The plasma needs to be >=200 million kelvin, the superconductor that contains it doesn't work if its not <=20 kelvin. No wonder this is an engineering nightmare!
I wonder if gradients that extreme exist in nature.
I won't say it's not challenging, but bear in mind that while the plasma is at high temperature, it has very low density. The atoms are moving really fast but there aren't many of them. Consequently the amount of heat is comparable to fossil plants.
The magnets are on the outside of the containment vessel, their whole point is to keep the plasma in the center. What little leaks out ablates the walls of the container, it never even touches the magnets.
I wonder if gradients that extreme exist in nature.