Fusão aneutrônica: diferenças entre revisões

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{{em tradução|en:Aneutronic fusion|data=agosto de 2021}}
'''Fusão Aneutrônica''' é um tipo de [[fusão nuclear]] em que os [[nêutrons]] representam menos do que 1% das partículas energizadas resultantes da reação.<ref>http://www.njleg.state.nj.us/2006/Bills/A3000/2731_I1.HTM</ref> 80% das reações de fusão nuclear liberam energia em nêutrons. Fusões aneutrônicas bem sucedidas iriam reduzir muito os problemas associados com a [[radiação de neutrões|radiação de nêutrons]].
{{Imagem múltipla
| align = right
| header = Reações neutrônica e aneutrônica:
| header_background =
| footer = '''1:''' Fusão nuclear de deutério-trítio: reação neutrônica gerando energia, produzindo hélio e emitindo um nêutron. <br />'''2:''' Reação de fusão lítio-6 + deutério: reação aneutrônica, na qual a energia liberada é transportada por partículas alfa e não por nêutrons.
| image1 = Kernfusie dt reactie.png
| width1 = 209
| caption1 = <center>'''1'''</center>
| image2 = Li6-D Reaction.svg
| width2 = 190
| caption2 = <center>'''2''' </center>
}}
{{Física Nuclear}}
'''Fusão aneutrônica''' é qualquer forma de de [[fusão nuclear]] em que muito pouca [[energia]] liberada é transportada pelos [[nêutron]]s. Neste processo, os nêutrons representam menos do que 1% das partículas energizadas resultantes da reação.<ref>http://www.njleg.state.nj.us/2006/Bills/A3000/2731_I1.HTM</ref> Enquanto as reações de fusão nuclear de limiar mais baixo liberam até 80% de sua energia na forma de nêutrons, as reações aneutrônicas liberam energia na forma de partículas carregadas, normalmente [[próton]]s ou [[partículas alfa]]. A fusão aneutrônica bem-sucedida reduziria muito os problemas associados à [[Radiação de neutrões|radiação de nêutrons]], como [[radiação ionizante]] prejudicial, ativação de nêutrons e requisitos para proteção biológica, manuseio remoto e segurança.


Como é mais simples converter a energia de partículas carregadas em [[energia elétrica]] do que converter a energia de partículas não carregadas, uma reação aneutrônica seria atraente para sistemas de energia. Alguns proponentes veem um potencial para reduções dramáticas de [[custo]]s convertendo energia diretamente em eletricidade, bem como eliminando a radiação dos nêutrons, contra a qual é difícil proteger-se.<ref name="Principles of Fusion Energy: An Introduction to Fusion Energy for Students of Science and Engineering">Harms, A. A.; Schoepf, Klaus F.; Kingdon, David Ross (2000). [https://books.google.com.br/books?id=DD0sZgutqowC&pg=PA8&redir_esc=y#v=onepage&q&f=false ''Principles of Fusion Energy: An Introduction to Fusion Energy for Students of Science and Engineering'']. World Scientific, 2000, {{en}}, págs. 8-11. ISBN 9789812380333 Consultado em 5 de agosto de 2021.</ref><ref>Larry T. Cox Jr., Franklin B. Mead Jr. and Chan K. Choi Jr., (1990).[https://www.fulviofrisone.com/attachments/article/375/Thermonuclear%20Reaction%20Listing%20with%20Cross-Section%20Data%20for%204%20Advanced%20Reactions. ''Thermonuclear Reaction Listing with Cross-Section Data for Four Advanced Reactions''], Fusion Technology, Volume 18, no. 2. {{en}} Consultado em 5 de agosto de 2021.</ref> No entanto, as condições necessárias para aproveitar a fusão aneutrônica são muito mais extremas do que aquelas exigidas para a fusão [[deutério]]-[[trítio]] sendo investigada no [[ITER]].
== Referencias ==


== Reações possíveis ==
{{refs|2}}


Várias reações nucleares não produzem nêutrons em nenhum de seus ramos. Aquelas com as maiores seções de choque são estas:

{|
|+ Reações aneutrônicas de alta [[seção de choque]].<ref name="Principles of Fusion Energy: An Introduction to Fusion Energy for Students of Science and Engineering"/>
|-
! style=" background: #efefef;" | [[Isótopo]]s
! colspan="9" style="background: #efefef;" |Reação
|-
| [[Deutério]] - [[Hélio-3]]
|<sup>2</sup>D || + || <sup>3</sup>He
|→ || &nbsp; || [[Hélio-4|<sup>4</sup>He]] || + || <sup>1</sup>p || + 18.3 [[electronvolt|MeV]]
|-
| Deutério - [[Lítio|lítio-6]]
|<sup>2</sup>D || + || <sup>6</sup>Li
|→ || 2 || <sup>4</sup>He || &nbsp; || &nbsp; || + 22.4 MeV
|-
| [[Próton]] - Lítio-6
|<sup>1</sup>p || + || <sup>6</sup>Li
|→ || || <sup>4</sup>He || + || <sup>3</sup>He || + 4.0 MeV
|-
| Hélio-3 – Lítio-6
|<sup>3</sup>He || + || <sup>6</sup>Li
|→ || 2 || <sup>4</sup>He || + || <sup>1</sup>p || + 16.9 MeV
|-
| Hélio-3 - Hélio-3
|<sup>3</sup>He || + || <sup>3</sup>He
|→ || &nbsp; || <sup>4</sup>He ||| + || 2 <sup>1</sup>p || + 12.86 MeV
|-
| Próton – Lítio-7
|<sup>1</sup>p || + || <sup>7</sup>Li
|→ || 2 || <sup>4</sup>He || &nbsp; || &nbsp; || + 17.2 MeV
|-
| Próton – [[Boro]]-11
|<sup>1</sup>p || + || <sup>11</sup>B
|→ || 3 || <sup>4</sup>He || &nbsp; || &nbsp; || + 8.7 MeV
|-
| Próton – [[Nitrogênio]]
|<sup>1</sup>p || + || <sup>15</sup>N
|→ || &nbsp; || [[Carbono-12|<sup>12</sup>C]] || + || <sup>4</sup>He || + 5.0 MeV
|}
{{clr}}

<!------
{{short description|Any form of fusion power in which very little of the energy released is carried by neutrons}}
[[File:Li6-D Reaction.svg|thumb|[[Lithium-6]]–[[deuterium]] fusion reaction: an aneutronic fusion reaction, with energy released carried by [[alpha particles]], not neutrons.]]
'''Aneutronic fusion''' is any form of [[fusion power]] in which very little of the [[energy]] released is carried by neutrons. While the lowest-threshold [[Nuclear fusion#Important reactions|nuclear fusion reactions]] release up to 80% of their energy in the form of [[neutrons]], aneutronic reactions release energy in the form of charged particles, typically [[protons]] or [[alpha particles]]. Successful aneutronic fusion would greatly reduce problems associated with [[neutron radiation]] such as damaging [[ionizing radiation]], [[neutron activation]], and requirements for biological shielding, remote handling and safety.

Since it is simpler to convert the energy of charged particles into electrical power than it is to convert energy from uncharged particles, an aneutronic reaction would be attractive for power systems. Some proponents see a potential for dramatic cost reductions by converting energy directly to electricity, as well as in eliminating the radiation from neutrons, which are difficult to shield against.<ref name="HarmsSchoepf2000" /><ref>Larry T. Cox Jr., Franklin B. Mead Jr. and Chan K. Choi Jr., (1990). "Thermonuclear Reaction Listing with Cross-Section Data for Four Advanced Reactions"], ''Fusion Technology, Volume 18'', no. 2. Retrieved 2019-05-07.</ref> However, the conditions required to harness aneutronic fusion are much more extreme than those required for [[Deuterium-Tritium fusion|deuterium-tritium fusion]] being investigated in [[ITER]].

{{toclimit|3}}

== Candidate reactions ==

Several nuclear reactions produce no neutrons on any of their branches. Those with the largest [[Nuclear cross section|cross sections]] are these:

{|
|+ High nuclear cross section aneutronic reactions<ref name="HarmsSchoepf2000">{{cite book|first1=A. A. |last1=Harms|first2=Klaus F. |last2=Schoepf|first3=David Ross |last3=Kingdon|title=Principles of Fusion Energy: An Introduction to Fusion Energy for Students of Science and Engineering|url={{google books |plainurl=y |id=DD0sZgutqowC| page=8}} |year=2000|publisher=World Scientific|isbn=978-981-238-033-3| pages = 8–11 }}</ref>
|-
! style=" background: #efefef;" | Isotopes
! colspan="9" style="background: #efefef;" |Reaction
|-
| Deuterium - Helium-3
|[[deuterium|<sup>2</sup>D]] || + || [[helium-3|<sup>3</sup>He]]
|→ || &nbsp; || [[helium-4|<sup>4</sup>He]] || + || [[proton|<sup>1</sup>p]] || + 18.3 [[electronvolt|MeV]]
|-
| Deuterium - Lithium-6
|[[deuterium|<sup>2</sup>D]] || + || [[lithium-6|<sup>6</sup>Li]]
|→ || 2 || [[helium-4|<sup>4</sup>He]] || &nbsp; || &nbsp; || + 22.4 MeV
|-
| Proton - Lithium-6
|[[proton|<sup>1</sup>p]] || + || [[lithium-6|<sup>6</sup>Li]]
|→ || || [[helium-4|<sup>4</sup>He]] || + || [[helium-3|<sup>3</sup>He]] || + 4.0 MeV
|-
| Helium-3 – Lithium-6
|[[helium-3|<sup>3</sup>He]] || + || [[lithium-6|<sup>6</sup>Li]]
|→ || 2 || [[helium-4|<sup>4</sup>He]] || + || [[proton|<sup>1</sup>p]] || + 16.9 MeV
|-
| Helium-3 - Helium-3
|[[helium-3|<sup>3</sup>He]] || + || [[helium-3|<sup>3</sup>He]]
|→ || &nbsp; || [[helium-4|<sup>4</sup>He]] ||| + || 2 [[proton|<sup>1</sup>p]] || + 12.86 MeV
|-
| Proton – Lithium-7
|[[proton|<sup>1</sup>p]] || + || [[lithium-7|<sup>7</sup>Li]]
|→ || 2 || [[helium-4|<sup>4</sup>He]] || &nbsp; || &nbsp; || + 17.2 MeV
|-
| Proton – Boron-11
|[[proton|<sup>1</sup>p]] || + || [[boron-11|<sup>11</sup>B]]
|→ || 3 || [[helium-4|<sup>4</sup>He]] || &nbsp; || &nbsp; || + 8.7 MeV
|-
| Proton – Nitrogen
|[[proton|<sup>1</sup>p]] || + || [[nitrogen-15|<sup>15</sup>N]]
|→ || &nbsp; || [[Carbon-12|<sup>12</sup>C]] || + || [[helium-4|<sup>4</sup>He]] || + 5.0 MeV
|}

== Definition ==

Fusion reactions can be categorized by the '''neutronicity''' of the reaction, the fraction of the fusion energy released as neutrons. This is an important indicator of the magnitude of the problems associated with neutrons like radiation damage, biological shielding, remote handling, and safety.
The State of New Jersey has defined an aneutronic reaction as one in which neutrons carry no more than 1% of the total released energy,<ref>{{cite web|url=http://www.njleg.state.nj.us/2006/Bills/A3000/2731_I1.HTM |volume=A2731 |title = Assembly, No. 2731, State of New Jersey, 212th legislature|date = March 2, 2006|publisher=Njleg.state.nj.us |access-date=2012-04-01}}</ref> although many papers on aneutronic fusion<ref name=Roth>J. Reece Roth (1989). [https://www.tandfonline.com/doi/pdf/10.13182/FST89-A11963080 "Space Applications of Fusion Energy"], ''Fusion Technology, Volume 15'', no. 3. Retrieved 2019-05-07.</ref> include reactions that do not meet this criterion.

=== Reaction rates ===
The difficulty of a fusion reaction is characterized by the energy required for the nuclei to overcome their mutual electrostatic repulsion, the so-called [[Coulomb barrier]]. This is a function of the total electrical charge of the fuel ions, and is thus minimized for those ions with the lowest number of [[protons]]. Countering the electrostatic repulsion is the [[nuclear force]], which increases with the number of nucleons.

In most fusion reactor concepts, the energy needed to overcome the Coulomb barrier is provided by collisions with other fuel ions. In a thermalized fluid like a plasma, the [[temperature]] corresponds to an energy spectrum according to the [[Maxwell–Boltzmann distribution]]. Gasses in this state will have a population of particles with very high energy even if the bulk of the gas has an average energy much lower. Fusion devices rely on this distribution; even at bulk temperatures far below the Coulomb barrier energy, the energy released by the reactions is so great that capturing some of that back in the fuel will cause the population of high-energy ions within it to be high enough to keep the reaction going.

Thus, steady operation of the reactor is based on a balance between the rate that energy is added to the fuel by the fusion reactions and the rate energy is lost to the surroundings through a wide variety of processes. This concept is best expressed as the [[fusion triple product]], the product of the temperature, density and "confinement time", the amount of time energy remains in the fuel before escaping to the environment. The product of temperature and density gives the reaction rate for any given fuel. The rate of reaction is proportional to the [[nuclear cross section]] ("σ").<ref name="HarmsSchoepf2000" /><ref name=Feldbacher1988>Rainer Feldbacher and Manfred Heindler (1 August 1988). "Basic cross section data for aneutronic reactor", ''Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Volume 271,'' No 1, pp 55-64. [https://www.sciencedirect.com/science/article/pii/0168900288911254 DOI: 10.1016/0168-9002(88)91125-4].</ref>

Any given fusion device has a maximum plasma pressure it can sustain, and an economical device would always operate near this maximum. Given this pressure, the largest fusion output is obtained when the temperature is chosen so that <nowiki><σv></nowiki>/T<sup>2</sup> is a maximum. This is also the temperature at which the value of the triple product ''nT''τ required for ignition is a minimum, since that required value is inversely proportional to <nowiki><σv></nowiki>/T<sup>2</sup> (see [[Lawson criterion]]). A plasma is "ignited" if the fusion reactions produce enough power to maintain the temperature without external heating.

Because the Coulomb barrier is a product of the number of nucleons in the fuel ions, varieties of heavy hydrogen, [[deuterium]] and [[tritium]] (D-T), give the fuel with the lowest total Coulomb barrier. All other potential fuels will have higher Coulomb barrier, and thus require higher operational temperatures. Additionally, D-T fuels have the highest nuclear cross-sections, which means the reaction rates will be higher than any other fuel. This means that [[D-T fusion]] is the easiest to achieve, and one can compare the potential of other fuels by comparing it to the D-T reaction. The table below shows the ignition temperature and cross-section for three of the candidate aneutronic reactions, compared to D-T:

{| class="wikitable" style="margin:auto;"
|-
!Reaction !! Ignition<br>''T'' [keV] !! <nowiki><σv></nowiki>/T<sup>2</sup> [m<sup>3</sup>/s/keV<sup>2</sup>]
|-
|{{nuclide|deuterium}}-{{nuclide|tritium}} || 13.6 || 1.24×10<sup>−24</sup>
|-
|{{nuclide|deuterium}}-{{nuclide|helium|3}} || 58 || 2.24×10<sup>−26</sup>
|-
|p<sup>+</sup>-{{nuclide|lithium|6}} || 66 || 1.46×10<sup>−27</sup>
|-
|p<sup>+</sup>-{{nuclide|boron|11}} || 123 || 3.01×10<sup>−27</sup>
|}

As can be seen, the easiest to ignite of the aneutronic reactions, D-<sup>3</sup>He, has an ignition temperature over four times as high as that of the D-T reaction, and correspondingly lower cross-sections, while the p-<sup>11</sup>B reaction is nearly ten times more difficult to ignite.

== Technical challenges ==
Many challenges remain prior to the commercialization of aneutronic processes.

=== Temperature ===
The large majority of fusion research has gone toward D-T fusion, which is the easiest to achieve. Although the first experiments in the field started in 1939, and serious efforts have been continual since the early 1950s, {{asof|2020|lc=yes}} we are still many years away from achieving [[Fusion energy gain factor|breakeven]] using even this fuel. Fusion experiments typically use [[Deuterium-deuterium fusion]] (D-D) because deuterium is cheap and easy to handle, being non-radioactive. Performing experiments on D-T fusion is more difficult because tritium is expensive and radioactive, with additional environmental protection and safety measures.

The combination of lower cross-section and higher loss rates in D-He3 fusion is offset to a degree by the reactants being mainly charged particles that deposit their energy back in the plasma. This combination of offsetting features demands an operating temperature about four times that of a D-T system. However, due to the high loss rates and consequent rapid cycling of energy, the confinement time of a working reactor needs to be about fifty times higher than D-T, and the energy density about 80 times higher. This requires significant advances in plasma physics.<ref name=he3>{{cite journal |journal=Zeitschrift für Naturforschung |volume=70 |issue=2 |first1=Seyed Mohammad |last1=Motevalli |first2=Fereshteh |last2=Fadaei |doi=10.1515/zna-2014-0134 |date=7 February 2015 |title=A Comparison Between the Burn Condition of Deuterium–Tritium and Deuterium–Helium-3 Reaction and Stability Limits |url=https://www.degruyter.com/view/journals/zna/70/2/article-p79.xml?language=en}}</ref>

Proton–boron fusion requires ion energies, and thus plasma temperatures, almost ten times higher than those for D-T fusion. For any given density of the reacting nuclei, the reaction rate for proton-boron achieves its peak rate at around 600 [[keV]] (6.6 billion degrees Celsius or 6.6 [[gigakelvin]]s)<ref>{{Cite arXiv|eprint=0710.3149 |title=Advances towards pB11 Fusion with the Dense Plasma Focus |date=2007-10-16 |last1= Lerner |first1=Eric J. |last2= Terry |first2=Robert E. |class=physics.plasm-ph }}</ref> while D-T has a peak at around 66 keV (765 million degrees Celsius, or 0.765 gigakelvin). For pressure-limited confinement concepts, optimum [[operating temperature]]s are about 5 times lower, but the ratio is still roughly ten-to-one.

=== Power balance ===
The peak reaction rate of p–<sup>11</sup>B is only one third that for D-T, requiring better plasma confinement. Confinement is usually characterized by the time τ the energy must be retained so that the fusion power released exceeds the power required to heat the plasma. Various requirements can be derived, most commonly the product of the density, ''n''τ, and the product with the pressure ''nT''τ, both of which are called the [[Lawson criterion]]. The ''n''τ required for p–<sup>11</sup>B is 45 times higher than that for D-T. The ''nT''τ required is 500 times higher.<ref>Both figures assume the electrons have the same temperature as the ions. If operation with cold electrons is possible, as discussed below, the relative disadvantage of p–<sup>11</sup>B would be a factor of three smaller, as calculated [[Lawson criterion#note-0|here]].</ref> (See also [[Nuclear fusion#Neutronicity, confinement requirement, and power density|neutronicity, confinement requirement, and power density]].) Since the confinement properties of conventional fusion approaches, such as the [[tokamak]] and [[laser fusion|laser pellet fusion]] are marginal, most aneutronic proposals use radically different confinement concepts.

In most fusion plasmas, [[bremsstrahlung]] radiation is a major energy loss channel. (See also [[Nuclear fusion#Bremsstrahlung losses in quasineutral, isotropic plasmas|bremsstrahlung losses in quasineutral, isotropic plasmas]].) For the p–<sup>11</sup>B reaction, some calculations indicate that the [[bremsstrahlung]] power will be at least 1.74 times larger than the fusion power. The corresponding ratio for the <sup>3</sup>He-<sup>3</sup>He reaction is only slightly more favorable at 1.39. This is not applicable to non-neutral plasmas, and different in anisotropic plasmas.

In conventional reactor designs, whether based on [[magnetic confinement fusion|magnetic]] or [[inertial confinement fusion|inertial confinement]], the bremsstrahlung can easily escape the plasma and is considered a pure energy loss term. The outlook would be more favorable if the plasma could reabsorb the radiation. Absorption occurs primarily via [[Thomson scattering]] on the [[electrons]],<ref>[http://www.astro.utu.fi/~cflynn/astroII/l3.html Lecture 3 : Accelerated charges and bremsstrahlung], lecture notes in astrophysics from Chris Flynn, Tuorla Observatory</ref> which has a total cross section of σ<sub>T</sub> = 6.65×10<sup>−29</sup> m². In a 50–50 D-T mixture this corresponds to a range of 6.3 g/cm².<ref>m<sub>i</sub>/σ<sub>T</sub> = 2.5×(1.67×10<sup>−24</sup> g)/(6.65×10<sup>−25</sup> cm²) = 6.28 g/cm²</ref> This is considerably higher than the Lawson criterion of ρ''R'' > 1&nbsp;g/cm², which is already difficult to attain, but might be achievable in inertial confinement systems.<ref>Robert W. B. Best. "Advanced Fusion Fuel Cycles". Fusion Technology, Vol. 17 (July 1990), pp. 661–5.</ref>

In [[megatesla]] magnetic fields a [[quantum mechanics|quantum mechanical]] effect might suppress energy transfer from the ions to the electrons.<ref>G.S. Miller, E.E. Salpeter, and I. Wasserman, Deceleration of infalling plasma in the atmospheres of accreting neutron stars. I. Isothermal atmospheres, ''Astrophysical Journal'', '''314''': 215–233, 1987 March 1. In one case, they report an increase in the stopping length by a factor of 12.</ref> According to one calculation,<ref name=autogenerated1>E.J. Lerner, Prospects for p11B fusion with the Dense Plasma Focus: New Results (Proceedings of the Fifth Symposium on Current Trends in International Fusion Research), 2002, https://arxiv.org/abs/physics/0401126</ref> bremsstrahlung losses could be reduced to half the fusion power or less. In a strong magnetic field [[cyclotron radiation]] is even larger than the bremsstrahlung. In a megatesla field, an electron would lose its energy to cyclotron radiation in a few picoseconds if the radiation could escape. However, in a sufficiently dense plasma (''n''<sub>e</sub> &gt; 2.5×10<sup>30</sup> m<sup>−3</sup>, a density greater than that of a solid<ref>Assuming 1 MT field strength. This is several times higher than solid density.</ref>), the [[cyclotron frequency]] is less than twice the [[plasma frequency]]. In this well-known case, the cyclotron radiation is trapped inside the plasmoid and cannot escape, except from a very thin surface layer.

While megatesla fields have not yet been achieved, fields of 0.3 megatesla have been produced with high intensity lasers,<ref>[http://jasmine.kues.kyoto-u.ac.jp/pps/PPSProceedings/05_Beiersdorfer_LaserPPS.pdf "X-ray Polarization Measurements at Relativistic Laser Intensities"] {{webarchive |url=https://web.archive.org/web/20070721025426/http://jasmine.kues.kyoto-u.ac.jp/pps/PPSProceedings/05_Beiersdorfer_LaserPPS.pdf |date=July 21, 2007 }}, P. Beiersdorfer, ''et al.''</ref> and fields of 0.02–0.04 megatesla have been observed with the [[dense plasma focus]] device.<ref>Bostick, W.H. et al., ''Ann. NY Acad. Sci.'', 251, 2 (1975)</ref><ref>The magnetic pressure at 1 MT would be 4×10<sup>11</sup> [[Pascal (unit)|MPa]]. For comparison, the [[tensile strength]] of [[stainless steel]] is typically 600 MPa.</ref>

At much higher densities (''n''<sub>e</sub> &gt; 6.7×10<sup>34</sup> m<sup>−3</sup>), the electrons will be [[Electron-degenerate matter|Fermi degenerate]], which suppresses bremsstrahlung losses, both directly and by reducing energy transfer from the ions to the electrons.<ref>{{cite journal | last1 = Son | first1 = S. | last2 = Fisch | first2 = N.J. | year = 2004 | title = Aneutronic fusion in a degenerate plasma | url = http://w3.pppl.gov/~fisch/fischpapers/2004/Son_PLA_04.pdf | journal = Physics Letters A | volume = 329 | issue = 1–2| pages = 76–82 | doi=10.1016/j.physleta.2004.06.054|bibcode = 2004PhLA..329...76S }}</ref> If necessary conditions can be attained, net energy production from p–<sup>11</sup>B or D–<sup>3</sup>He fuel may be possible. The probability of a feasible reactor based solely on this effect remains low, however, because the [[fusion energy gain factor|gain]] is predicted to be less than 20, while more than 200 is usually considered to be necessary.

=== Power density ===

In every published fusion power plant design, the part of the plant that produces the fusion reactions is much more expensive than the part that converts the nuclear power to electricity. In that case, as indeed in most power systems, power density is an important characteristic.<ref>Comparing two different types of power systems involves many factors in addition to the power density. Two of the most important are the volume in which energy is produced in comparison to the total volume of the device, and the cost and complexity of the device. In contrast, the comparison of two different fuel cycles in the same type of machine is generally much more robust.</ref> Doubling power density at least halves the cost of electricity. In addition, the confinement time required depends on the power density.

It is, however, not trivial to compare the power density produced by different fusion fuel cycles. The case most favorable to p–<sup>11</sup>B relative to D-T fuel is a (hypothetical) confinement device that only works well at ion temperatures above about 400 keV, in which the reaction rate parameter <σ''v''> is equal for the two fuels, and that runs with low electron temperature. p–<sup>11</sup>B does not require as long a confinement time because the energy of its charged products is two and a half times higher than that for D-T. However, relaxing these assumptions, for example by considering hot electrons, by allowing the D-T reaction to run at a lower temperature or by including the energy of the neutrons in the calculation shifts the power density advantage to D-T.

The most common assumption is to compare power densities at the same pressure, choosing the ion temperature for each reaction to maximize power density, and with the electron temperature equal to the ion temperature. Although confinement schemes can be and sometimes are limited by other factors, most well-investigated schemes have some kind of pressure limit. Under these assumptions, the power density for p–<sup>11</sup>B is about 2,100 times smaller than that for D-T. Using cold electrons lowers the ratio to about 700. These numbers are another indication that aneutronic fusion power is not possible with mainline confinement concepts.

== Research{{Anchor|Companies}}==
* [[Lawrenceville Plasma Physics]] has published initial results and outlined a theory and experimental program for aneutronic fusion with the [[Dense Plasma Focus]] (DPF)<ref>{{cite journal | title= Theory and Experimental Program for p-B11 Fusion with the Dense Plasma Focus
| date= January 28, 2011 | journal= [[Journal of Fusion Energy]]
| doi=10.1007/s10894-011-9385-4 | volume=30 | issue= 5
| pages=367–376|bibcode = 2011JFuE...30..367L | last1 = Lerner | first1 = Eric J.}}</ref><ref>{{Cite web|url=http://video.google.com/videoplay?docid=-1518007279479871760&q=Google+tech+talks+lerner&pr=goog-sl|title=Focus Fusion: The Fastest Route to Cheap, Clean Energy}}</ref> The private effort was initially funded by NASA's [[Jet Propulsion Laboratory]].<ref>JPL Contract 959962, JPL Contract 959962</ref> Support for other DPF aneutronic fusion investigations came from the [[Air Force Research Laboratory]].<ref>{{Cite web|url=http://focusfusion.org/index.php/site/article/university_of_illinois_space_propulsion/|archiveurl=https://web.archive.org/web/20110126033301/http://focusfusion.org/index.php/site/article/university_of_illinois_space_propulsion/|url-status=dead|title=University of Illinois Space Propulsion|archivedate=January 26, 2011}}</ref>
* [[Polywell]] fusion was pioneered by the late [[Robert W. Bussard]] and funded by the [[United States Navy|US Navy]], uses [[inertial electrostatic confinement]]. Research continues at the company he founded, EMC2.<ref>Bussard, R. W. & Jameson L. W., [http://www.aiaa.org/content.cfm?pageid=406&gTable=japaperimportPre97&gID=51434 Inertial-Electrostatic-Fusion Propulsion Spectrum: Air-Breathing to Interstellar Flight] {{webarchive|url=https://web.archive.org/web/20070930183543/http://www.aiaa.org/content.cfm?pageid=406&gTable=japaperimportPre97&gID=51434 |date=2007-09-30 }}, ''Journal of Propulsion and Power'' Vol. 11, No. 2, March–April 1995</ref><ref>[http://video.google.com/videoplay?docid=1996321846673788606 Should Google go Nuclear?] – A video of Dr. Bussard presenting his concept to an audience at Google</ref>
* [[Tri Alpha Energy, Inc.]] is pursuing aneutronic fusion in the Colliding Beam Fusion Reactor (CBFR) based on electromagnetic heating, acceleration, collision and merging of two [[compact toroid]]s in [[Field-Reversed Configuration]] at supersonic speeds.<ref>{{cite journal |last1=Rostoker |first1=Norman |last2=Binderbauer |first2=Michl W. |last3=Monkhorst |first3=Hendrik J. |date=21 November 1997 |title=Colliding Beam Fusion Reactor
|journal=Science |publisher=American Association for the Advancement of Science |volume=278 |issue=5342 |pages=1419–1422 |doi=10.1126/science.278.5342.1419 |bibcode=1997Sci...278.1419R |pmid=9367946
}}</ref><ref>{{cite conference |url=http://www.iccworkshops.org/icc2011/uploads/241/icc2011_gota_talk_8_16_11.pdf |title=A Well-Confined Field-Reversed Configuration Plasma Formed by Dynamic Merging of Two Colliding Compact Toroids in C-2 |last1=Gota |first1=Hiroshi |last2=Binderbauer |first2=Michl W. |last3=Guo |first3=Houyang Y. |last4=Tuszewski |first4=Michel |author5=the TAE Team |conference=Innovative Confinement Concepts (ICC) & US-Japan Compact Torus Plasma (CT) Workshops |date=16 August 2011 |publisher=University of Washington |location=Seattle, WA |access-date=17 May 2014}}</ref><ref>{{cite conference|url= http://www.int.washington.edu/talks/WorkShops/int_12_3/People/Weller_H/Weller.pdf |title=Tri-Alpha structures in 12C |last=Weller |first=Henry R. |conference=Light Nuclei from First Principles Workshop |date= 10 October 2012
|publisher=University of Washington |location=Institute for Nuclear Theory |access-date=16 May 2014}}</ref>
* The [[Z Pulsed Power Facility|Z-machine]] at [[Sandia National Laboratory]], a [[z-pinch]] device, can produce ion energies of interest to hydrogen–boron reactions, up to 300 keV.<ref>Malcolm Haines et al., Viscous Heating of Ions through Saturated Fine-Scale MHD Instabilities in a Z-Pinch at 200–300 keV Temperature; Phys. Rev. Lett. 96, 075003 (2006)</ref> Non-equilibrium plasmas usually have an electron temperature higher than their ion temperature, but the plasma in the Z machine has a special, reverted non-equilibrium state, in which the ''ion temperature is 100 times higher than electron temperature''. These data represent a new research field, and indicate that Bremsstrahlung losses could be in fact lower than previously expected in such a design.
* ''HB11 Energy'', an Australian [[University spin-off|spin-off company]] created in September 2017.<ref name="HB11 Energy website">{{cite web
|url=https://www.hb11.energy |title=hb11.energy |website=HB11 Energy website
}}</ref> It develops a dual [[chirped pulse amplification]]<ref>{{Cite web|url=https://newatlas.com/energy/hb11-hydrogen-boron-fusion-clean-energy/|title=Radical hydrogen-boron reactor leapfrogs current nuclear fusion tech|last=Blain|first=Loz|date=February 21, 2020|website=New Atlas|language=en-US|access-date=2020-02-22}}</ref> laser driven proton-boron technique with an avalanche reaction offering a billion time increased fusion yield improvement compared to other previous [[inertial confinement fusion]] systems. It holds the patents of [[University of New South Wales|UNSW]]'s theoretical physicist [[Heinrich Hora]].<ref>{{cite journal |last1=Hora |first1=H. |last2=Eliezer |first2=S. |last3=Kirchhoff |first3=G.J. |last4=Nissim |first4=N. |last5=Wang |first5=J.X. |last6=Lalousis |first6=P. |last7=Xu |first7=Y.X. |last8=Miley |first8=G.H. |last9=Martinez-Val |first9=J.M. |last10=McKenzie |first10=W. |last11=Kirchhoff |first11=J. |display-authors=3 |title=Road map to clean energy using laser beam ignition of boron-hydrogen fusion |date=12 December 2017 |journal=Laser and Particle Beams |volume=35 |issue=4 |pages=730–740 |doi=10.1017/S0263034617000799|bibcode=2017LPB....35..730H |doi-access=free }}</ref><ref>{{cite web |author=Brian Wang |date=13 December 2017 |website=NextBigFuture |title=Breakthroughs could make commercial laser nuclear fusion through billion times improvements in yield |url=https://www.nextbigfuture.com/2017/12/billion-times-improvement-with-laser-nuclear-fusion-using-avalanche-reaction-effect.html}}</ref><ref>{{cite news |author=Wilson Da Silva |date=14 December 2017 |title=Laser-boron fusion now 'leading contender' for energy |work=UNSW Newsroom |url=https://newsroom.unsw.edu.au/news/science-tech/laser-boron-fusion-now-‘leading-contender’-energy}}</ref>
None of these efforts has yet tested its device with hydrogen–boron fuel, so the anticipated performance is based on extrapolating from theory, experimental results with other fuels and from simulations.
* A picosecond pulse of a 10-terawatt laser produced hydrogen–boron aneutronic fusions for a Russian team in 2005.<ref>{{cite journal | last1 = Belyaev | first1 = V.S. |display-authors=et al | year = 2005 | title = Observation of neutronless fusion reactions in picosecond laser plasmas | url = http://fire.pppl.gov/fusion_pb11_belyaev_082605.pdf | journal = Physical Review E | volume = 72 | issue = 2| pages = 026406 | doi = 10.1103/physreve.72.026406| pmid = 16196717 | bibcode = 2005PhRvE..72b6406B }}, mentioned in news@nature.com on August 26, 2005 : [http://fire.pppl.gov/fusion_lasers_nature_082605.pdf Lasers trigger cleaner fusion]</ref> However, the number of the resulting α particles (around 10<sup>3</sup> per laser pulse) was low.
* A French research team [https://web.archive.org/web/20141202062802/http://www.fusenet.eu/node/575 fused protons and boron-11 nuclei using a laser-accelerated proton beam and high-intensity laser pulse]. In October 2013 they reported an estimated 80 million fusion&nbsp;reactions during a 1.5 nanosecond laser pulse.<ref>{{Cite web|url=http://www.fusenet.eu/node/575|title=Record proton-boron fusion rate achieved {{!}} FuseNet|website=www.fusenet.eu|access-date=2016-10-11|archive-url=https://web.archive.org/web/20141202062802/http://www.fusenet.eu/node/575|archive-date=2014-12-02|url-status=dead}}</ref>
* In 2016, a team at the Shanghai [[Chinese Academy of Sciences]] produced a laser pulse of 5.3 petawatts with the ''Superintense Ultrafast Laser Facility'' (SULF) and would be able to reach 10 petawatts with the same equipment. The team is now building a 100-petawatt laser, the ''Station of Extreme Light'' (SEL) planned to be operational by 2023. It would be able to produce antiparticles ([[pair production|electron-positron pairs]]) out of the [[vacuum]]. A similar European project also exists for the same timeframe, a 200-PW laser known as the [[Extreme Light Infrastructure]] (ELI). Although these two projects do not currently involve aneutronic fusion research, they show how aneutronic nuclear energy could benefit from the race toward exawatt ([[Orders of magnitude (numbers)#1018|10<sup>18</sup>]] W) and even zettawatt ([[Orders of magnitude (numbers)#1021|10<sup>21</sup>]] W) lasers.<ref>{{cite web |author=Biran Wang |website=NextBigFuture |date=2 February 2018 |title=100 Petawatt lasers could generate antimatter from vacuum and create commercial nuclear fusion |url=https://www.nextbigfuture.com/2018/02/100-petawatt-lasers-could-generate-antimatter-from-vacuum-and-create-commercial-nuclear-fusion.html}}</ref>

== Candidate fuels==

=== Helium-3 ===
{{see also|helium-3}}
The <sup>3</sup>He–D reaction has been studied as an alternative fusion plasma because it is the fuel with the lowest energy threshold for aneutronic fusion reaction.

The p–<sup>6</sup>Li, <sup>3</sup>He–<sup>7</sup>Li, and <sup>3</sup>He–<sup>3</sup>He reaction rates are not particularly high in a thermal plasma. When treated as a chain, however, they offer the possibility of enhanced reactivity due to a [[Distribution function (physics)|non-thermal distribution]]. The product <sup>3</sup>He from the p–<sup>6</sup>Li reaction could participate in the second reaction before thermalizing, and the product p from <sup>3</sup>He–<sup>7</sup>Li could participate in the former before thermalizing. Detailed analyses, however, do not show sufficient reactivity enhancement to overcome the inherently low cross section.{{citation needed|date=December 2013}}

The <sup>3</sup>He reaction suffers from a helium-3 availability problem. Helium-3 occurs in only minuscule amounts naturally on Earth, so it would either have to be bred from neutron reactions (counteracting the potential advantage of aneutronic fusion) or mined from extraterrestrial sources.

The amount of helium-3 fuel needed for large-scale applications can also be described in terms of total consumption: according to the [[Energy Information Administration|US Energy Information Administration]], "Electricity consumption by 107 million U.S. households in 2001 totaled 1,140 billion&nbsp;kW·h" ({{val|1.14|e=15|u=W·h}}). Again assuming 100% conversion efficiency, 6.7 tonnes per year of helium-3 would be required for that segment of the energy demand of the United States, 15 to 20 tonnes per year given a more realistic end-to-end conversion efficiency. Extracting that amount of pure helium-3 would entail processing 2 billion tonnes of lunar material per year, even assuming a recovery rate of 100%.{{Citation needed|date=July 2021}}

=== Deuterium ===
Although the deuterium reactions (deuterium + helium-3 and deuterium + lithium-6) do not in themselves release neutrons, in a fusion reactor the plasma would also produce D-D side reactions that result in reaction product of helium-3 plus a neutron. Although neutron production can be minimized by running a plasma reaction hot and deuterium-lean, the fraction of energy released as neutrons is probably several percent, so that these fuel cycles, although neutron-poor, do not meet the 1% threshold. See [[Helium-3#Fusion reactions|Helium-3]]. The D-<sup>3</sup>He reaction also suffers from the <sup>3</sup>He fuel availability problem, as discussed above.

===Lithium===
Fusion reactions involving lithium are well studied due to the use of lithium for breeding tritium in [[thermonuclear weapon]]s. They are intermediate in ignition difficulty between the reactions involving lower atomic-number species, H and He, and the <sup>11</sup>B reaction.

The p–<sup>7</sup>Li reaction, although highly energetic, releases neutrons because of the high cross section for the alternate neutron-producing reaction <sup>1</sup>p + <sup>7</sup>Li
→ [[Beryllium|<sup>7</sup>Be]] + n
<ref>S. G. Mashnik, M. B. Chadwick, H. G. Hughes, R. C. Little, R. E. MacFarlane, L. S. Waters, and P. G. Young, "7Li(p,n) NUCLEAR DATA LIBRARY FOR INCIDENT PROTON ENERGIES TO 150 MEV", Feb. 8, 2008. [https://arxiv.org/abs/nucl-th/0011066 ArXiv] (retrieved 17 January 2017)</ref>

=== Boron ===
Many studies of aneutronic fusion concentrate on the reaction p–<sup>11</sup>B,<ref>{{cite journal | first = W. M. | last = Nevins | title = A Review of Confinement Requirements for Advanced Fuels | journal = Journal of Fusion Energy | volume = 17 | issue = 1 | date = 1998 | doi = 10.1023/A:1022513215080 | pages = 25–32|bibcode = 1998JFuE...17...25N}}</ref><ref>{{cite news | url = https://www.independent.co.uk/news/science/fusion-breakthrough-a-magic-bullet-for-energy-crisis-1864275.html | title = Fusion breakthrough a magic bullet for energy crisis? | work=The Independent | location=London | first=Pat | last=Pilcher | date=2010-01-11 | access-date=2010-04-25}}</ref> which uses relatively easily available fuel. The fusion of the boron nucleus with a proton produces energetic alpha particles (helium nuclei).

Since the ignition of the p–<sup>11</sup>B reaction is much more difficult than the D-T reaction studied in most fusion programs, alternatives to the usual [[tokamak]] fusion reactors are usually proposed, such as laser [[inertial confinement fusion]].<ref name=":0">{{Cite news|url=https://www.zmescience.com/science/hydrogen-boron-laser-fusion-15122017|title=Functional hydrogen-boron fusion could be here "within the next decade", powered by huge lasers|date=2017-12-15|work=ZME Science|access-date=2017-12-16|language=en-US}}</ref> One proposed method uses one laser to create a boron-11 [[plasma (physics)|plasma]] and another to create a stream of protons that smash into the plasma. The proton beam produces a tenfold increase of boron fusion because protons and boron nuclei collide directly. Earlier methods used a solid boron target, "protected" by its electrons, which reduced the fusion rate.<ref name="nat1013">{{Cite journal|date=2013|title=Two-laser boron fusion lights the way to radiation-free energy|journal=Nature|doi=10.1038/nature.2013.13914|last1=Cowen|first1=R.}}</ref> Experiments suggest that a petawatt-scale laser pulse could launch an ‘avalanche’ fusion reaction,<ref name=":0" /><ref>{{Cite journal|last=Hora|first=H.|last2=Eliezer|first2=S.|last3=Kirchhoff|first3=G. J.|last4=Nissim|first4=N.|last5=Wang|first5=J. X.|last6=Lalousis|first6=P.|last7=Xu|first7=Y. X.|last8=Miley|first8=G. H.|last9=Martinez-Val|first9=J. M.|date=December 2017|title=Road map to clean energy using laser beam ignition of boron-hydrogen fusion|journal=Laser and Particle Beams|volume=35|issue=4|pages=730–740|doi=10.1017/s0263034617000799|issn=0263-0346|bibcode=2017LPB....35..730H|doi-access=free}}</ref> although this remains controversial.<ref>{{cite journal |last1=Belloni |first1=F. |last2=Margarone |first2=D. |last3=Picciotto |first3=A. |last4=Schillaci |first4=F. |last5=Giuffrida |first5=L. |title=On the enhancement of p-11B fusion reaction rate in laser-driven plasma by α → p collisional energy transfer |journal=Physics of Plasmas |date=February 2018 |volume=25 |issue=2 |page=020701 |doi=10.1063/1.5007923 }}</ref> The plasma lasts about one [[nanosecond]], requiring the [[picosecond]] pulse of protons to be precisely synchronized. Unlike conventional methods, this approach does not require a magnetically confined plasma. The proton beam is preceded by an electron beam, generated by the same laser, that pushes away electrons in the boron plasma, allowing the protons more of a chance to collide with the boron nuclei and fuse.<ref name="nat1013" />

==== Residual radiation ====

Calculations show that at least 0.1% of the reactions in a thermal p–<sup>11</sup>B plasma produce neutrons, and the energy of these neutrons accounts for less than 0.2% of the total energy released.<ref>Heindler and Kernbichler, Proc. 5th Intl. Conf. on Emerging Nuclear Energy Systems, 1989, pp. 177–82. Even though 0.1% is a small fraction, the dose rate is still high enough to require very good shielding, as illustrated by the following calculation. Assume we have a very small reactor producing 30 kW of total fusion power (a full-scale power reactor might produce 100,000 times more than this) and 30 W in the form of neutrons. If there is no significant shielding, a worker in the next room, 10&nbsp;m away, might intercept (0.5 m<sup>2</sup>)/(4 pi (10&nbsp;m)<sup>2</sup>) = 4×10<sup>−4</sup> of this power, i.e., 0.012 W. With 70&nbsp;kg body mass and the definition 1 [[Gray (unit)|gray]] = 1 J/kg, we find a dose rate of 0.00017 Gy/s. Using a quality factor of 20 for fast neutrons, this is equivalent to 3.4 [[millisievert]]s. The maximum yearly occupational dose of 50 mSv will be reached in 15 s, the fatal ({{LD50}}) dose of 5 Sv will be reached in half an hour. If very effective precautions are not taken, the neutrons would also activate the structure so that remote maintenance and [[High-level radioactive waste management|radioactive waste disposal]] would be necessary.</ref>

These neutrons come primarily from the reaction:<ref>W. Kernbichler, R. Feldbacher, M. Heindler. "Parametric Analysis of p–<sup>11</sup>B as Advanced Reactor Fuel" in Plasma Physics and Controlled Nuclear Fusion Research (Proc. 10th Int. Conf., London, 1984) IAEA-CN-44/I-I-6. Vol. 3 (IAEA, Vienna, 1987).</ref>

:<sup>11</sup>B + [[Alpha particle|α]] → <sup>14</sup>N + n + 157 keV

The reaction itself produces only 157 keV, but the neutron carries a large fraction of the alpha energy, close to ''E''<sub>fusion</sub>/3 = 2.9 [[MeV]]. Another significant source of neutrons is:

:<sup>11</sup>B + p → [[Carbon-11|<sup>11</sup>C]] + n − 2.8 MeV.

These neutrons are less energetic, with an energy comparable to the fuel temperature. In addition, [[Carbon-11|<sup>11</sup>C]] itself is radioactive, but quickly decays to <sup>11</sup>B with a half life of only 20 minutes.

Since these reactions involve the reactants and products of the primary fusion reaction, it would be difficult to further lower the neutron production by a significant fraction. A clever magnetic confinement scheme could in principle suppress the first reaction by extracting the alphas as soon as they are created, but then their energy would not be available to keep the plasma hot. The second reaction could in principle be suppressed relative to the desired fusion by removing the high energy tail of the ion distribution, but this would probably be prohibited by the power required to prevent the distribution from thermalizing.

In addition to neutrons, large quantities of hard [[X-ray]]s are produced by [[bremsstrahlung]], and 4, 12, and 16 MeV [[gamma ray]]s are produced by the fusion reaction

:<sup>11</sup>B + p → [[carbon-12|<sup>12</sup>C]] + [[Gamma ray|γ]] + 16.0 MeV

with a branching probability relative to the primary fusion reaction of about 10<sup>−4</sup>.<ref>As with the neutron dose, shielding is essential with this level of gamma radiation. The neutron calculation in the previous note would apply if the production rate is decreased a factor of ten and the quality factor is reduced from 20 to 1. Without shielding, the occupational dose from a small (30 kW) reactor would still be reached in about an hour.</ref>

The hydrogen must be [[Isotope separation|isotopically pure]] and the influx of impurities into the plasma must be controlled to prevent neutron-producing side reactions such as:

:<sup>11</sup>B + d → <sup>12</sup>C + n + 13.7 MeV
:d + d → <sup>3</sup>He + n + 3.27 MeV

The shielding design reduces the occupational dose of both neutron and gamma radiation to a negligible level. The primary components would be water to moderate the fast neutrons, boron to absorb the moderated neutrons and metal to absorb X-rays. The total thickness is estimated to be about one meter, mostly water.<ref>El Guebaly, Laial, A., Shielding design options and impact on reactor size and cost for the advanced fuel reactor Aploo, Proceedings- Symposium on Fusion Engineering, v.1, 1989, pp.388–391. This design refers to D–He3, which actually produces more neutrons than p–<sup>11</sup>B fuel.</ref>

== Energy capture ==
{{See also|Direct energy conversion}}

Aneutronic fusion produces energy in the form of charged particles instead of [[neutron]]s. This means that energy from aneutronic fusion could be captured using direct conversion instead of the [[steam cycle]]. Direct conversion techniques can either be inductive, based on changes in magnetic fields, electrostatic, based on pitting charged particles against an electric field, or photoelectric, in which light energy is captured. In a pulsed mode.<ref>Miley, G.H., et al., Conceptual design for a B-3He IEC Pilot plant, Proceedings—Symposium on Fusion Engineering, v. 1, 1993, pp. 161–164; L.J. Perkins et al., Novel Fusion energy Conversion Methods, Nuclear Instruments and Methods in Physics Research, A271, 1988, pp. 188–96</ref>

Electrostatic direct conversion uses the motion of charged particles to create [[voltage]]. This voltage drives electricity in a wire. This becomes electrical power, the reverse of most phenomena that use a voltage to put a particle in motion. Direct energy conversion does the opposite, using aparticle motion to produce a voltage. It has been described as a [[linear accelerator]] running backwards.<ref>Moir, Ralph W. "Direct Energy Conversion in Fusion Reactors." Energy Technology Handbook 5 (1977): 150-54. Web. 16 Apr. 2013.</ref> An early supporter of this method was [[Richard F. Post]] at [[Lawrence Livermore National Laboratory|Lawrence Livermore]]. He proposed to capture the [[kinetic energy]] of charged particles as they were exhausted from a fusion reactor and convert this into voltage to drive current.<ref>"Mirror Systems: Fuel Cycles, Loss Reduction and Energy Recovery" R.F. Post, BNES nuclear Fusion Reactor Conference at Culham Labs, September 1969</ref> Post helped develop the theoretical underpinnings of direct conversion, later demonstrated by Barr and Moir. They demonstrated a 48 percent energy capture efficiency on the [[Tandem Mirror Experiment]] in 1981.<ref>"Experimental Results from a beam Direct Converter at 100 kV" W. L. Barr, R. W. Moir and G Hamilton, December 3, 1981, Journal of Fusion Energy Vol 2, No. 2, 1982</ref>

Aneutronic fusion loses much of its energy as light. This energy results from the acceleration and deceleration of charged particles. These speed changes can be caused by Bremsstrahlung radiation or [[cyclotron radiation]] or [[synchrotron radiation]] or electric field interactions. The radiation can be estimated using the [[Larmor formula]] and comes in the X-ray, IR, UV and visible spectra. Some of the energy radiated as X-rays may be converted directly to electricity. Because of the [[photoelectric effect]], X-rays passing through an array of conducting foils transfer some of their energy to electrons, which can then be captured electrostatically. Since X-rays can go through far greater material thickness than electrons, many hundreds or thousands of layers are needed to absorb them.<ref>Quimby, D.C., High Thermal Efficiency X-ray energy conversion scheme for advanced fusion reactors, ASTM Special technical Publication, v.2, 1977, pp. 1161–1165</ref>

== See also ==

* [[History of nuclear fusion]]

== References ==

{{Reflist}}

== External links ==
* [http://www.focusfusion.org/ Focus Fusion Society]
* [https://www.hb11.energy Proton-boron Fusion Prototype ]
* [http://w3.pppl.gov/~fisch/fischpapers/2004/Son_PLA_04.pdf Aneutronic fusion in a degenerate plasma]
* [http://fire.pppl.gov/fusion_lasers_nature_082605.pdf Lasers trigger cleaner fusion] (news@nature.com, 26 August 2005)
* [http://fire.pppl.gov/fusion_pb11_belyaev_082605.pdf Observation of neutronless fusion reactions in picosecond laser plasmas] (Physical Review E 72, 2005)
* [http://fti.neep.wisc.edu/presentations/glk_ans00.pdf New Opportunities for Fusion in the 21st Century – Advanced Fuels], G.L. Kulcinski and J.F.Santarius, 14th Topical Meeting on the Technology of Fusion Energy, Oct 15–19, 2000,
--------------------->

{{Referências}}

{{Portal3|Física}}
{{esboço-física}}
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[[Categoria:Fusão nuclear]]
[[Categoria:Fusão nuclear]]

Revisão das 18h15min de 5 de agosto de 2021

Reações neutrônica e aneutrônica:
1
2
1: Fusão nuclear de deutério-trítio: reação neutrônica gerando energia, produzindo hélio e emitindo um nêutron.
2: Reação de fusão lítio-6 + deutério: reação aneutrônica, na qual a energia liberada é transportada por partículas alfa e não por nêutrons.
Física nuclear

Fusão aneutrônica é qualquer forma de de fusão nuclear em que muito pouca energia liberada é transportada pelos nêutrons. Neste processo, os nêutrons representam menos do que 1% das partículas energizadas resultantes da reação.[1] Enquanto as reações de fusão nuclear de limiar mais baixo liberam até 80% de sua energia na forma de nêutrons, as reações aneutrônicas liberam energia na forma de partículas carregadas, normalmente prótons ou partículas alfa. A fusão aneutrônica bem-sucedida reduziria muito os problemas associados à radiação de nêutrons, como radiação ionizante prejudicial, ativação de nêutrons e requisitos para proteção biológica, manuseio remoto e segurança.

Como é mais simples converter a energia de partículas carregadas em energia elétrica do que converter a energia de partículas não carregadas, uma reação aneutrônica seria atraente para sistemas de energia. Alguns proponentes veem um potencial para reduções dramáticas de custos convertendo energia diretamente em eletricidade, bem como eliminando a radiação dos nêutrons, contra a qual é difícil proteger-se.[2][3] No entanto, as condições necessárias para aproveitar a fusão aneutrônica são muito mais extremas do que aquelas exigidas para a fusão deutério-trítio sendo investigada no ITER.

Reações possíveis

Várias reações nucleares não produzem nêutrons em nenhum de seus ramos. Aquelas com as maiores seções de choque são estas:

Reações aneutrônicas de alta seção de choque.[2]
Isótopos Reação
Deutério - Hélio-3 2D + 3He →   4He + 1p + 18.3 MeV
Deutério - lítio-6 2D + 6Li → 2 4He     + 22.4 MeV
Próton - Lítio-6 1p + 6Li → 4He + 3He + 4.0 MeV
Hélio-3 – Lítio-6 3He + 6Li → 2 4He + 1p + 16.9 MeV
Hélio-3 - Hélio-3 3He + 3He →   4He + 2 1p + 12.86 MeV
Próton – Lítio-7 1p + 7Li → 2 4He     + 17.2 MeV
Próton – Boro-11 1p + 11B → 3 4He     + 8.7 MeV
Próton – Nitrogênio 1p + 15N →   12C + 4He + 5.0 MeV


Referências

  1. ↑ http://www.njleg.state.nj.us/2006/Bills/A3000/2731_I1.HTM
  2. ↑ a b Harms, A. A.; Schoepf, Klaus F.; Kingdon, David Ross (2000). Principles of Fusion Energy: An Introduction to Fusion Energy for Students of Science and Engineering. World Scientific, 2000, (em inglês), págs. 8-11. ISBN 9789812380333 Consultado em 5 de agosto de 2021.
  3. ↑ Larry T. Cox Jr., Franklin B. Mead Jr. and Chan K. Choi Jr., (1990).Thermonuclear Reaction Listing with Cross-Section Data for Four Advanced Reactions, Fusion Technology, Volume 18, no. 2. (em inglês) Consultado em 5 de agosto de 2021.
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