EFDA (1999 — 2013) has been followed by EUROfusion , which is a consortium of national fusion research institutes located in the European Union and Switzerland.
90-638: The European Union has a strongly coordinated nuclear fusion research programme. At the European level, the so-called EURATOM Treaty is the international legal framework under which member states cooperate in the fields of nuclear fusion research. The European Fusion Development Agreement ( EFDA ) is an agreement between European fusion research institutions and the European Commission (which represents Euratom ) to strengthen their coordination and collaboration, and to participate in collective activities in
180-515: A 90 million degree plasma for a record time of six minutes. This is a tokamak style reactor which is the same style as the upcoming ITER reactor. The release of energy with the fusion of light elements is due to the interplay of two opposing forces: the nuclear force , a manifestation of the strong interaction , which holds protons and neutrons tightly together in the atomic nucleus ; and the Coulomb force , which causes positively charged protons in
270-451: A flux of neutrons. Hundreds of neutron generators are produced annually for use in the petroleum industry where they are used in measurement equipment for locating and mapping oil reserves. A number of attempts to recirculate the ions that "miss" collisions have been made over the years. One of the better-known attempts in the 1970s was Migma , which used a unique particle storage ring to capture ions into circular orbits and return them to
360-409: A fully artificial nuclear reaction and nuclear transmutation was achieved by Rutherford's colleagues John Cockcroft and Ernest Walton , who used artificially accelerated protons against lithium-7, to split the nucleus into two alpha particles. The feat was popularly known as "splitting the atom ", although it was not the modern nuclear fission reaction later (in 1938) discovered in heavy elements by
450-500: A heavy and light nucleus; while reactions between two light nuclei are the most common ones. Neutrons , on the other hand, have no electric charge to cause repulsion, and are able to initiate a nuclear reaction at very low energies. In fact, at extremely low particle energies (corresponding, say, to thermal equilibrium at room temperature ), the neutron's de Broglie wavelength is greatly increased, possibly greatly increasing its capture cross-section, at energies close to resonances of
540-494: A lab for nuclear fusion power production is completely impractical. Because nuclear reaction rates depend on density as well as temperature and most fusion schemes operate at relatively low densities, those methods are strongly dependent on higher temperatures. The fusion rate as a function of temperature (exp(− E / kT )), leads to the need to achieve temperatures in terrestrial reactors 10–100 times higher than in stellar interiors: T ≈ (0.1–1.0) × 10 K . In artificial fusion,
630-416: A miniature Voitenko compressor , where a plane diaphragm was driven by the implosion wave into a secondary small spherical cavity that contained pure deuterium gas at one atmosphere. There are also electrostatic confinement fusion devices. These devices confine ions using electrostatic fields. The best known is the fusor . This device has a cathode inside an anode wire cage. Positive ions fly towards
720-427: A more massive star undergoes a violent supernova at the end of its life, a process known as supernova nucleosynthesis . A substantial energy barrier of electrostatic forces must be overcome before fusion can occur. At large distances, two naked nuclei repel one another because of the repulsive electrostatic force between their positively charged protons. If two nuclei can be brought close enough together, however,
810-416: A nucleus are identical to each other, the goal of distinguishing one from the other, such as which one is in the interior and which is on the surface, is in fact meaningless, and the inclusion of quantum mechanics is therefore necessary for proper calculations. The electrostatic force, on the other hand, is an inverse-square force , so a proton added to a nucleus will feel an electrostatic repulsion from all
900-454: A nucleus have more neighboring nucleons than those on the surface. Since smaller nuclei have a larger surface-area-to-volume ratio, the binding energy per nucleon due to the nuclear force generally increases with the size of the nucleus but approaches a limiting value corresponding to that of a nucleus with a diameter of about four nucleons. It is important to keep in mind that nucleons are quantum objects . So, for example, since two neutrons in
990-438: A nucleus interacts with another nucleus or particle, they then separate without changing the nature of any nuclide, the process is simply referred to as a type of nuclear scattering , rather than a nuclear reaction. In principle, a reaction can involve more than two particles colliding , but because the probability of three or more nuclei to meet at the same time at the same place is much less than for two nuclei, such an event
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#17330860239441080-471: A relatively small mass and a relatively large binding energy per nucleon . Fusion of nuclei lighter than these releases energy (an exothermic process), while the fusion of heavier nuclei results in energy retained by the product nucleons, and the resulting reaction is endothermic . The opposite is true for the reverse process, called nuclear fission . Nuclear fusion uses lighter elements, such as hydrogen and helium , which are in general more fusible; while
1170-422: A significant fraction of the fuel before it has dissipated. To achieve these extreme conditions, the initially cold fuel must be explosively compressed. Inertial confinement is used in the hydrogen bomb , where the driver is x-rays created by a fission bomb. Inertial confinement is also attempted in "controlled" nuclear fusion, where the driver is a laser , ion , or electron beam, or a Z-pinch . Another method
1260-525: A small amount of deuterium–tritium gas to enhance the fission yield. The first thermonuclear weapon detonation, where the vast majority of the yield comes from fusion, was the 1952 Ivy Mike test of a liquid deuterium-fusing device. While fusion bomb detonations were loosely considered for energy production , the possibility of controlled and sustained reactions remained the scientific focus for peaceful fusion power. Research into developing controlled fusion inside fusion reactors has been ongoing since
1350-527: A solar-core temperature of 14 million kelvin. The net result is the fusion of four protons into one alpha particle , with the release of two positrons and two neutrinos (which changes two of the protons into neutrons), and energy. In heavier stars, the CNO cycle and other processes are more important. As a star uses up a substantial fraction of its hydrogen, it begins to synthesize heavier elements. The heaviest elements are synthesized by fusion that occurs when
1440-424: A static fuel-infused target, known as beam–target fusion, or by accelerating two streams of ions towards each other, beam–beam fusion. The key problem with accelerator-based fusion (and with cold targets in general) is that fusion cross sections are many orders of magnitude lower than Coulomb interaction cross-sections. Therefore, the vast majority of ions expend their energy emitting bremsstrahlung radiation and
1530-448: A toroidal reactor that theoretically will deliver ten times more fusion energy than the amount needed to heat plasma to the required temperatures are in development (see ITER ). The ITER facility is expected to finish its construction phase in 2025. It will start commissioning the reactor that same year and initiate plasma experiments in 2025, but is not expected to begin full deuterium–tritium fusion until 2035. Private companies pursuing
1620-402: A useful energy source, a fusion reaction must satisfy several criteria. It must: Nuclear reaction In nuclear physics and nuclear chemistry , a nuclear reaction is a process in which two nuclei , or a nucleus and an external subatomic particle , collide to produce one or more new nuclides . Thus, a nuclear reaction must cause a transformation of at least one nuclide to another. If
1710-406: A way that a helium nucleus, with its extremely tight binding, is one of the products. Using deuterium–tritium fuel, the resulting energy barrier is about 0.1 MeV. In comparison, the energy needed to remove an electron from hydrogen is 13.6 eV. The (intermediate) result of the fusion is an unstable He nucleus, which immediately ejects a neutron with 14.1 MeV. The recoil energy of
1800-423: Is a technique using particle accelerators to achieve particle kinetic energies sufficient to induce light-ion fusion reactions. Accelerating light ions is relatively easy, and can be done in an efficient manner—requiring only a vacuum tube, a pair of electrodes, and a high-voltage transformer; fusion can be observed with as little as 10 kV between the electrodes. The system can be arranged to accelerate ions into
1890-631: Is exceptionally rare (see triple alpha process for an example very close to a three-body nuclear reaction). The term "nuclear reaction" may refer either to a change in a nuclide induced by collision with another particle or to a spontaneous change of a nuclide without collision. Natural nuclear reactions occur in the interaction between cosmic rays and matter, and nuclear reactions can be employed artificially to obtain nuclear energy, at an adjustable rate, on-demand. Nuclear chain reactions in fissionable materials produce induced nuclear fission . Various nuclear fusion reactions of light elements power
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#17330860239441980-729: Is hosted by the CCFE Archived 2020-10-28 at the Wayback Machine laboratory in Culham (UK), home of the Joint European Torus facilities. A large number of scientists and engineers from the associated laboratories work together on different projects of EFDA. The main task of the Close Support Units is to ensure that these diverse activities are integrated in a coordinated European Fusion Programme. The EFDA management consists of
2070-433: Is how to confine the hot plasma. Due to the high temperature, the plasma cannot be in direct contact with any solid material, so it has to be located in a vacuum . Also, high temperatures imply high pressures. The plasma tends to expand immediately and some force is necessary to act against it. This force can take one of three forms: gravitation in stars, magnetic forces in magnetic confinement fusion reactors, or inertial as
2160-436: Is more stable, the iron isotope Fe is an order of magnitude more common. This is due to the fact that there is no easy way for stars to create Ni through the alpha process . An exception to this general trend is the helium-4 nucleus, whose binding energy is higher than that of lithium , the next heavier element. This is because protons and neutrons are fermions , which according to
2250-493: Is much larger than in chemical reactions , because the binding energy that holds a nucleus together is greater than the energy that holds electrons to a nucleus. For example, the ionization energy gained by adding an electron to a hydrogen nucleus is 13.6 eV —less than one-millionth of the 17.6 MeV released in the deuterium – tritium (D–T) reaction shown in the adjacent diagram. Fusion reactions have an energy density many times greater than nuclear fission ;
2340-457: Is the stellar nucleosynthesis that powers stars , including the Sun. In the 20th century, it was recognized that the energy released from nuclear fusion reactions accounts for the longevity of stellar heat and light. The fusion of nuclei in a star, starting from its initial hydrogen and helium abundance, provides that energy and synthesizes new nuclei. Different reaction chains are involved, depending on
2430-408: Is to merge two FRC's rotating in opposite directions, which is being actively studied by Helion Energy . Because these approaches all have ion energies well beyond the Coulomb barrier , they often suggest the use of alternative fuel cycles like p- B that are too difficult to attempt using conventional approaches. Muon-catalyzed fusion is a fusion process that occurs at ordinary temperatures. It
2520-407: Is to use conventional high explosive material to compress a fuel to fusion conditions. The UTIAS explosive-driven-implosion facility was used to produce stable, centred and focused hemispherical implosions to generate neutrons from D-D reactions. The simplest and most direct method proved to be in a predetonated stoichiometric mixture of deuterium - oxygen . The other successful method was using
2610-949: Is useful to perform an average over the distributions of the product of cross-section and velocity. This average is called the 'reactivity', denoted ⟨ σv ⟩ . The reaction rate (fusions per volume per time) is ⟨ σv ⟩ times the product of the reactant number densities: If a species of nuclei is reacting with a nucleus like itself, such as the DD reaction, then the product n 1 n 2 {\displaystyle n_{1}n_{2}} must be replaced by n 2 / 2 {\displaystyle n^{2}/2} . ⟨ σ v ⟩ {\displaystyle \langle \sigma v\rangle } increases from virtually zero at room temperatures up to meaningful magnitudes at temperatures of 10 – 100 keV. At these temperatures, well above typical ionization energies (13.6 eV in
2700-538: The Lawson criterion , the energy of accidental collisions within the plasma is high enough to overcome the Coulomb barrier and the particles may fuse together. In a deuterium–tritium fusion reaction , for example, the energy necessary to overcome the Coulomb barrier is 0.1 MeV . Converting between energy and temperature shows that the 0.1 MeV barrier would be overcome at a temperature in excess of 1.2 billion kelvin . There are two effects that are needed to lower
2790-531: The Pauli exclusion principle cannot exist in the same nucleus in exactly the same state. Each proton or neutron's energy state in a nucleus can accommodate both a spin up particle and a spin down particle. Helium-4 has an anomalously large binding energy because its nucleus consists of two protons and two neutrons (it is a doubly magic nucleus), so all four of its nucleons can be in the ground state. Any additional nucleons would have to go into higher energy states. Indeed,
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2880-474: The Polywell , MIX POPS and Marble concepts. At the temperatures and densities in stellar cores, the rates of fusion reactions are notoriously slow. For example, at solar core temperature ( T ≈ 15 MK) and density (160 g/cm ), the energy release rate is only 276 μW/cm —about a quarter of the volumetric rate at which a resting human body generates heat. Thus, reproduction of stellar core conditions in
2970-597: The United States Department of Energy announced that on 5 December 2022, they had successfully accomplished break-even fusion, "delivering 2.05 megajoules (MJ) of energy to the target, resulting in 3.15 MJ of fusion energy output." Prior to this breakthrough, controlled fusion reactions had been unable to produce break-even (self-sustaining) controlled fusion. The two most advanced approaches for it are magnetic confinement (toroid designs) and inertial confinement (laser designs). Workable designs for
3060-410: The binding energy becomes negative and very heavy nuclei (all with more than 208 nucleons, corresponding to a diameter of about 6 nucleons) are not stable. The four most tightly bound nuclei, in decreasing order of binding energy per nucleon, are Ni , Fe , Fe , and Ni . Even though the nickel isotope , Ni ,
3150-519: The 1930s, with Los Alamos National Laboratory 's Scylla I device producing the first laboratory thermonuclear fusion in 1958, but the technology is still in its developmental phase. The US National Ignition Facility , which uses laser-driven inertial confinement fusion , was designed with a goal of break-even fusion; the first large-scale laser target experiments were performed in June 2009 and ignition experiments began in early 2011. On 13 December 2022,
3240-515: The Coulomb barrier completely. If they have nearly enough energy, they can tunnel through the remaining barrier. For these reasons fuel at lower temperatures will still undergo fusion events, at a lower rate. Thermonuclear fusion is one of the methods being researched in the attempts to produce fusion power . If thermonuclear fusion becomes favorable to use, it would significantly reduce the world's carbon footprint . Accelerator-based light-ion fusion
3330-745: The EFDA Leader (Dr. Francesco Romanelli) and the EFDA-Associate Leader for JET (Dr. Francesco Romanelli). In order to achieve its objectives EFDA conducts the following group of activities: EFDA coordinates a range of activities to be carried out by the Associations in 7 key physics and technology areas. The implementation of these activities benefits from structures so called Task Forces and Topical Groups. The European Task Forces on Plasma Wall Interaction (PWI) and on Integrated Tokamak Modelling (ITM) set up respectively in 2002 and 2003. To strengthen
3420-524: The European Domestic Agency called " Fusion for Energy ", also called F4E, in March 2007. With the appearance of F4E EFDA´s role has changed and it has been reorganised. A revised European Fusion Development Agreement entered into force on 1 January 2008 focuses on research coordination with two main objectives: to prepare for the operation and exploitation of ITER and to further develop and consolidate
3510-603: The European contribution to large scale international collaborations, such as the ITER -project. 2008 has brought a significant change to the structure of the European Fusion Programme. The change was triggered by the signature of the ITER agreement at the end of 2006. The ITER parties had agreed to provide contributions to ITER through legal entities referred to as "Domestic Agencies". Europe has fulfilled its obligation by launching
3600-479: The German scientists Otto Hahn , Lise Meitner , and Fritz Strassmann . Nuclear reactions may be shown in a form similar to chemical equations, for which invariant mass must balance for each side of the equation, and in which transformations of particles must follow certain conservation laws, such as conservation of charge and baryon number (total atomic mass number ). An example of this notation follows: To balance
3690-499: The Sun fuses 620 million metric tons of hydrogen and makes 616 million metric tons of helium each second. The fusion of lighter elements in stars releases energy and the mass that always accompanies it. For example, in the fusion of two hydrogen nuclei to form helium, 0.645% of the mass is carried away in the form of kinetic energy of an alpha particle or other forms of energy, such as electromagnetic radiation. It takes considerable energy to force nuclei to fuse, even those of
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3780-456: The actual temperature. One is the fact that temperature is the average kinetic energy, implying that some nuclei at this temperature would actually have much higher energy than 0.1 MeV, while others would be much lower. It is the nuclei in the high-energy tail of the velocity distribution that account for most of the fusion reactions. The other effect is quantum tunnelling . The nuclei do not actually have to have enough energy to overcome
3870-454: The best-known neutron reactions are neutron scattering , neutron capture , and nuclear fission , for some light nuclei (especially odd-odd nuclei ) the most probable reaction with a thermal neutron is a transfer reaction: Some reactions are only possible with fast neutrons : Either a low-energy projectile is absorbed or a higher energy particle transfers energy to the nucleus, leaving it with too much energy to be fully bound together. On
3960-462: The cage, by generating the field using a non-neutral cloud. These include a plasma oscillating device, a Penning trap and the polywell . The technology is relatively immature, however, and many scientific and engineering questions remain. The most well known Inertial electrostatic confinement approach is the fusor . Starting in 1999, a number of amateurs have been able to do amateur fusion using these homemade devices. Other IEC devices include:
4050-503: The co-ordination in other key areas five Topical Groups have been set up in 2008: on Fusion Materials Development , Diagnostics , Heating and Current Drive , Transport and Plasma Stability and Control . Nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei , usually deuterium and tritium (hydrogen isotopes ), combine to form one or more different atomic nuclei and subatomic particles ( neutrons or protons ). The difference in mass between
4140-468: The commercialization of nuclear fusion received $ 2.6 billion in private funding in 2021 alone, going to many notable startups including but not limited to Commonwealth Fusion Systems , Helion Energy Inc ., General Fusion , TAE Technologies Inc. and Zap Energy Inc. One of the most recent breakthroughs to date in maintaining a sustained fusion reaction occurred in France's WEST fusion reactor. It maintained
4230-424: The course of a reaction ( exothermic reaction ) or kinetic energy may have to be supplied for the reaction to take place ( endothermic reaction ). This can be calculated by reference to a table of very accurate particle rest masses, as follows: according to the reference tables, the 3 Li nucleus has a standard atomic weight of 6.015 atomic mass units (abbreviated u ), the deuterium has 2.014 u, and
4320-449: The current advanced technical state. Thermonuclear fusion is the process of atomic nuclei combining or "fusing" using high temperatures to drive them close enough together for this to become possible. Such temperatures cause the matter to become a plasma and, if confined, fusion reactions may occur due to collisions with extreme thermal kinetic energies of the particles. There are two forms of thermonuclear fusion: uncontrolled , in which
4410-404: The electrostatic repulsion can be overcome by the quantum effect in which nuclei can tunnel through coulomb forces. When a nucleon such as a proton or neutron is added to a nucleus, the nuclear force attracts it to all the other nucleons of the nucleus (if the atom is small enough), but primarily to its immediate neighbors due to the short range of the force. The nucleons in the interior of
4500-620: The energy and the flux of the incident particles, and the reaction cross section . An example of a large repository of reaction rates is the REACLIB database, as maintained by the Joint Institute for Nuclear Astrophysics . In the initial collision which begins the reaction, the particles must approach closely enough so that the short-range strong force can affect them. As most common nuclear particles are positively charged, this means they must overcome considerable electrostatic repulsion before
4590-542: The energy production of the Sun and stars. In 1919, Ernest Rutherford was able to accomplish transmutation of nitrogen into oxygen at the University of Manchester, using alpha particles directed at nitrogen N + α → O + p. This was the first observation of an induced nuclear reaction, that is, a reaction in which particles from one decay are used to transform another atomic nucleus. Eventually, in 1932 at Cambridge University,
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#17330860239444680-482: The energy released is 0.0238 × 931 MeV = 22.2 MeV . Expressed differently: the mass is reduced by 0.3%, corresponding to 0.3% of 90 PJ/kg is 270 TJ/kg. This is a large amount of energy for a nuclear reaction; the amount is so high because the binding energy per nucleon of the helium-4 nucleus is unusually high because the He-4 nucleus is " doubly magic ". (The He-4 nucleus is unusually stable and tightly bound for
4770-750: The equation above for mass, charge and mass number, the second nucleus to the right must have atomic number 2 and mass number 4; it is therefore also helium-4. The complete equation therefore reads: or more simply: Instead of using the full equations in the style above, in many situations a compact notation is used to describe nuclear reactions. This style of the form A(b,c)D is equivalent to A + b producing c + D. Common light particles are often abbreviated in this shorthand, typically p for proton, n for neutron, d for deuteron , α representing an alpha particle or helium-4 , β for beta particle or electron, γ for gamma photon , etc. The reaction above would be written as Li(d,α)α. Kinetic energy may be released during
4860-415: The extra energy from the net attraction of particles. For larger nuclei , however, no energy is released, because the nuclear force is short-range and cannot act across larger nuclei. Fusion powers stars and produces virtually all elements in a process called nucleosynthesis . The Sun is a main-sequence star, and, as such, generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core,
4950-502: The field of nuclear fusion research. In Europe, fusion research takes place in a great number of research institutes and universities. In each member state of the European Fusion Programme at least one research organisation has a "Contract of Association" with the European Commission. All the fusion research organisations and institutions of a country are connected to the program through this (these) contracted organisation(s). After
5040-516: The fusion reaction may occur before the plasma starts to expand, so the plasma's inertia is keeping the material together. One force capable of confining the fuel well enough to satisfy the Lawson criterion is gravity . The mass needed, however, is so great that gravitational confinement is only found in stars —the least massive stars capable of sustained fusion are red dwarfs , while brown dwarfs are able to fuse deuterium and lithium if they are of sufficient mass. In stars heavy enough , after
5130-402: The heavier elements, such as uranium , thorium and plutonium , are more fissionable. The extreme astrophysical event of a supernova can produce enough energy to fuse nuclei into elements heavier than iron. American chemist William Draper Harkins was the first to propose the concept of nuclear fusion in 1915. Then in 1921, Arthur Eddington suggested hydrogen–helium fusion could be
5220-444: The helium-4 nucleus has 4.0026 u. Thus: In a nuclear reaction, the total (relativistic) energy is conserved . The "missing" rest mass must therefore reappear as kinetic energy released in the reaction; its source is the nuclear binding energy . Using Einstein's mass-energy equivalence formula E = mc , the amount of energy released can be determined. We first need the energy equivalent of one atomic mass unit : Hence,
5310-453: The helium-4 nucleus is so tightly bound that it is commonly treated as a single quantum mechanical particle in nuclear physics, namely, the alpha particle . The situation is similar if two nuclei are brought together. As they approach each other, all the protons in one nucleus repel all the protons in the other. Not until the two nuclei actually come close enough for long enough so the strong attractive nuclear force can take over and overcome
5400-458: The hydrogen case), the fusion reactants exist in a plasma state. The significance of ⟨ σ v ⟩ {\displaystyle \langle \sigma v\rangle } as a function of temperature in a device with a particular energy confinement time is found by considering the Lawson criterion . This is an extremely challenging barrier to overcome on Earth, which explains why fusion research has taken many years to reach
5490-403: The ionization of atoms of the target. Devices referred to as sealed-tube neutron generators are particularly relevant to this discussion. These small devices are miniature particle accelerators filled with deuterium and tritium gas in an arrangement that allows ions of those nuclei to be accelerated against hydride targets, also containing deuterium and tritium, where fusion takes place, releasing
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#17330860239445580-570: The knowledge base needed for overall fusion development and in particular for DEMO, the first electricity producing experimental fusion power plant being built after ITER. EFDA has two locations, which each house a so-called Close Support Unit (CSU), responsible for part of EFDA's activities. The EFDA-CSU Garching is located in Garching, near Munich (Germany), and is hosted by the German Max-Planck Institut für Plasmaphysik . EFDA-CSU Culham
5670-471: The lightest element, hydrogen . When accelerated to high enough speeds, nuclei can overcome this electrostatic repulsion and be brought close enough such that the attractive nuclear force is greater than the repulsive Coulomb force. The strong force grows rapidly once the nuclei are close enough, and the fusing nucleons can essentially "fall" into each other and the result is fusion; this is an exothermic process . Energy released in most nuclear reactions
5760-516: The mass of the star (and therefore the pressure and temperature in its core). Around 1920, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars . At that time, the source of stellar energy was unknown; Eddington correctly speculated that the source was fusion of hydrogen into helium, liberating enormous energy according to Einstein's equation E = mc . This
5850-496: The name of the contract, the groups of fusion research organisations of the member states are called "Associations". The European Fusion Development Agreement (EFDA) was created in 1999. Until 2008 EFDA was responsible for the exploitation of the Joint European Torus, the coordination and support of fusion-related research & development activities carried out by the Associations and by European Industry and coordination of
5940-417: The negative inner cage, and are heated by the electric field in the process. If they miss the inner cage they can collide and fuse. Ions typically hit the cathode, however, creating prohibitory high conduction losses. Also, fusion rates in fusors are very low due to competing physical effects, such as energy loss in the form of light radiation. Designs have been proposed to avoid the problems associated with
6030-510: The nuclei involved. Thus low-energy neutrons may be even more reactive than high-energy neutrons. While the number of possible nuclear reactions is immense, there are several types that are more common, or otherwise notable. Some examples include: An intermediate energy projectile transfers energy or picks up or loses nucleons to the nucleus in a single quick (10 second) event. Energy and momentum transfer are relatively small. These are particularly useful in experimental nuclear physics, because
6120-419: The nucleus to repel each other. Lighter nuclei (nuclei smaller than iron and nickel) are sufficiently small and proton-poor to allow the nuclear force to overcome the Coulomb force. This is because the nucleus is sufficiently small that all nucleons feel the short-range attractive force at least as strongly as they feel the infinite-range Coulomb repulsion. Building up nuclei from lighter nuclei by fusion releases
6210-478: The one hand, it is the difference between the sums of kinetic energies on the final side and on the initial side. But on the other hand, it is also the difference between the nuclear rest masses on the initial side and on the final side (in this way, we have calculated the Q-value above). If the reaction equation is balanced, that does not mean that the reaction really occurs. The rate at which reactions occur depends on
6300-406: The other protons in the nucleus. The electrostatic energy per nucleon due to the electrostatic force thus increases without limit as nuclei atomic number grows. The net result of the opposing electrostatic and strong nuclear forces is that the binding energy per nucleon generally increases with increasing size, up to the elements iron and nickel , and then decreases for heavier nuclei. Eventually,
6390-410: The outer parts of the stars over long periods of time, by absorbing energy from fusion in the inside of the star, by absorbing neutrons that are emitted from the fusion process. All of the elements heavier than iron have some potential energy to release, in theory. At the extremely heavy end of element production, these heavier elements can produce energy in the process of being split again back toward
6480-424: The primary fuel is not constrained to be protons and higher temperatures can be used, so reactions with larger cross-sections are chosen. Another concern is the production of neutrons, which activate the reactor structure radiologically, but also have the advantages of allowing volumetric extraction of the fusion energy and tritium breeding. Reactions that release no neutrons are referred to as aneutronic . To be
6570-435: The primary source of stellar energy. Quantum tunneling was discovered by Friedrich Hund in 1927, and shortly afterwards Robert Atkinson and Fritz Houtermans used the measured masses of light elements to demonstrate that large amounts of energy could be released by fusing small nuclei. Building on the early experiments in artificial nuclear transmutation by Patrick Blackett , laboratory fusion of hydrogen isotopes
6660-543: The product nucleus is metastable, this is indicated by placing an asterisk ("*") next to its atomic number. This energy is eventually released through nuclear decay . A small amount of energy may also emerge in the form of X-rays . Generally, the product nucleus has a different atomic number, and thus the configuration of its electron shells is wrong. As the electrons rearrange themselves and drop to lower energy levels, internal transition X-rays (X-rays with precisely defined emission lines ) may be emitted. In writing down
6750-527: The reactants and products is manifested as either the release or absorption of energy . This difference in mass arises due to the difference in nuclear binding energy between the atomic nuclei before and after the reaction. Nuclear fusion is the process that powers active or main-sequence stars and other high-magnitude stars, where large amounts of energy are released . A nuclear fusion process that produces atomic nuclei lighter than iron-56 or nickel-62 will generally release energy. These elements have
6840-431: The reaction area. Theoretical calculations made during funding reviews pointed out that the system would have significant difficulty scaling up to contain enough fusion fuel to be relevant as a power source. In the 1990s, a new arrangement using a field-reversed configuration (FRC) as the storage system was proposed by Norman Rostoker and continues to be studied by TAE Technologies as of 2021 . A closely related approach
6930-475: The reaction can begin. Even if the target nucleus is part of a neutral atom , the other particle must penetrate well beyond the electron cloud and closely approach the nucleus, which is positively charged. Thus, such particles must be first accelerated to high energy, for example by: Also, since the force of repulsion is proportional to the product of the two charges, reactions between heavy nuclei are rarer, and require higher initiating energy, than those between
7020-426: The reaction equation, in a way analogous to a chemical equation , one may, in addition, give the reaction energy on the right side: For the particular case discussed above, the reaction energy has already been calculated as Q = 22.2 MeV. Hence: The reaction energy (the "Q-value") is positive for exothermal reactions and negative for endothermal reactions, opposite to the similar expression in chemistry . On
7110-594: The reaction mechanisms are often simple enough to calculate with sufficient accuracy to probe the structure of the target nucleus. Only energy and momentum are transferred. Energy and charge are transferred between projectile and target. Some examples of this kind of reactions are: Usually at moderately low energy, one or more nucleons are transferred between the projectile and target. These are useful in studying outer shell structure of nuclei. Transfer reactions can occur: Examples: Reactions with neutrons are important in nuclear reactors and nuclear weapons . While
7200-663: The reactions produce far greater energy per unit of mass even though individual fission reactions are generally much more energetic than individual fusion ones, which are themselves millions of times more energetic than chemical reactions. Via the mass–energy equivalence , fusion yields a 0.7% efficiency of reactant mass into energy. This can be only be exceeded by the extreme cases of the accretion process involving neutron stars or black holes, approaching 40% efficiency, and antimatter annihilation at 100% efficiency. (The complete conversion of one gram of matter would release 9 × 10 joules of energy.) An important fusion process
7290-411: The remaining He nucleus is 3.5 MeV, so the total energy liberated is 17.6 MeV. This is many times more than what was needed to overcome the energy barrier. The reaction cross section (σ) is a measure of the probability of a fusion reaction as a function of the relative velocity of the two reactant nuclei. If the reactants have a distribution of velocities, e.g. a thermal distribution, then it
7380-417: The repulsive electrostatic force. This can also be described as the nuclei overcoming the so-called Coulomb barrier . The kinetic energy to achieve this can be lower than the barrier itself because of quantum tunneling. The Coulomb barrier is smallest for isotopes of hydrogen, as their nuclei contain only a single positive charge. A diproton is not stable, so neutrons must also be involved, ideally in such
7470-465: The resulting energy is released in an uncontrolled manner, as it is in thermonuclear weapons ("hydrogen bombs") and in most stars ; and controlled , where the fusion reactions take place in an environment allowing some or all of the energy released to be harnessed for constructive purposes. Temperature is a measure of the average kinetic energy of particles, so by heating the material it will gain energy. After reaching sufficient temperature, given by
7560-417: The same reason that the helium atom is inert: each pair of protons and neutrons in He-4 occupies a filled 1s nuclear orbital in the same way that the pair of electrons in the helium atom occupy a filled 1s electron orbital ). Consequently, alpha particles appear frequently on the right-hand side of nuclear reactions. The energy released in a nuclear reaction can appear mainly in one of three ways: When
7650-421: The size of iron, in the process of nuclear fission . Nuclear fission thus releases energy that has been stored, sometimes billions of years before, during stellar nucleosynthesis . Electrically charged particles (such as fuel ions) will follow magnetic field lines (see Guiding centre ). The fusion fuel can therefore be trapped using a strong magnetic field. A variety of magnetic configurations exist, including
7740-608: The supply of hydrogen is exhausted in their cores, their cores (or a shell around the core) start fusing helium to carbon . In the most massive stars (at least 8–11 solar masses ), the process is continued until some of their energy is produced by fusing lighter elements to iron . As iron has one of the highest binding energies , reactions producing heavier elements are generally endothermic . Therefore, significant amounts of heavier elements are not formed during stable periods of massive star evolution, but are formed in supernova explosions . Some lighter stars also form these elements in
7830-410: The toroidal geometries of tokamaks and stellarators and open-ended mirror confinement systems. A third confinement principle is to apply a rapid pulse of energy to a large part of the surface of a pellet of fusion fuel, causing it to simultaneously "implode" and heat to very high pressure and temperature. If the fuel is dense enough and hot enough, the fusion reaction rate will be high enough to burn
7920-469: Was a particularly remarkable development since at that time fusion and thermonuclear energy had not yet been discovered, nor even that stars are largely composed of hydrogen (see metallicity ). Eddington's paper reasoned that: All of these speculations were proven correct in the following decades. The primary source of solar energy, and that of similar size stars, is the fusion of hydrogen to form helium (the proton–proton chain reaction), which occurs at
8010-483: Was accomplished by Mark Oliphant in 1932. In the remainder of that decade, the theory of the main cycle of nuclear fusion in stars was worked out by Hans Bethe . Research into fusion for military purposes began in the early 1940s as part of the Manhattan Project . The first artificial thermonuclear fusion reaction occurred during the 1951 Greenhouse Item test of the first boosted fission weapon , which uses
8100-430: Was studied in detail by Steven Jones in the early 1980s. Net energy production from this reaction has been unsuccessful because of the high energy required to create muons , their short 2.2 μs half-life , and the high chance that a muon will bind to the new alpha particle and thus stop catalyzing fusion. Some other confinement principles have been investigated. The key problem in achieving thermonuclear fusion
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