Nuclear Fusion
Followers of the good side of world news may be very familiar with research in fusion power. Often advertised as "limitless clean energy", harnessing the power of the stars would be one of the greatest advancements of tech humanity could achieve in history, but it always seems to be 20 years away? No, it isn't. That isn't how innovation works. Plus, the truth is we have already utilized the power of stars. Nuclear fusion is the process of two lighter atomic nuclei fusing to become a single nuclei. Light nuclei (those lighter than Iron) release large amounts of energy that can be harnessed for power. Nuclear fusion reactors contain this reaction while thermonuclear bombs use the fusion process to drive a second fissile stage for a much greater output than conventional nuclear warheads. On top of that, we have achieved controlled fusion of positive gain so commercial fusion should very well be possible.
The civilizations of the Celestial Grove are no strangers to the power of the atom. Almost all of the technologically advanced civilizations, bar the few that have yet to harness their own steam power, have substantial generating capacity for fusion hydrogen and helium isotopes for power. Nuclear fusion bombs have also been used in many war as EMP devices. Large amounts of data on stellar nucleosynthesis (fusion in stars), as well as supernova and neutron merger nucleosynthesis (fusion of heavy elements in supernovas and neutron star collisions). Over the thousands of years of stellar observations, the many sophonts of the Celestial Grove have been witness to many natural events that breed heavier nuclei.
Helium: Hydrogen fusion results in helium products which do accumulate in the cores of stars. Helium-4, the main product, reacts at incredibly high temperatures and may do so explosively in small red giants, or start slowly in higher mass stars as they transition to their giant stages. Helium flashes in the smaller giants are not actually harmful to anything orbiting the star. Although explosive, the energy gets absorbed by the core and is not visible outside of the star. Sensitive electromagnetic equipment on the outside of a ship or probe will likely pick up what little energy does reach the surface, however. Heavier elements: Fusion of heavier elements, such as carbon, oxygen, neon, and silicon can occur naturally in stars. However, such stars have to be incredibly massive. Large portions of these elements come such from large stars. The process of burning through these elements is very similar to that of helium, with flashes that occur incredibly quickly, or pre-degenerate burning in larger stars. However, each stage gets exponentially shorter than the other with higher temperatures and less and less fuel. Stars heavy enough to fuse elements into iron are likely able to go supernova, which fuses endothermic elements heavier than iron.
Instead of superconducting magnets and heaters, inertial confinement fusion instead explosively compresses pellets of frozen fuel until it ignites from the heat. These reactors are less efficient, but burn fuel at very high volumes and thus produce more power on average than magnetic confinement. Such a method of fusion requires large driver lasers, and so is not very common on spacecraft. However, inertial confinement propulsion is popular on super heavy ships that benefit with the higher potential thrust of these engines.
Fusion history is pretty consistent among all species when they discover nuclear science. More often than not, it is nuclear fission research that breeds the eventual progression to nuclear fusion. Often they coincide with weapons research as well. Commercial fission is recognized right away. Splitting an atom is many times easier than fusing the atom. So easy (to the standard of nuclear physics) in fact that it sometimes happens naturally. What is also natural is the question: "If atoms can be split, can we also combine them?" Second generation nuclear bombs could be outfitted with a hydrogen container around the primary and secondary uranium cores that fuses using energy from the primary core in a manner similar to indirect drive inertial confinement fusion. Unfortunately, mimicking the conditions of a nuclear bomb with the "bomb" part is hard. It could take decades, but once a civilization gets started on the nuclear road, it is inevitable that fusion energy will become a thing. The prospect of unlimited clean energy is too good to pass up. Early reactors that gain energy are consistently deuterium-tritium toroidal and inertial confinement because both are viable for those reactions. Reactors become more efficient and the technology scales better before linear reactors become viable and are used on spacecraft for propulsion. As antimatter becomes affordable, antimatter catalyzed fusion will start to be used on interstellar spacecraft. The consistent progression of reactor technology introduces deuterium-helion reactions to the same pattern which commonly replaces DT fusion onboard spacecraft. The road to helium-3 fusion also unlocks the door to deuterium fusion which produces waste that is used in the two most common fusion reactors for power or propulsion. This technology can suddenly make fusion energy a whole lot cheaper which then goes on to benefit spaceflight, making it more accessible and driving a sort of renaissance for interplanetary and interstellar trade. Not to mention cheaper energy for everyone. The progression of this tech eventually does lead to proton-boron and pure helion fusion, but these reactions require more energy for ever diminishing returns. Hydrogenless reactions are only ever done for scientific purposes because of this. Beyond this, any technological capacity to fuse any heavier elements just doesn't exist. Only stars are able to produce necessary conditions.
Cold fusion is a theoretical method of fusing elements at much lower temperatures in artificial environments than typical. High temperatures in reactors are required for the kinetic energy of nuclei to overcome the strong nuclear forces that bind nuclei together, so cold fusion shouldn't otherwise be possible using any conventional method. However, possibilities of string field manipulation could prompt the ability to fuse elements at any temperature. The potential energy requirements of such a system would be tremendous, which negates any gains of commercial power generation. Cold fusion could, however, be used to produce heavy elements in very high quantities that otherwise wouldn't be found naturally
Nuclear fusion - britannica.com
Small-scale fusion tackles energy, space applications - pnas.org
Stellar nucleosynthesis - wikipedia.org
Using Lunar Helium-3 to Generate Nuclear Power Without the Production of Nuclear Waste - wisc.edu (PDF)
Natural Fusion
Stellar Nucleosynthesis
Hydrogen: There are multiple processes involved in the natural fusion of stars that occur differently depending on the mass, temperature, and material in regions where fusion can occur. In low mass main sequence stars, hydrogen protons react with each other to produce deuterium, which reacts with another proton to produce helium-3. The helium-3 then reacts with another same nuclei to produce helium-4 and two hydrogen nuclei. Higher mass stars will gain more energy from the Carbon-Nitrogen-Oxygen (CNO) catalytic cycle which react hydrogen nuclei with C, N, and O nuclei until Nitrogen-15 reacts with hydrogen to produce helium-4 and Carbon-12 that restarts the cycle.Helium: Hydrogen fusion results in helium products which do accumulate in the cores of stars. Helium-4, the main product, reacts at incredibly high temperatures and may do so explosively in small red giants, or start slowly in higher mass stars as they transition to their giant stages. Helium flashes in the smaller giants are not actually harmful to anything orbiting the star. Although explosive, the energy gets absorbed by the core and is not visible outside of the star. Sensitive electromagnetic equipment on the outside of a ship or probe will likely pick up what little energy does reach the surface, however. Heavier elements: Fusion of heavier elements, such as carbon, oxygen, neon, and silicon can occur naturally in stars. However, such stars have to be incredibly massive. Large portions of these elements come such from large stars. The process of burning through these elements is very similar to that of helium, with flashes that occur incredibly quickly, or pre-degenerate burning in larger stars. However, each stage gets exponentially shorter than the other with higher temperatures and less and less fuel. Stars heavy enough to fuse elements into iron are likely able to go supernova, which fuses endothermic elements heavier than iron.
Supernova Nucleosynthesis
The violent deaths of stars are incredibly energetic and briefly produce temperatures and pressures that far surpass any other environment in the universe. Under such conditions, practically all elements can fuse together, including heavy elements that require energy input. Many heavy elements are created under these conditions. Products like copper, tungsten, and lead are examples of such.Neutron Star Merger Nucleosynthesis
The heaviest elements, except those with no stable isotopes, are produced in larger quantities in the merging of neutron stars. The dead remains of high mass stars that escaped becoming black holes have some incredibly unique conditions that make these celestial bodies perhaps one of the worst places to be in the universe. Dead remains of stars full of degenerate matter at pressures and densities so great that protons and electrons are forced together to create neutrons. Mergers of neutron stars release so much energy that incredibly heavy elements can created. Elements such as gold, iridium, and uranium are fused in neutron star mergers.Artificial Fusion
Deuterium-Deuterium Fusion
Deuterium fusion (DD) is a low energy, high temperature fusion reaction. It has little commercial power value, but instead serves as a production mode for tritium and helium-3. In a deuterium reaction, the isotope reacts with itself to produce either a low-energy neutron and 3He nuclei, or a proton and tritium. Such reactors are quick cycle reactors, meaning they undergo fusion in rapid pulses. This is done to minimize secondary reactions that waste products. The products are filtered out of the plasma with remaining deuterium being returned to the system. The tritium and helium-3 are deionized and cooled to cryogenic temperatures to be shipped to customers.Deuterium-Tritium Fusion
Deuterium and Tritium are two heavy isotopes of hydrogen and are among the most efficient at fusing. Deuterium is one of the most common isotopes of hydrogen, but tritium is unstable and occurs only in trace amounts naturally. The nuclei fuse at the lowest reactor temperatures of any reaction and produce large amounts of energy, but almost all of the energy is in a stray neutron that requires large amounts of shielding that will degrade and become radioactive under prolonged neutron exposure. These reactions are more common in power stations because they can afford the high shielding and regular replacement.Deuterium-Helion Reaction
Deuterium and hydrogen-3, also known as helion, produce an aneutronic reaction and more marginally more energy than a DT reaction. Although slightly more energetic than DT fusion, the heat required to instigated D3He fusion is substantially higher than its contemporary. Consequently, there is less excess energy. However, D3He fusion only produces a proton which can conveniently be guided by the magnetic field that is already required to sustain the reaction. So, helion reactors do not require impressively heavy amounts of shielding. In fact, you could probably get away with having the reaction chamber fully exposed to the vacuum of space which is incredibly beneficial to spacecraft. Another added benefit to deuterium-helion reactors is that the temperatures required for the helium to fuse is also high enough for the deuterium to fuse with itself. This reaction produces tritium, and a low energy neutron. The tritium can be recovered and recycled for use in deuterium-tritium reactors or left to decay into helium-3. Although, DD fusion is very inefficient so some might say that it is a downside.Artificial Fusion Methods
Magnetic Confinement
Magnetic confinement fusion is the most common way to contain fusion reactants and products. It is relatively simple and uses commonly available superconductors. Magnetic confinements comes in multiple flavors such as: toroidal, spherical, and linear. Toroidal and spherical reactors are more often recognized as tokamaks and spheromaks in our reality. The former two reactors are similar in that they confine plasma in a circular formation, but spherical reactors lack a central solenoid and use the nature of plasma to confine itself. Spherical reactors don't exist in commercial markets. Lack of a central solenoid leads to instabilities in the plasma, causing the containment field to disintegrate. Linear confinement, which is what fusion jet propulsion use, surrounds the plasma stream like a pipe.Inertial Confinement
Main article: Inertial Confinement ReactorInstead of superconducting magnets and heaters, inertial confinement fusion instead explosively compresses pellets of frozen fuel until it ignites from the heat. These reactors are less efficient, but burn fuel at very high volumes and thus produce more power on average than magnetic confinement. Such a method of fusion requires large driver lasers, and so is not very common on spacecraft. However, inertial confinement propulsion is popular on super heavy ships that benefit with the higher potential thrust of these engines.
History
Fusion history is pretty consistent among all species when they discover nuclear science. More often than not, it is nuclear fission research that breeds the eventual progression to nuclear fusion. Often they coincide with weapons research as well. Commercial fission is recognized right away. Splitting an atom is many times easier than fusing the atom. So easy (to the standard of nuclear physics) in fact that it sometimes happens naturally. What is also natural is the question: "If atoms can be split, can we also combine them?" Second generation nuclear bombs could be outfitted with a hydrogen container around the primary and secondary uranium cores that fuses using energy from the primary core in a manner similar to indirect drive inertial confinement fusion. Unfortunately, mimicking the conditions of a nuclear bomb with the "bomb" part is hard. It could take decades, but once a civilization gets started on the nuclear road, it is inevitable that fusion energy will become a thing. The prospect of unlimited clean energy is too good to pass up. Early reactors that gain energy are consistently deuterium-tritium toroidal and inertial confinement because both are viable for those reactions. Reactors become more efficient and the technology scales better before linear reactors become viable and are used on spacecraft for propulsion. As antimatter becomes affordable, antimatter catalyzed fusion will start to be used on interstellar spacecraft. The consistent progression of reactor technology introduces deuterium-helion reactions to the same pattern which commonly replaces DT fusion onboard spacecraft. The road to helium-3 fusion also unlocks the door to deuterium fusion which produces waste that is used in the two most common fusion reactors for power or propulsion. This technology can suddenly make fusion energy a whole lot cheaper which then goes on to benefit spaceflight, making it more accessible and driving a sort of renaissance for interplanetary and interstellar trade. Not to mention cheaper energy for everyone. The progression of this tech eventually does lead to proton-boron and pure helion fusion, but these reactions require more energy for ever diminishing returns. Hydrogenless reactions are only ever done for scientific purposes because of this. Beyond this, any technological capacity to fuse any heavier elements just doesn't exist. Only stars are able to produce necessary conditions.
Cold Fusion
Cold fusion is a theoretical method of fusing elements at much lower temperatures in artificial environments than typical. High temperatures in reactors are required for the kinetic energy of nuclei to overcome the strong nuclear forces that bind nuclei together, so cold fusion shouldn't otherwise be possible using any conventional method. However, possibilities of string field manipulation could prompt the ability to fuse elements at any temperature. The potential energy requirements of such a system would be tremendous, which negates any gains of commercial power generation. Cold fusion could, however, be used to produce heavy elements in very high quantities that otherwise wouldn't be found naturally
References
Nuclear fusion - britannica.com
Small-scale fusion tackles energy, space applications - pnas.org
Stellar nucleosynthesis - wikipedia.org
Using Lunar Helium-3 to Generate Nuclear Power Without the Production of Nuclear Waste - wisc.edu (PDF)
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