Nuclear fusion is a reaction whereby two or more atomic nuclei fuse to become different atomic nuclei, neutrons or protons. The net change in mass results in the release or absorption of energy. Fusion is the process that maintains main sequence stars, releasing tremendous amounts of energy. Fusion of lighter nuclei is an exothermic process, while fusion of heavier nuclei results in an endothermic reaction. Hydrogen and helium, are more suitable for fusion, whilst heavier elements, such as uranium and plutonium undergo nuclear fission.
What is nuclear fusion?
The Sun is a main-sequence star, creating its own energy via nuclear fusion of hydrogen nuclei into helium. The Sun fuses 500 million metric tons of hydrogen per second.
Discovery of nuclear fusion
Eddington proposed that hydrogen-helium fusion could be the source of stellar energy. Quantum tunneling was also suggested in 1929. Atkinson and Houtermans showed that tremendous energy could be released by fusing small nuclei. Fusion of hydrogen isotopes was accomplished by Mark Oliphant in 1932. The military prioritised fusion research in the early 1940s, as part of the infamous Manhattan Project. Nuclear fusion on a large scale was first carried out on 1 November 1952, as part of the Ivy Mike ‘hydrogen bomb’ test. Global research into controlled fusion has been ongoing since the 1940s. The technology is progressing but remains at an early stage.
ITER objectives in the future
Produce 500 MW of fusion power for pulses of 400 s
Demonstrate the operation for a fusion power plant
Create plasma in which the reaction is sustained through internal heating
Test tritium breeding
Demonstrate the safety characteristics of a fusion device
Nuclear fusion reaction
The fusion of deuterium with tritium produces helium-4, releasing 17.59 MeV as kinetic energy, while mass disappears, ,kinetic E = ∆mc2, Δm is the decrease in the total rest mass of particles.
Fusion and Coulomb force
Two opposing forces determine the energy released, the nuclear force, which combines together protons and neutrons and the Coulomb force, where repel each other. Light nuclei allow the nuclear force to overcome repulsion. 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 the extra energy from the net attraction of particles.
Nucleosynthesis and fusion
Fusion in the stars is called nucleosynthesis. The Sun liberates approximately 610 million metric tons of helium per second. The fusion of lighter elements in stars releases energy and mass. In the fusion of two hydrogen nuclei, 0.645% of the mass is lost as kinetic energy of an alpha particle or other forms of energy, such as electromagnetic radiation.
When accelerated to high speeds, nuclei can overcome the electrostatic repulsion. The fusion of lighter nuclei, which creates a heavier nucleus and often a free neutron or proton, releases more energy than it takes to bind the nuclei. This is an exothermic process.
Energy released in most nuclear reactions is larger than in chemical reactions. The ionisation energy gained by adding an electron to a hydrogen nucleus is 13.6 eV, which is less than one-millionth of the 17.6 MeV released in the deuterium–tritium fusion reaction. Fusion reactions produce far greater energy per unit of mass even though individual fission reactions are generally much more energetic than individual fusion ones.
Nuclear fusion research
Currently, controlled fusion reactions have been unable to produce net zero energy. The two most advanced approaches for it are magnetic confinement and inertial confinement designs. A prototype toroidal reactor that will deliver ten times more fusion energy than the amount needed to heat plasma are in development ITER. The ITER facility is expected to finish its construction phase in 2025. General Fusion (Canada), is developing a magnetised target fusion nuclear energy system. The US National Ignition Facility, is approaching the challenge via laser-driven inertial confinement fusion.
Nuclear fusion – stars
Stellar nucleosynthesis powers stars. The energy released from nuclear fusion reactions accounts for the longevity of stellar heat and light. The fusion of nuclei in a star provides that energy and synthesises new nuclei. Different reaction chains are involved, depending on the mass of the star.
Eddington’s theory on fusion
Approximately 1920, Eddington’s published his paper The Internal Constitution of the Stars. Eddington stated that the concept was fusion of hydrogen into helium, liberating enormous energy according to Einstein’s equation E = mc2.
Eddington’s papers suggested that the theory of stellar energy, the contraction hypothesis, should cause stars’ rotation to visibly speed up due to conservation of angular momentum. Additionally, energy was liberated from the conversion of matter to energy. Aston proposed that the mass of a helium atom was about 0.8% less than the mass of the four hydrogen atoms. He concluded that if fusion could occur, it would release considerable energy. In conclusion, if a star contained just 5% of fusible hydrogen, this explained how stars retained their energy.
Nuclear fusion conditions
This proton-proton chain reaction occurs at 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. As a star uses up a fraction of its hydrogen, it begins to synthesise heavier elements. The heaviest elements are synthesised by fusion that occurs when a more massive star undergoes a violent supernova at the end of its life, a process known as supernova nucleosynthesis.
Nuclear fusion reactor – what is a tokamak?
A tokamak is designed to harness the energy of fusion. The donut shape chamber, the name derived from a Russian acronym meaning toroidal chamber with magnetic coils. As per any other type of power station, a fusion power plant will use the heat generated to produce steam and then electricity via turbines and generators.
Through an environment of extreme heat and pressure, gaseous hydrogen fuel becomes a plasma. The charged particles can be shaped and controlled by the magnetic coils. The coils prevent the hot plasma from contacting the vessel walls.
How does a nuclear fusion tokamak work?
Air and impurities are first evacuated from the vacuum chamber. The gaseous fuel is then introduced and a powerful electrical current is passed through the vessel, and the gas becomes ionised resulting in the plasma. As the plasma particles become energised and collide they also begin to heat up. The plasma is modulated to fusion temperatures 150 and 300 million °C. Particles overcome their electromagnetic repulsion and fuse, releasing tremendous energy.
Types of nuclear fusion
Thermonuclear weapons lead to an uncontrolled release of fusion energy. Controlled thermonuclear fusion concepts use magnetic fields to confine the plasma, as per the tokamak design.
Inertial confinement fusion
Inertial confinement fusion (ICF) is a method aimed at releasing fusion energy by heating and compressing a fuel target, typically a pellet containing deuterium and tritium.
Inertial electrostatic confinement
Inertial electrostatic confinement is a set of devices that use an electric field to heat ions to fusion conditions. The most well known 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: the Polywell, MIX POPS and Marble concepts.
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- Shultis, J.K. & Faw, R.E. (2002). Fundamentals of nuclear science and engineering. CRC Press. p. 151. ISBN 978-0-8247-0834-4.
- Physics Flexbook Archived 28 December 2011 at the Wayback Machine. Ck12.org. Retrieved 19 December 2012.
- Bethe, Hans A. (April 1950). “The Hydrogen Bomb”. Bulletin of the Atomic Scientists. 6 (4): 99–104, 125–. Bibcode:1950BuAtS…6d..99B. doi:10.1080/00963402.1950.11461231.
- “Progress in Fusion”. ITER. Retrieved 15 February 2010.
- “ITER – the way to new energy”. ITER. 2014. Archived from the original on 22 September 2012.
- Boyle, Alan (16 December 2019). “General Fusion gets a $65M boost for fusion power plant from investors – including Jeff Bezos”. GeekWire.
- Moses, E. I. (2009). “The National Ignition Facility: Ushering in a new age for high energy density science”. Physics of Plasmas. 16 (4): 041006. Bibcode:2009PhPl…16d1006M. doi:10.1063/1.3116505.
- Kramer, David (March 2011). “DOE looks again at inertial fusion as potential clean-energy source”. Physics Today. 64 (3): 26–28. Bibcode:2011PhT….64c..26K. doi:10.1063/1.3563814.
- Eddington, A. S. (October 1920). “The Internal Constitution of the Stars”. The Scientific Monthly. 11 (4): 297–303. Bibcode:1920Sci….52..233E. doi:10.1126/science.52.1341.233. JSTOR 6491. PMID 17747682.
- Eddington, A. S. (1916). “On the radiative equilibrium of the stars”. Monthly Notices of the Royal Astronomical Society. 77: 16–35. Bibcode:1916MNRAS..77…16E. doi:10.1093/mnras/77.1.16.
- The Most Tightly Bound Nuclei. Hyperphysics.phy-astr.gsu.edu. Retrieved 17 August 2011.
- What Is The Lawson Criteria, Or How to Make Fusion Power Viable
- “Fusor Forums • Index page”. Fusor.net. Retrieved 24 August 2014.
- “Build a Nuclear Fusion Reactor? No Problem”. Clhsonline.net. 23 March 2012. Archived from the original on 30 October 2014. Retrieved 24 August 2014.
- Danzico, Matthew (23 June 2010). “Extreme DIY: Building a homemade nuclear reactor in NYC”. Retrieved 30 October 2014.
- Schechner, Sam (18 August 2008). “Nuclear Ambitions: Amateur Scientists Get a Reaction From Fusion – WSJ”. The Wall Street Journal. Retrieved 24 August2014.
- Park J, Nebel RA, Stange S, Murali SK (2005). “Experimental Observation of a Periodically Oscillating Plasma Sphere in a Gridded Inertial Electrostatic Confinement Device”. Phys Rev Lett. 95 (1): 015003. Bibcode:2005PhRvL..95a5003P. doi:10.1103/PhysRevLett.95.015003. PMID 16090625.
- “The Multiple Ambipolar Recirculating Beam Line Experiment” Poster presentation, 2011 US-Japan IEC conference, Dr. Alex Klein
- J. Slough, G. Votroubek, and C. Pihl, “Creation of a high-temperature plasma through merging and compression of supersonic field reversed configuration plasmoids” Nucl. Fusion 51,053008 (2011).
- A. Asle Zaeem et al “Aneutronic Fusion in Collision of Oppositely Directed Plasmoids” Plasma Physics Reports, Vol. 44, No. 3, pp. 378–386 (2018).
- Jones, S.E. (1986). “Muon-Catalysed Fusion Revisited”. Nature. 321 (6066): 127–133. Bibcode:1986Natur.321..127J. doi:10.1038/321127a0. S2CID 39819102.
- Supplementary methods for “Observation of nuclear fusion driven by a pyroelectric crystal”. Main article Naranjo, B.; Gimzewski, J.K.; Putterman, S. (2005). “Observation of nuclear fusion driven by a pyroelectric crystal”. Nature. 434 (7037): 1115–1117. Bibcode:2005Natur.434.1115N. doi:10.1038/nature03575. PMID 15858570. S2CID 4407334.
- UCLA Crystal Fusion. Rodan.physics.ucla.edu. Retrieved 17 August 2011. Archived 8 June 2015 at the Wayback Machine
- Schewe, Phil & Stein, Ben (2005). “Pyrofusion: A Room-Temperature, Palm-Sized Nuclear Fusion Device”. Physics News Update. 729 (1). Archived from the original on 12 November 2013.
- Coming in out of the cold: nuclear fusion, for real. The Christian Science Monitor. (6 June 2005). Retrieved 17 August 2011.
- Nuclear fusion on the desktop … really!. MSNBC (27 April 2005). Retrieved 17 August 2011.
- Gerstner, E. (2009). “Nuclear energy: The hybrid returns”. Nature. 460 (7251): 25–8. doi:10.1038/460025a. PMID 19571861.
- Maugh II, Thomas. “Physicist is found guilty of misconduct”. Los Angeles Times. Retrieved 17 April 2019.
- FusEdWeb | Fusion Education. Fusedweb.pppl.gov (9 November 1998). Retrieved 17 August 2011. Archived 24 October 2007 at the Wayback Machine
- M. Kikuchi, K. Lackner & M. Q. Tran (2012). Fusion Physics. International Atomic Energy Agency. p. 22. ISBN 9789201304100.
- K. Miyamoto (2005). Plasma Physics and Controlled Nuclear Fusion. Springer-Verlag. ISBN 3-540-24217-1.
- Subsection 4.7.4c Archived 16 August 2018 at the Wayback Machine. Kayelaby.npl.co.uk. Retrieved 19 December 2012.
- A momentum and energy balance shows that if the tritium has an energy of ET(and using relative masses of 1, 3, and 4 for the neutron, tritium, and helium) then the energy of the helium can be anything from [(12ET)1/2−(5×17.6MeV+2×ET)1/2]2/25 to [(12ET)1/2+(5×17.6MeV+2×ET)1/2]2/25. For ET=1.01 MeV this gives a range from 1.44 MeV to 6.73 MeV.
- Rider, Todd Harrison (1995). “Fundamental Limitations on Plasma Fusion Systems not in Thermodynamic Equilibrium”. Dissertation Abstracts International. 56-07 (Section B): 3820. Bibcode:1995PhDT……..45R.
- Rostoker, Norman; Binderbauer, Michl and Qerushi, Artan. Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium. fusion.ps.uci.edu
- Huba, J. (2003). “NRL PLASMA FORMULARY” (PDF). MIT Catalog. Retrieved 11 November 2018.
- Bosch, H. S (1993). “Improved formulas for fusion cross-sections and thermal reactivities”. Nuclear Fusion. 32 (4): 611–631. doi:10.1088/0029-5515/32/4/I07. S2CID 55303621.