Thermonuclear

Thermonuclear refers to the energy released by the thermonuclear reaction.

Thermonuclear weapon, nuclear bomb involving thermonuclear energy. (The power of thermonuclear weapons is expressed in megatons.) Also called hydrogen weapon or H weapon.

Thermonuclear reaction, nuclear reaction of fusion of the nuclei of light atoms brought to a very high temperature.

Nuclear fusion

Nuclear (or thermonuclear) fusion is a nuclear reaction in which two atomic nuclei come together to form a heavier nucleus.

B-61 thermonuclear weapon. In the back it is assembled, in the middle it is divided into its major subcomponents, in the front it is almost completely disassembled. US government DOD and/or DOE, Public domain, via Wikimedia Commons

Fusion Energy (Thermonuclear Fusion)

The principle of thermonuclear fusion is the creation of a large nucleus from two lighter ones in a particular temperature (and therefore pressure) range. Artificial fusion therefore comes into play. This is undoubtedly the simplest fusion to achieve. It involves colliding a deuterium atom with the symbol 2H with a tritium atom with the symbol 3H (these are both isotopes of hydrogen).

The fusion of these two isotopes is advantageous because it produces a large amount of energy. Indeed the fusion of two very light nuclei at the start produces more energy than the fusion of two larger nuclei such as iron for example. It is also easier to make.

At this level a physical problem arises. The nuclei are both positively charged and we know that, according to Coulomb’s law, identical charges repel each other. We can therefore think at first glance that it is impossible to make two nuclei with the same charge meet. It was therefore necessary to find a way to overcome this Coulomb force. This is where the heat factor comes in. Indeed, at a very high temperature the Coulomb “barrier” is overcome and the collision of the nuclei can therefore occur. (On the sun and the stars the temperature is extremely high!)

The reaction chamber of the DIII-D, an experimental tokamak fusion reactor operated by General Atomics in San Diego, which has been used in research since it was completed in the late 1980s. The characteristic torus-shaped chamber is clad with graphite to help withstand the extreme heat. Rswilcox, CC BY-SA 4.0, via Wikimedia Commons

It is necessary to succeed in recreating this temperature range. Another difficulty to solve. The tokamaks (photo above) partially allow this reproduction but the level of temperature produced is not sufficient and the melting becomes very difficult to control.

Reproducing an environment of several hundred million degrees is extremely hard in the laboratory. However, two methods have been found to try to produce the most heat.

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The first is magnetic confinement (case of Tokamak). The fuels, in this case in the form of plasma due to the temperature, are influenced by very powerful magnetic fields which promote fusion.

The second is inertial confinement. Lasers are used to combine nuclei for fusion. These two methods are practical but the heat is not yet sufficient for a truly satisfactory result.

Fusion, currently, is poorly controlled. Its use in electricity production, for example, is not recommended. Moreover, nowadays it takes a lot of energy to produce sufficient heat and we obtain a low efficiency. This is therefore not advantageous, lucrative although for about thirty years progress has been considerable in terms of energy production and efficiency. But this very large-scale production still leaves doubts about its reliability.

The nucleus of an atom is made up of two types of particles called nucleons: positively charged protons and zero charged neutrons. The cohesion of nucleons, and therefore the stability of atoms, is ensured by a short-range force (10^—15 m) called the strong interaction. It opposes the electrostatic force which is, on the contrary, repulsive for charged particles of the same sign (protons). Nuclear physics teaches us that the binding energy, in megaelectronvolts (MeV) per nucleon, is maximum for the iron atom, which is made up of 56 nucleons, which means concretely that the fission of nuclei heavier than iron or the fusion of lighter nuclei releases energy.

The mushroom cloud from the “Mike” shot. Ivy Mike, the first two-stage thermonuclear detonation, 10.4 megatons, November 1, 1952. Photo courtesy of National Nuclear Security Administration / Nevada Site Office, Public domain, via Wikimedia Commons

History

In 1940, the Hungarian-American Edward Teller studied the possibility of using the enormous amount of heat (108 °C, i.e. one hundred million degrees Celsius) produced by the explosion of an atomic fission bomb to start the nuclear fusion process. In 1941, Teller joined the Manhattan Project, which aimed to develop the atomic fusion bomb.

After preliminary work in Chicago with Enrico Fermi, and in Berkeley with Robert Oppenheimer, Teller went to the laboratories of Los Alamos (New Mexico, United States) to work on the atomic bomb under the direction of Oppenheimer. Since the difficulties encountered in making a fission bomb were less, the H-bomb lead was not pursued, much to Teller’s disappointment.

In 1949, when the Soviets detonated their own fission bomb, US intelligence analysis showed that it was a bomb that used plutonium as nuclear fuel. America’s monopoly on the nuclear issue disappears. This news generates a considerable psychological shock, since the United States hoped to be able to retain the monopoly of the military weapon for ten years. Then, they commit to a new epic, the search for a bomb even more powerful than fission: the fusion bomb.

The President of the United States Harry Truman thus asks the Los Alamos laboratory to develop a bomb that works thanks to the fusion of hydrogen nuclei. Oppenheimer is opposed to this decision, as he considers it another instrument of genocide. Teller is in charge of the program. However, his model, despite being reasonable, does not allow him to achieve his goal.

The Polish-American mathematician Stanisław Ulam, in collaboration with C.J. Everett, showed with detailed calculations that Teller’s model was unworkable. Ulam suggests a new method that does succeed. By placing a fission bomb at one end and thermonuclear material at the other end of an enclosure, it is possible to direct the shock waves produced by the fission bomb. These waves compress and ignite the thermonuclear fuel.

At first Teller did not accept the idea, but later understood all its merit and suggested the use of radiation (instead of shock waves) to compress the thermonuclear material. The first H-bomb, Ivy Mike, exploded over Enewetak Atoll (near Bikini, in the Pacific Ocean) on November 1, 1952 to Teller’s satisfaction, with most of the scientific community disagreeing .

Radiation implosion thus became the standard method for creating fusion bombs. Both creators, Ulam and Teller, thus produced their Hydrogen-bomb.

Sources: PinterPandai, AtomicArchive, History, Britannica