The vessel is in a shape of the magnetic fields driven by a core. These magnetic fields keep the plasma contained in a ball of “fire” which does not touch the container which remains insulated by a vacuum, I believe.
It mentions something about an intense magnetic field that prevents the plasma from touching the sides of the containment vessel.
“So how does it not melt vaporize its containment vessel and everything around it?”
The containment vessel is magnetic fields. So the hydrogen reacting doesn’t touch anything that melts.
The key statistic that they DON’T give is how much energy went in and how much came out. It takes a lot of energy to run a Tokamak.
I’m not sure how they address your melting problem when they want to get the energy out in a useful form.