Nuclear fusion, that is, when light nuclei (deuterium and tritium) combine into heavier nuclei (helium).

Thermalnuclear reaction [1], or the fusion reaction of atomic nuclei, is a promising new energy at present. Light nuclei involved in nuclear reactions, such as hydrogen (hydrogen), deuterium, tritium, lithium, etc., are fusion reactions caused by obtaining the necessary kinetic energy from thermal motion (see nuclear fusion). Thermalnuclear reaction is the basis of the explosion of a hydrogen bomb, which can generate a large amount of thermal energy in an instant, but it cannot be used at present. If the thermonuclear reaction can be produced and carried out within a certain constraint area and is controlled according to people's intentions, a controlled thermonuclear reaction can be achieved. This is a major issue currently underway for experimental research. Controlled thermonuclear reactions are the basis of fusion reactors. Once a fusion reactor is successful, it may provide humans with the cleanest and inexhaustible energy.

[Edit this paragraph] Definition

Nuclear fusion refers to a nuclear reaction form in which atoms with a smaller mass, mainly referring to deuterium or tritium. Under certain conditions (such as ultra-high temperature and high pressure), the nuclei are polymerized to each other, forming new heavier nuclei, and are accompanied by huge energy release. Atomic nuclei contains huge energy, and the change of atomic nuclei (changing from one nucleus to another) is often accompanied by the release of energy. If it changes from a heavy nucleus to a light nucleus, it is called nuclear fission, such as the explosion of an atomic bomb; if it changes from a light nucleus to a heavy nucleus, it is called nuclear fusion, such as the source of energy for the sun to emit light and heat.

Compared with nuclear fission, nuclear fusion will hardly bring about environmental problems such as radioactive pollution, and its raw materials can be directly taken from deuterium in seawater, with almost endless sources, which is an ideal energy method.

At present, humans can achieve uncontrolled nuclear fusion, such as the explosion of hydrogen bombs. However, in order for energy to be effectively utilized by humans, they must be able to reasonably control the speed and scale of nuclear fusion and achieve continuous and stable energy output. Scientists are working hard to study how to control nuclear fusion, but it seems that there is still a long way to go.

Currently, several main controllable nuclear fusion methods:

Ultrasonic nuclear fusion

Laser constraint (inertial constraint) nuclear fusion

Magnetic constrained nuclear fusion (Tokamak)

[Edit this section] Supplementary content

The energy released by each gram of deuterium fusion is 5.8×108kJ, which is greater than the energy released by each gram of uranium fission (8.2×107KJ). From the perspective of energy, nuclear fusion has several aspects superior to nuclear fission: First, the fusion product is a stable helium nucleus, without radioactive pollution, and no waste that is difficult to deal with; Second, the fusion raw material deuterium is relatively rich in resources, and the ratio of deuterium to hydrogen in seawater is 1.5×10-4:1, and the total amount of water in the earth's Shanghai is about 1,018 tons, which contains a large amount of deuterium, and refining deuterium is much easier than refining uranium. Unfortunately, this fusion reaction requires a very high temperature to overcome the two

The huge repulsion between positively charged deuterium nuclei (from theoretical calculations, it takes a high temperature of 109℃ to overcome this Coulomb repulsion). The principle of manufacturing a hydrogen bomb is to use a small atomic bomb as a detonation device to generate instantaneous high temperature to cause the above-mentioned fusion reaction to explode. Various fusion reactions can occur between several isotopes of hydrogen element. This change process exists between the universe, and the huge energy radiated from the sun comes from this type of nuclear fusion. But we have no way to use this type of nuclear fusion on the earth to generate electricity. How to achieve such a high temperature? What materials are used to make a reactor? How to control the fusion process and other questions are still unanswered.

Supplement: Latest news about China's nuclear fusion device:

Xinhuanet, Hefei, September 29 (Reporter Yu Fei, Cai Min and Cheng Shihua) EAST, the world's leading new generation of China's thermonuclear fusion device, successfully completed the discharge experiment for the first time on the 28th, obtaining a high-temperature plasma discharge of 200 kAh and a time of nearly 3 seconds.

Researcher Li Jiangang, director of the Institute of Plasma of the Chinese Academy of Sciences, who is responsible for this project, said in an interview with Xinhua News Agency that this experiment achieved physical experiments at various stages such as high temperature of 100 million degrees of the device, plasma establishment, and circular cross-section discharge, achieving the expected results.

Expert of the process appraisal team and researcher Jin Duo from the Basic Science Research Bureau of the Chinese Academy of Sciences announced at a press conference after the experiment that EAST has passed the national "Ninth Five-Year Plan" major scientific engineering process appraisal. Dr. Gary Jackson, general atomic energy company in the United States, said: "EAST has become the world's first fully superconducting non-circular cross-section nuclear fusion experimental device to be built and truly operated. It will maintain the world's advanced level in the next 10 years."

It is understood that the EAST device was independently designed and built by China for 8 years and cost 200 million yuan.

The reporter saw in the experimental control room that this large object, which is almost cylindrical, is made of special non-magnetic stainless steel, is about 12 meters high and is about 5 meters in diameter. It is reported that its total weight reaches 400 tons.

Researcher Li Jiangang said that compared with similar international experimental devices, EAST is an advanced nuclear fusion experimental device with the least funds, the fastest construction speed, the earliest to be put into operation, and the fastest plasma discharge after operation.

"This means that humans have made significant progress in the field of nuclear energy research and utilization, and also marks that China has entered an international advanced level in this field," said Li Jiangang.

People realize that thermonuclear fusion starts with the explosion of hydrogen bombs. When the hydrogen bomb explodes, it releases great energy, which brings disaster to mankind. However, scientists hope to invent a device that can effectively control the process of "hydrogen bomb explosion" and allow energy to be continuously and stably output to solve the energy shortage crisis facing mankind.

In the mid-1980s, the United States, France and other countries launched the 4.6 billion euro International Thermal Nuclear Experimental Reactor (ITER) program, aiming to build the world's first controlled thermonuclear fusion experimental reactor to deliver huge clean energy to humans. This process is similar to the process by which the sun generates energy, so the controlled thermonuclear fusion experimental device is also commonly known as the "artificial sun".

China joined the ITER program in 2003. The Institute of Plasma of the Chinese Academy of Sciences, located in Hefei, Anhui is the main domestic undertaking unit of this international science and technology cooperation program. The EAST device it researches and builds has a stable discharge capacity of 1,000 seconds, exceeding all similar devices in the world.

Professor Wan Xi, general manager of EAST University Science Engineering, said that compared with ITER, EAST is much smaller in scale, but both are fully superconducting non-circular cross-section tokamak, that is, the plasma position shape and main engineering and technical foundations of the two are similar, and EAST is at least 10 to 15 years earlier than ITER. Therefore, whether from the perspective of talent training and laying the engineering and physical foundations, EAST will make important and substantial contributions to the ITER plan, and thus make important contributions to human development and ultimately use of nuclear fusion energy.

However, researcher Wan Xi said that although the wonder of the "artificial sun" first appeared in the laboratory, it is still a long way from real commercial operation, and the electricity it emits cannot enter people's homes in a short period of time. However, he predicted that based on the current research status of countries around the world, this dream may be realized as soon as 30-50 years.

Wan Xi said that after the future steady-state thermal nuclear reactor is used for commercial operation, the energy generated by humans will be enough for hundreds of millions or even billions of years. In the long run, nuclear energy will be the main energy after oil, coal and natural gas, and humans will move from "oil civilization" to "nuclear energy civilization."

[Edit this section] Principle

Simple answer: According to Einstein's mass-energy equation E=mc2.

When the nucleus undergoes fusion, part of the mass is converted into energy and released.

As long as there is a trace of mass, it can be converted into a large amount of energy.

When two light nuclei collided, one nucleus could form and release energy. This is the fusion reaction, and the energy released in this reaction is called fusion energy. Fusion energy is another important way to utilize nuclear energy.

The most important fusion reactions are:

Where D is deuteronucleus (heavy hydrogen), T is triton (super heavy hydrogen). The total effect of the above two groups of reactions is:

That is, every 6 deuterated nuclei are burned out, a total of 43.24 MeV is released, which is equivalent to an average of 3.6 MeV per nuclei. It is 4 times higher than the average of 200/236=0.85 MeV per nuclei in the N+ fission reaction. Therefore, fusion energy is a nuclear energy that is more huge than fission energy.

The fuel used by nuclear fusion energy is deuterium (D) and tritium. Deuterium exists in large quantities in seawater. There is one deuterium atom in every 600 hydrogen atoms in seawater, and the total amount of deuterium in seawater is about 40 trillion tons. The fusion energy released by the complete fusion of deuterium contained in seawater is equivalent to the energy of 300 liters of gasoline fuel. According to the energy consumed by the world at present, the fusion energy of deuterium in seawater can be used for tens of billions of years. Tritium can be made of lithium. Lithium mainly contains two isotopes of lithium-6 and lithium-7. After lithium-6 absorbs a thermal neutron, it can become tritium and releases energy. Lithium-7 must absorb fast neutrons to become tritium. Although the reserves of lithium on the earth are much less than deuterium, there are more than 200 million tons. Using it to make tritium is enough to use the age when humans use deuterium and deuterium fusion. Therefore, nuclear fusion energy is an inexhaustible new energy.

In the foreseeable time for human survival on Earth, deuterium in water is enough to meet the energy needs of mankind in the next few billion years. In this sense, the fusion fuel on Earth is infinitely rich in meeting future needs. The development of fusion energy will solve human energy needs "once and for all". Over the past sixty years, scientists' unremitting efforts have shown a bright future for mankind in this regard.

A typical fusion reaction is

411H—→42He+20-1e+2.67×107eV

21H+21H—→32He+10n+3.2×106eV

21H+21H—→31H+11H+4×106eV

31H+21H—→42He+10n+1.76×107eV

The net reaction of the last three reactions is

521H—→42He+32He+11H+210n+2.48×107eV

That is, 2.48×107eV energy is released after every 5 21H fusions.

Deuterium is a very rich hydrogen isotope. There is 1 deuterium atom for every 6,500 hydrogen atoms in the ocean, which means that the ocean is the potential source of a very large amount of deuterium. There are 1.03×1,022 deuterium atoms in 1L seawater alone, which means that the potential energy of deuterium atoms in every 1Km3 seawater is equivalent to the energy of burning 1360 billion barrels of crude oil. This number is about the total oil reserves contained on the earth.

To make fusion between atomic nuclei, they must be brought close to the femtometer level. To reach this distance, the nuclei must have great kinetic energy to overcome the huge repulsion between charges. To make nuclei have sufficient kinetic energy, they must be heated to very high temperatures (more than a few million degrees Celsius). Therefore, nuclear fusion reaction is also called thermonuclear reaction. The high temperature generated by the explosion of atomic bombs can cause thermonuclear reactions, and this is how the hydrogen bomb explodes.

Controlled nuclear fusion is a controlled reaction of a large number of nuclear fusion at high temperatures, and at the same time releases energy. Deuterium is the most important fusion fuel, and the ocean is the potential source of deuterium. Once controlled nuclear fusion with deuterium as the basic fuel can be achieved, people will almost have inexhaustible energy. The large amount of fusion energy released by the hydrogen bomb explosion and the large amount of fission energy released by the atomic bomb explosion are uncontrollable. Just over ten years after the first atomic bomb exploded, people found a way to control the fission reaction and built a fission power station. It was originally thought that the hydrogen bomb could build a fusion power station after the explosion, but it was not so simple. Even the fusion reaction that could occur under the conditions of the earth:

31H+21H—→42He+10n+1.76×107eV
Chapter completed!