JET is an experimental tokamak in which an extremely hot gas, the plasma, is confined by strong magnetic fields in a torus – a doughnut-shaped chamber. The fusion processes take place inside the doughnut – in the so-called plasma core, and the heat of this extremely hot gas needs to be well confined and isolated from the vessel wall inside which it is placed.

To maintain the plasma, one must make sure that

  • the vessel wall is protected from the hot plasma to avoid melting the wall
  • the plasma is well insulated from the wall to minimise heat loss
  • lost plasma energy is compensated by additional heating
  • harmful plasma instabilities are mitigated
  • the interaction between plasma and vessel wall does not harm the plasma performance