There's a whole bunch of mechanisms, largely depending on the fusion architecture and the atoms being fused. For tokamak reactors the circular nature lends itself well to what you describe, though usually it's energy being imparted into the ions to keep them contained and away from the walls. In the 'standard' deuterium-tritium fusion model (the easiest to perform) fusion produces a helium nucleus and a neutron, where the neutron gets most of the energy. Since a neutron can't be contained by magnets it impacts the chamber walls. This heat is wicked away by, you guessed it, cooling water which turns into steam. In order to use a direct energy conversion strategy you need a fusion reaction that produces no neutrons, but we're not there yet.