Nuclear fusion refers to a form of nuclear reaction in which atoms with small mass, mainly deuterium or tritium, polymerize with each other under certain conditions (such as ultra-high temperature and high pressure) to generate new nuclei with heavy mass, accompanied by huge energy release. There is huge energy in the nucleus, and the change of nucleus (from one nucleus to another) is often accompanied by the release of energy. If you change from a heavy nuclear to a light nuclear, it is called nuclear fission, such as an atomic bomb explosion; If a light nucleus becomes a heavy nucleus, it is called nuclear fusion, such as the energy source of the sun's light and heat. Compared with nuclear fission, nuclear fusion hardly brings environmental problems such as radioactive pollution, and its raw material can be directly taken from deuterium in seawater, and the source is almost inexhaustible, so it is an ideal energy source. At present, mankind has been able to achieve uncontrolled nuclear fusion, such as the explosion of hydrogen bombs. However, if energy can be effectively utilized by human beings, it is necessary to reasonably control the speed and scale of nuclear fusion to achieve sustained and stable energy output. Scientists are trying to study how to control nuclear fusion, but now it seems that there is still a long way to go. At present, there are several controlled nuclear fusion methods: ultrasonic nuclear fusion, laser confinement (inertial confinement) nuclear fusion, and magnetic confinement nuclear fusion (tokamak). The hydrogen bomb, a nuclear weapon more powerful than the atomic bomb, works by nuclear fusion. The process of nuclear fusion, contrary to nuclear fission, is a process in which several nuclei are aggregated into one nucleus. Only lighter nuclei can undergo nuclear fusion, such as hydrogen isotopes deuterium (dao) and tritium (chuan). Nuclear fusion can also release enormous energy, and it is more energy than nuclear fission. The process of hydrogen polymerization into helium continues inside the sun, and its light and heat are produced by nuclear fusion. Nuclear fusion can release enormous energy, but at present, people can only realize uncontrolled artificial nuclear fusion at the moment when the hydrogen bomb explodes. In order to use the huge energy produced by artificial nuclear fusion to serve mankind, it is necessary to make nuclear fusion under human control, which is controlled nuclear fusion. The realization of controlled nuclear fusion has an extremely attractive prospect. Not only because nuclear fusion can release huge energy, but also because deuterium, the isotope of hydrogen needed for nuclear fusion, can be extracted from seawater. After calculation, the energy released by extracting deuterium from 1 liter seawater for nuclear fusion is equivalent to the energy released by 100 liter gasoline combustion. The sea water in the world is almost inexhaustible, so the success of controlled nuclear fusion's research will help mankind get rid of the energy crisis. But at present, people can't carry out controlled nuclear fusion, mainly because the conditions required for nuclear fusion are very harsh. Nuclear fusion can only occur at a high temperature of 1 100 million degrees, so it is also called thermonuclear reaction. It is conceivable that no material can withstand the high temperature of 1 100 million degrees. In addition, there are still many unimaginable difficulties to overcome. Although there are many difficulties, people have made gratifying progress through continuous research. Scientists have designed many ingenious methods, such as using a strong magnetic field to constrain the reaction and using a powerful laser to heat atoms. It can be predicted that people will finally master the method of controlling nuclear fusion and make it serve mankind.