Where/how does the heat extraction take place? Are they planning to put water pipes in the walls of the confinement unit? I'm struggling to understand because in the diagrams I see a powerful magnetic field containing the particles, and then a near vacuum. Those two things alone must make heat transfer very difficult, no? I don't see where the produced energy gets extracted.
Sure, but how? What physical processes are being used? Most of us can understand how hot fision encased in water turns to steam and runs a steam engine (even if the reality is still quite complex). But how does the thin-plasma get converted to steam?
Fast neutrons leaving the confinement field. Most of the energy goes into the blanket between the first wall of the vessel and the confinement coils. This blanket is made of Be and Li. Be to act as a neutron multiplier and Li to breed tritium. The Li fission is actually energetically favorable and is a significant percentage of the power output. It is also the source of tritium fusion fuel. The byproducts of these reactions are helium. Liquid lithium can also double as a coolant in an efficient (high temperature differential) thermal cycle.
The rest of the power gets dumped into the divertor. This is a pretty violent section of the hull that has an enormous power density slamming into it (in ITER it will be similar to an atmospheric re-entry vehicle). There are games to play here though and the strike points can be blown up in size.