Atoms are built out of three main particles: protons and neutrons—which make up the atomic nucleus—and electrons, the negatively charged particles that swarm around the nucleus and help atoms bond to one another to form molecules.Most of the energy we use, such as burning gasoline, comes from chemical reactions. These involve the electrons and breaking or making the chemical bonds they form.But the real juice is in the nucleus. These kinds of interactions, of atomic nuclei fusing together or splitting apart, are millions of times more potent than mere chemical reactions. In a nuclear reaction, a part of the mass of the neutron turns into energy, and the energies released are a million times those of mere chemical reactions. Chemical energy will move your car well enough. It is fusion energy that drives the stars.file not foundThe nuclear power that most of us are more familiar with is nuclear fission. The basic goal in fission is to take a heavy, unstable atom, like an isotope of uranium, and shoot a neutron at it. When the atom splits, energy is released, and the atomic fragments smash into other uranium atoms, releasing more energy and atomic fragments, and so on, creating a chain reaction.We are all familiar with the problems presented by fission power. Uranium fuel is a limited resource. The radioactive byproducts of fission have proven extremely difficult, and costly, to dispose of safely.Fusion is the process of forcing atomic nuclei together, rather than ripping them apart.Instead of working with big, heavy and unstable atoms like uranium and plutonium, fusion works much higher up on the periodic table. In fusion reactions, light elements with small nuclear masses like hydrogen and helium are forced together under conditions of extreme heat and pressure. The only byproducts of fusion are other light elements, like helium, and a tiny amount of radioactivity that quickly dissipates.Humans have managed to drive some rather impressive fusion reactions, if you consider the hydrogen bomb. But controlling fusion, and harnessing its power for peaceful means, has been much more difficult.The most venerable of fusion technologies, the tokamak, first was experimented with in the 1950s. In a tokamak, hydrogen gas is suspended inside a magnetic field and heated to 100-million-degree plasma. The other strong candidate is laser fusion. Hundreds of powerful lasers are aimed at a pellet of fuel, from all directions. The heat and pressure ignite the fuel, and the shockwave from that explosion travels inward toward an even smaller pellet of deuterium inside. Both approaches have gobbled up billions in research dollars. And while each have successfully driven fusion, both are decades away from actual energy production.