The energy released in a fusion reaction could be captured and converted into electrical energy. The difficulty in creating a fusion reactor is confining the reactants, typically deuterium and tritium nuclei, at temperatures needed for fusion. There are two approaches: magnetic and inertial confinement. Most effort has gone into magnetic confinement where the positively charged nuclei are trapped in evacuated regions containing strong magnetic fields that keep the nuclei from colliding with the metallic walls of the equipment. The swarms of charged nuclei, a plasma, must then be raised to very high temperatures and held at that temperature long enough for fusion to take place. So there are three variables: number of nuclei, their energy (or temperature), and the confinement time. The product of these three variables determines whether or not fusion will occur.