Abstract
During the five years I spent at ITER I discovered that people visiting ITER, despite very different origins and backgrounds, have one thing in common: the vast majority of them confuse nuclear fission and nuclear fusion. However, the difference between fusion and fission is indeed fundamental. In modern nuclear fission power plants large atomic nuclei such as uranium or plutonium are split apart releasing large amounts of energy. This energy is stored in the strong bonds that hold the protons and neutrons together in the nucleus; therefore, breaking the nucleus apart releases the energy. In a fusion reactor the opposite process takes place: light atomic nuclei such as hydrogen are heated to several million degrees and will then have enough kinetic energy to overcome their electrostatic repulsion and “fuse” with each other. This releases even larger amounts of energy. Although fusion and fission are fundamentally very different technologies, they are unified under the adjective “nuclear”. To achieve fusion on Earth one must create astronomical temperatures of tens or even hundreds of millions of degrees. For example, the H-bomb (a.k.a. hydrogen bomb or thermonuclear bomb) is actually a double bomb. It contains a primary fission A-bomb (made of uranium or plutonium) that explodes only to compress and heat the gas inside (tritium, deuterium, or lithium deuteride) up to a very high temperature of about 100 million degrees. This triggers hydrogen fusion reactions that constitute the thermonuclear explosion of the bomb. This became clear in the 1950s when scientists realized that fusion holds huge potential for peaceful applications and controlled (nonexplosive) systems. Although the fusion pioneers did not master all the science and technology at that time, it was clear that fusion would be a vastly superior energy source compared with fission. However, these visionary scientists clearly underestimated the many difficulties and technical hurdles they would encounter on the road to fusion that complicated, if not prevented, the road to peaceful application of the technology … This chapter will introduce the principles of nuclear fusion (without, however, let me reassure you right away, turning into a physics handbook) and look into the “tokamak” technology, invented by Russian scientists in the early 1950s, which is currently the most promising to produce fusion energy.
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Notes
- 1.
In the states of matter that we are familiar with (solid, liquid, and gas) nuclei and electrons are bound together to form atoms. In plasma, however, nuclei and electrons are independent of each other. In technical terms atoms have become “ionized”. In plasma positive and negative charges are evenly spaced making plasma electrically neutral even on a very small scale.
- 2.
Most chemical elements exist in several forms called isotopes. Different isotopes of a given element have the same number of protons but a different number of neutrons (hence different masses). In a chemical reaction isotopes behave much the same as each other; in a nuclear reaction they can exhibit very different properties.
- 3.
Clery [1].
- 4.
The acronym comes from the Russian тороидальная камера с магнитными катушками (“toroidal chamber with magnetic coils”).
- 5.
The name derives from the fact that its promoters hoped to achieve temperatures comparable with stellar plasmas with this configuration.
- 6.
The name “poloidal field” comes from comparison with the Earth’s magnetic field, which has a poloidal component (parallel to the North–South axis) and a toroidal component (parallel to the lines of latitude).
- 7.
The electron volt (eV) represents the amount of energy gained by the charge of a single electron moved across an electric potential difference of 1 V. In plasma physics it is common to use the electron volt as a temperature unit. The Boltzmann constant kB is used to make the conversion meaning that 1 eV is equal to 11,605 K. In the ITER tokamak the plasma will reach a temperature of 13 keV, which corresponds to about 150,000,000 K.
- 8.
Cookson [2] .
- 9.
Ball [3].
References
Clery D (2013) A piece of the sun: the quest for fusion energy. Overlook Duckworth, New York
Cookson C (1989, March 23) Nuclear fusion in a test tube. Financial times
Ball P (2019) Lessons from cold fusion, 30 years on. Nature 569:601. https://doi.org/10.1038/d41586-019-01673-x
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Claessens, M. (2020). What Is Nuclear Fusion?. In: ITER: The Giant Fusion Reactor. Copernicus, Cham. https://doi.org/10.1007/978-3-030-27581-5_2
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DOI: https://doi.org/10.1007/978-3-030-27581-5_2
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