things a bit mixed up.

Plasma is not something that plays a role in fusion as if it were a tool or an instrument for its achievement. It is instead the only possible medium where nuclear fusion can occur: very basically, high enough temperature for protons to overcome the Coulomb repulsion, and high enough density for increased chances of fusion reactions.

So it is an intimate part of nuclear fusion, rather than an appendix or a component of it. All components of nuclear fusion rather revolve around the plasma: how to heat it, how to contain it, how to shape it, how to control it, etc.

Whether in nature or in laboratories, these questions are answered by ancillary structures (e.g. large gravitational and magnetic fields, vacuum vessels, magnets, neutral beam injectors, radio-frequency antennas, lasers or solenoids), but the plasma will always be the central and indispensable part of the whole process of producing energy through nuclear fusion.

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  • $\begingroup$ What is the application of quantum tunnelling in this process? Does quantum tunnelling is in now applicable technology for nuclear fusion reaction? $\endgroup$
    – Absaed
    May 17, 2016 at 6:15
  • $\begingroup$ quantum tunneling is what allows fusion to occur in the first place, but without high temperatures, the probability of fusion is extremely low $\endgroup$
    – ntno
    Sep 6, 2016 at 21:14
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At the temperatures required for fusion reactions, matter can only exist in the plasma state. That's rather inconvenient for designers of fusion reactors, since plasma is hard to control and contain.

And that's why the claims about cold-fusion were so appealing. Cold fusion promised to provide fusion power without the hassle of dealing with high temperature plasma. Unfortunately, those claims turned out to be false.

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  • $\begingroup$ But how tokamark gain power to fuse nucleus? $\endgroup$
    – Absaed
    May 15, 2016 at 18:39
  • $\begingroup$ The tokamak reactor never generated more power than it consumed. In other words, it was using power from the power grid (just like the light bulbs in your house) to heat the plasma. $\endgroup$ May 15, 2016 at 19:23
  • $\begingroup$ So,fusion occurs in the confined plasma? $\endgroup$
    – Absaed
    May 16, 2016 at 3:15
  • $\begingroup$ @Absaed Yes, the plasma contains deuterium ($^2H$) and tritium ($^3H$) nuclei that are the fuel for the reactor. $\endgroup$ May 16, 2016 at 4:22

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