Deuterium–tritium fusion (DTF) is a type of nuclear fusion in which one deuterium (2H) nucleus (deuteron) fuses with one tritium (3H) nucleus (triton), giving one helium-4 nucleus, one free neutron, and 17.6 MeV of total energy coming from both the neutron and helium. It is the best known fusion reaction for fusion power and thermonuclear weapons.
Tritium, one of the reactants for DTF, is radioactive. In fusion reactors, a 'breeding blanket' made of lithium is placed on the walls of the reactor, as lithium, when exposed to energetic neutrons, will produce tritium.
Concept
editIn DTF, one deuteron fuses with one tritium, yielding one helium nucleus, a free neutron, and 17.6 MeV, which is derived from about 0.02 AMU.[1] The amount of energy obtained is described by the mass–energy equivalence: E = mc2. 80% of the energy (14.1 MeV) becomes kinetic energy of the neutron traveling at 1/6 the speed of light.
The mass difference between 2H+3H and neutron+4He is described by the semi-empirical mass formula that describes the relation between mass defects and binding energy in a nucleus.
Discovery
editEvidence of DTF was first detected at the University of Michigan in 1938 by Arthur J. Ruhlig.[2][3] His experiment detected the signature of neutrons with energy greater than 15 MeV in secondary reactions of 3H created in 2H(d,p)3H reactions of a 0.5 MeV incident deuteron beam on a heavy phosphoric acid target, 2H3PO4. This discovery was largely unrecognized until recently.[4]
Reactant sourcing
editAbout 1 in every 6700 hydrogen atoms in seawater is deuterium, making it easy to acquire.[1][5]
Tritium, however, is a radioisotope, and can't be sourced naturally. This can be circumvented by exposing lithium to energetic neutrons, which produces tritons.[1][5] Also, DTF itself emits a free neutron, which can be used to bombard lithium.[6] A 'breeding blanket', made of lithium, is often placed along the walls of fusion reactors so that free neutrons created by DTF react with it to produce more 3H.[7][8] This process is called tritium breeding.
Fusion reactors
editDTF is planned to be used in ITER,[7] and many other proposed fusion reactors. It has many advantages over other types of fusion, as it has a relatively low minimum temperature, 108 kelvin.[9]
Spin polarization
editSpin-polarized D-T fuel can increase tritium burn efficiency (TBE) by an order of magnitude or more without compromising output. TBE increases nonlinearly with decreasing tritium fraction, while power density increases roughly linearly with D-T cross section. In a 481 MW ARC-like tokamak with unpolarized 53:47 D-T fuel, the minimum tritium inventory was 0.69 kg. Spin-polarizing the fuel with a 63:37 D-T mix reduces the required tritium to 0.03 kg. With advancements in helium divertor pumping efficiency, TBE values of approximately 10%–40% could be achieved using low-tritium-fraction spin-polarized fuel with minimal power loss. This lowers tritium startup inventory requirements.[10]
See also
editReferences
edit- ^ a b c "Nuclear Fusion". Georgia State University. Retrieved January 29, 2021.
- ^ Ruhlig, Arthur (15 August 1938). "Search for Gamma-Rays from the Deuteron-Deuteron Reaction". Phys. Rev. 54 (4): 308. doi:10.1103/PhysRev.54.308. Retrieved February 6, 2024.
- ^ Chadwick, M. B. (2023). "The earliest DT nuclear fusion discoveries". arXiv:2302.04206.
- ^ Paris, Mark W.; Chadwick, Mark B. (2023-10-01). "A lost detail in D–T fusion history". Physics Today. 76 (10): 10–11. doi:10.1063/PT.3.5317. ISSN 0031-9228.
- ^ a b Lanctot, Matthew. "DOE Explains...deuterium–tritium Fusion Reactor Fuel". Department of Energy. Retrieved April 12, 2021.
- ^ Cowley, Steve. "Introduction to Fusion Part I." (PDF). SULI. Retrieved January 30, 2021.
- ^ a b "Fueling the Fusion Reaction". ITER. Retrieved February 12, 2021.
- ^ "Tritium: a challenging fuel for fusion". EUROfusion. November 8, 2017. Retrieved February 16, 2021.
- ^ Schneider, Ursula (August 1, 2001). "Fusion: Energy of the Future". International Atomic Energy Agency. Retrieved February 13, 2021.
- ^ Parisi, J.F.; Diallo, A.; Schwartz, J.A. (2024-12-01). "Simultaneous enhancement of tritium burn efficiency and fusion power with low-tritium spin-polarized fuel". Nuclear Fusion. 64 (12): 126019. doi:10.1088/1741-4326/ad7da3. ISSN 0029-5515.