Not a stupid question at all. One could say the foundations of the entire ITER programme circle around need to answer that one. :) [0]<p>But on a more practical note: the containment for the plasma is a vacuum. All the matter inside the magnetic container is held within the plasma, and in simplified terms, between the &quot;surface&quot; of the plasma and the wall of the container there is _nothing_. Vacuum is a very good insulator, and the magnetic fields that control the plasma serve a dual purpose. Always, to prevent plasma from getting into contact with the walls of the container - but both to keep the energies within the ring, and to make sure any contact with the vessel can&#x27;t cool the plasma down.<p>The reason why vacuum is such a great insulator is easy to explain. Heat is transferred by conduction (contact), convection (heat exchangers), and radiation (ejected particles). When surrounded by vacuum, matter isn&#x27;t in contact with anything and heat transfer by conduction is 0. Because there is nothing for heat to flow to, also convection is effectively 0. Heat loss by radiation is far, far less than by conduction - and since plasma is a cloud of charged particles, 
even that is subject to the strong magnetic fields pushing the matter back.<p>0: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;ITER#Vacuum_vessel" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;ITER#Vacuum_vessel</a>