The Fusion Reactor is exactly the opposite of a Fission Reactor. Instead of splitting atoms to unlock energy, it fuses atoms together to form heavier ones, releasing energy in the process.
To start the Fusion Reactor, one must provide 50 Kilowatts into the reactor itself. Once the reaction is initiated, the fusion process commences as plasma is produced adjacent to the fusion core (one block away from it). While fusing, the atoms create a massive amount of heat that is transferred by electromagnets. This heat will be transferred into the surrounding water if it is provided. The water soon becomes hot enough to boil into steam, which can be used by Electric Turbines to generate electricity.
Fusion reactors can be extremely dangerous if not set up properly. If the plasma were to escape into the air, it would incinerate anything it touches. The plasma must be contained inside a combination of Electromagnets or Electromagnet Glass to prevent it from getting out and setting fire to your world.
The electromagnets and electromagnet Glass can be used interchangeably, but it is advisable to use Electromagnet Glass only as a viewing window. It is possible for two reactors to share part of the outer Electromagnet shell, saving the player some resources.
By placing a powered manipulator (from Resonant Induction) adjacent to the Reactor, it is possible to automatically insert Deuterium into it. This allows for the Fusion Reactor to be entirely automated with the appropriate set-up.