i are heated to very high temperatures (which is the same as saying they travel at very high speeds); therefore, the repulsive force won’t be able to prevent the collision. In addition, powerful magnetic fields force the nuclei into a small space to increase the chance of collision.
In the reaction, the two nuclei combine to form one nucleus. This has two protons, so it’s a helium nucleus. It also has two neutrons, making it a helium-4 nucleus (an alpha particle). The fifth neutron is ejected at very high speeds. Since it doesn’t carry a charge, it is not affected by the magnetic fields and escapes; an external collector can capture it and convert its energy to heat.
The large amount of energy released is due to a principle called binding energy. The strong force, the most powerful of the forces, holds the protons and neutrons together in the nucleus (if not, the positive protons would strongly repel each other). When the nuclear particles are combined in the nucleus, the mass of the nucleus is slightly less than the mass of the individual particles (this difference is called the mass defect), and the energy released by this is the binding energy. The mass of the helium-4 nucleus and the neutron is slightly less than the masses of the hydrogen-2 (deuterium) and hydrogen-3 (tritium): the difference is less than 2% of the mass of a proton or neutron. However, as Albert Einstein explained with his famous equation E=mc2, this tiny mass results in a lot of energy.
Perhaps after 4.6 billion years of using fusion-produced energy from the sun, Earth is ready to try it for itself.