Deuterium fusion

Deuterium fusion, also called deuterium burning, is a nuclear fusion reaction that occurs in stars and some substellar objects, in which a deuterium nucleus and a proton combine to form a helium-3 nucleus. It occurs as the second stage of the proton–proton chain reaction, in which a deuterium nucleus formed from two protons fuses with another proton, but can also proceed from primordial deuterium.

In protostars

Deuterium is the most easily fused nucleus available to accreting protostars,[1] and such fusion in the center of protostars can proceed when temperatures exceed 106 K.[2] The reaction rate is so sensitive to temperature that the temperature does not rise very much above this.[2] The energy generated by fusion drives convection, which carries the heat generated to the surface.[1]

If there were no deuterium fusion, there would be no stars with masses more than about two or three times the mass of the Sun in the pre-main-sequence phase, as the more intense hydrogen fusion would occur and prevent the object from accreting matter.[2] Deuterium fusion allows further accretion of mass by acting as a thermostat that temporarily stops the central temperature from rising above about one million degrees, a temperature not hot enough for hydrogen fusion, but allowing time for the accumulation of more mass.[3] When the energy transport mechanism switches from convective to radiative, energy transport slows, allowing the temperature to rise and hydrogen fusion take over in a stable and sustained way. Hydrogen fusion will begin at 107 K.

The rate of energy generation is proportional to (deuterium concentration)×(density)×(temperature)11.8. If the core is in a stable state, the energy generation will be constant. If one variable in the equation increases, the other two must decrease to keep energy generation constant. As the temperature is raised to the power of 11.8, it would require very large changes in either the deuterium concentration or its density to result in even a small change in temperature.[2][3] The deuterium concentration reflects the fact that the gasses are a mixture of ordinary hydrogen and helium and deuterium.

The mass surrounding the radiative zone is still rich in deuterium, and deuterium fusion proceeds in an increasingly thin shell that gradually moves outwards as the radiative core of the star grows. The generation of nuclear energy in these low-density outer regions causes the protostar to swell, delaying the gravitational contraction of the object and postponing its arrival on the main sequence.[2] The total energy available by deuterium fusion is comparable to that released by gravitational contraction.[3]

Due to the scarcity of deuterium in the Universe, a protostar's supply of it is limited. After a few million years, it will have effectively been completely consumed.[4]

In substellar objects

Hydrogen fusion requires much higher temperatures and pressures than does deuterium fusion, hence, there are objects massive enough to burn deuterium but not massive enough to burn hydrogen. These objects are called brown dwarfs, and have masses between about 13 and 80 times the mass of Jupiter.[5] Brown dwarfs may shine for a hundred million years before their deuterium supply is burned out.[6]

Objects above the deuterium-fusion minimum mass (deuterium burning minimum mass, DBMM) will fuse all their deuterium in a very short time (∼4–50 Myr), whereas objects below that will burn little, and hence, preserve their original deuterium abundance. "The apparent identification of free-floating objects, or rogue planets below the DBMM would suggest that the formation of star-like objects extends below the DBMM."[7]

In planets

It has been shown that deuterium fusion should also be possible in planets. The mass threshold for the onset of deuterium fusion atop the solid cores is also at roughly 13 Jupiter masses.[8][9]

Other reactions

Though fusion with a proton is the dominant method of consuming deuterium, other reactions are possible. These include fusion with another deuterium nucleus to form helium-3, tritium, or (more rarely) helium-4, or with helium to form various isotopes of lithium.[10]

References

  1. ^ a b Adams, Fred C. (1996). Zuckerman, Ben; Malkan, Mathew (eds.). The Origin and Evolution of the Universe. United Kingdom: Jones & Bartlett. p. 47. ISBN 978-0-7637-0030-0.
  2. ^ a b c d e Palla, Francesco; Zinnecker, Hans (2002). Physics of Star Formation in Galaxies. Springer-Verlag. pp. 21–22, 24–25. ISBN 978-3-540-43102-2.
  3. ^ a b c Bally, John; Reipurth, Bo (2006). The birth of stars and planets. Cambridge University Press. p. 61. ISBN 978-0-521-80105-8.
  4. ^ Adams, Fred (2002). Origins of existence: how life emerged in the universe. The Free Press. p. 102. ISBN 978-0-7432-1262-5.
  5. ^ LeBlanc, Francis (2010). An Introduction to Stellar Astrophysics. United Kingdom: John Wiley & Sons. p. 218. ISBN 978-0-470-69956-0.
  6. ^ Lewis, John S. (2004). Physics and chemistry of the solar system. United Kingdom: Elsevier Academic Press. p. 600. ISBN 978-0-12-446744-6.
  7. ^ Chabrier, G.; Baraffe, I.; Allard, F.; Hauschildt, P. (2000). "Deuterium Burning in Substellar Objects". The Astrophysical Journal. 542 (2): L119. arXiv:astro-ph/0009174. Bibcode:2000ApJ...542L.119C. doi:10.1086/312941. Retrieved 2 January 2015.
  8. ^ Mollière, P.; Mordasini, C. (7 November 2012). "Deuterium burning in objects forming via the core accretion scenario". Astronomy & Astrophysics. 547: A105. arXiv:1210.0538. Bibcode:2012A&A...547A.105M. doi:10.1051/0004-6361/201219844.
  9. ^ Bodenheimer, Peter; D'Angelo, Gennaro; Lissauer, Jack J.; Fortney, Jonathan J.; Saumon, Didier (20 June 2013). "Deuterium Burning in Massive Giant Planets and Low-mass Brown Dwarfs Formed by Core-nucleated Accretion". The Astrophysical Journal. 770 (2): 120. arXiv:1305.0980. Bibcode:2013ApJ...770..120B. doi:10.1088/0004-637X/770/2/120.
  10. ^ Rolfs, Claus E.; Rodney, William S. (1988). Cauldrons in the cosmos: nuclear astrophysics. University of Chicago Press. p. 338. ISBN 978-0-226-72456-0.
2M1207b

2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth. It is one of the first candidate exoplanets to be directly observed (by infrared imaging). It was discovered in April 2004 by the Very Large Telescope (VLT) at the Paranal Observatory in Chile by a team from the European Southern Observatory led by Gaël Chauvin. It is believed to be from 3 to 10 times the mass of Jupiter and may orbit 2M1207 at a distance roughly as far from the brown dwarf as Pluto is from the Sun.The object is a very hot gas giant; the estimated surface temperature is roughly 1600 K (1300 °C or 2400 °F), mostly due to gravitational contraction. Its mass is well below the calculated limit for deuterium fusion in brown dwarfs, which is 13 Jupiter masses. The projected distance between 2M1207b and its primary is around 40 AU (similar to the mean distance between Pluto and the Sun). Its infrared spectrum indicates the presence of water molecules in its atmosphere. The object is not a likely candidate to support life, either on its surface or on any satellites.

Brown dwarf

A brown dwarf is a type of substellar object occupying the mass range between the heaviest gas giant planets and the lightest stars, having a mass between approximately 13 to 75–80 times that of Jupiter (MJ), or approximately 2.5×1028 kg to about 1.5×1029 kg. Below this range are the sub-brown dwarfs (sometimes referred to as rogue planets), and above it are the lightest red dwarfs. Brown dwarfs may be fully convective, with no layers or chemical differentiation by depth.Unlike the stars in the main sequence, brown dwarfs are not massive enough to sustain nuclear fusion of ordinary hydrogen (1H) to helium in their cores. They are, however, thought to fuse deuterium (2H) and to fuse lithium (7Li) if their mass is above a debated threshold of 13 MJ and 65 MJ, respectively. It is also debated whether brown dwarfs would be better defined by their formation processes rather than by their supposed nuclear fusion reactions.Stars are categorized by spectral class, with brown dwarfs designated as types M, L, T, and Y. Despite their name, brown dwarfs are of different colors. Many brown dwarfs would likely appear magenta to the human eye, or possibly orange/red. Brown dwarfs are not very luminous at visible wavelengths.

There are planets known to orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b.

At a distance of about 6.5 light years, the nearest known brown dwarf is Luhman 16, a binary system of brown dwarfs discovered in 2013. HR 2562 b is listed as the most-massive known exoplanet (as of December 2017) in NASA's exoplanet archive, despite having a mass (30±15 MJ) more than twice the 13-Jupiter-mass cutoff between planets and brown dwarfs.

Castle Romeo

Castle Romeo was the code name given to one of the tests in the Operation Castle series of American nuclear tests. It was the first test of the TX-17 thermonuclear weapon (initially the "emergency capability" EC-17), the first deployed thermonuclear bomb.

The "Runt" TX-15 device was a weaponized "dry" fusion bomb, using lithium deuteride fuel for the fusion stage of a "staged" fusion bomb, unlike the cryogenic liquid deuterium of the first-generation Ivy Mike fusion device.

Similar to the "Shrimp" TX-21 device tested before in the Castle Bravo test, it differed from that device in using lithium deuteride derived from natural lithium (a mixture of lithium-6 and lithium-7 isotopes, with 7.5% of the former) as the source of the tritium and deuterium fusion fuels, as opposed to the relative high enrichment level of lithium (approximately 40% lithium-6) deuteride used in Bravo.

It was detonated on March 27, 1954, after several delays (which played havoc with the planned experimental measurements program) at Bikini Atoll of the Marshall Islands, on a barge moored in the middle of the crater from the Castle Bravo test. It was the first such barge-based test, a necessity that had come about because the powerful thermonuclear devices completely obliterated the small islands following detonation.

Like the Bravo test, it produced far more than its predicted yield, and for the same reason — an unexpected participation of the common lithium-7 isotope in fusion reactions. Although it had been predicted to produce a yield of 4 megatons with a range of 1.5 to 7 megatons (before the results of the Bravo test caused an upgrade in the estimates, it had originally been estimated to produce 3–5 megatons), it actually produced a yield of 11 megatons, the third-largest test ever conducted by the U.S.

Like the Ivy Mike and Castle Bravo tests, a large percentage of the yield was produced by fast fission of the natural uranium "tamper"; 7 megatons of the yield were from this source.

Fusor (astronomy)

A fusor, according to a proposal to the IAU by Gibor Basri, Professor of Astronomy at the University of California, Berkeley to help clarify the nomenclature of celestial bodies, is "an object that achieves core fusion during its lifetime". This definition included any form of nuclear fusion, so the lowest possible mass of a fusor was set at roughly 13 times that of Jupiter, at which point deuterium fusion becomes possible. This is significantly smaller than the point at which sustained hydrogen fusion becomes possible, around 60 times the mass of Jupiter. Objects are considered "stellar" when they are about 75 times the mass of Jupiter, when gravitational contraction, i.e. contraction of the object due to gravity, is halted by heat generated by the nuclear reaction in their interiors. Fusors would include active stars, dead stars, and brown dwarfs.

The introduction of the term "fusor" would allow for a simple definition:

Fusor – An object capable of core fusion

Planemo – A round nonfusor

Planet – A planemo that orbits a fusorwhere round is understood as "whose surface is very nearly on the gravitational equipotential", orbits means "whose primary orbit is now, or was in the past around", and capable implies fusion is possible sometime during the existence of the object by itself.

Giant planet

A giant planet is any massive planet. They are usually primarily composed of low-boiling-point materials (gases or ices), rather than rock or other solid matter, but massive solid planets can also exist. There are four known giant planets in the Solar System: Jupiter, Saturn, Uranus and Neptune. Many extrasolar giant planets have been identified orbiting other stars.

Giant planets are also sometimes called jovian planets, after Jupiter ("Jove" being another name for the Roman god "Jupiter"). They are also sometimes known as gas giants. However, many astronomers now apply the latter term only to Jupiter and Saturn, classifying Uranus and Neptune, which have different compositions, as ice giants. Both names are potentially misleading: all of the giant planets consist primarily of fluids above their critical points, where distinct gas and liquid phases do not exist. The principal components are hydrogen and helium in the case of Jupiter and Saturn, and water, ammonia and methane in the case of Uranus and Neptune.

The defining differences between a very low-mass brown dwarf and a gas giant (~13 MJ) are debated. One school of thought is based on formation; the other, on the physics of the interior. Part of the debate concerns whether "brown dwarfs" must, by definition, have experienced nuclear fusion at some point in their history.

HD 202206

HD 202206 is a yellow dwarf star approximately 148 light-years away in the constellation Capricornus. The star is orbited by a brown dwarf and a planetary companion in a 5:1 resonant configuration.

HD 202206 b

HD 202206 b is a substellar object orbiting the star HD 202206 approximately 151 light-years away in the constellation of Capricornus. The classification of this object as an extrasolar planet or a brown dwarf is currently unclear. With a mass at least 17.4 times that of Jupiter, it exceeds the limit (approximately 13 Jupiter masses) required for an object to sustain deuterium fusion in its core. The deuterium fusion criterion is used by the IAU's Working Group on Extrasolar Planets to define the boundary between giant planets and brown dwarfs, so in this view HD 202206 b is a brown dwarf. On the other hand, simulations of planet formation by core accretion show that objects of up to 25-30 Jupiter masses can be produced in this way, and therefore the object can potentially be regarded as a planet.

HD 38529

HD 38529 (138 G. Orionis) is a binary star approximately 128 light-years away in the constellation of Orion.

Helion Energy

Helion Energy, Inc. is an American company in Redmond, WA developing a magneto-inertial fusion power technology called The Fusion Engine. Their approach combines the stability of magnetic containment and once-per-second heating pulsed inertial fusion. They are developing a 50 MW scale system.

Impulse drive

In the fictional Star Trek universe, the impulse drive is the method of propulsion that starships and other spacecraft use when they are travelling below the speed of light. Typically powered by deuterium fusion reactors, impulse engines let ships travel interplanetary distances readily. For example, Starfleet Academy cadets use impulse engines when flying from Earth to Saturn and back. Unlike the warp engines, impulse engines work on principles used in today's rocketry, throwing mass out the back as fast as possible to drive the ship forward.

Inertial electrostatic confinement

Inertial electrostatic confinement is a branch of fusion research that uses an electric field to elevate a plasma to fusion conditions. Electric fields can do work on charged particles (either ions or electrons), heating/confining them to fusion conditions. This is typically done in a sphere, with material moving radially inward, but can also be done in a cylindrical or beam geometry. The electric field can be generated using a wire grid or a non-neutral plasma cloud.

Isotopes of sodium

There are 21 recognized isotopes of sodium (11Na), ranging from 18Na to 39Na and two isomers (22mNa and 24mNa). 23Na is the only stable (and the only primordial) isotope. As such, it is considered a monoisotopic element and it has a standard atomic weight of 22.98976928(2). Sodium has two radioactive cosmogenic isotopes (22Na, half-life = 2.605 years; and 24Na, half-life ≈ 15 hours). With the exception of those two, all other isotopes have half-lives under a minute, most under a second. The shortest-lived is 18Na, with a half-life of 1.3(4)×10−21 seconds.

Acute neutron radiation exposure (e.g., from a nuclear criticality accident) converts some of the stable 23Na in human blood plasma to 24Na. By measuring the concentration of this isotope, the neutron radiation dosage to the victim can be computed.

22Na is a positron-emitting isotope with a remarkably long half-life. It is used to create test-objects and point-sources for positron emission tomography.

Kepler-25b

Kepler-25b is an extrasolar planet orbiting the star Kepler-25, located in the constellation Cygnus. It was discovered by the Kepler Space Telescope in 2012. Kepler-25b is one of the most massive planets ever found. if it had the equivalent of 1 extra Saturn mass, it would be considered a brown dwarf, as it has ≈12,7 Jupiter Masses. ≥13 Jupiter Masses is required for deuterium fusion.

Levitated dipole

A levitated dipole is a type of nuclear fusion reactor design using a superconducting torus which is magnetically levitated inside the reactor chamber. The name refers to the magnetic dipole that forms within the reaction chamber, similar to Earth's or Jupiter's magnetospheres. It is believed that such an apparatus could contain plasma more efficiently than other fusion reactor designs.The Levitated Dipole Experiment (LDX) was funded by the US Department of Energy's Office of Fusion Energy. The machine was run in a collaboration between MIT and Columbia University. Funding for the LDX was ended in November 2011 to concentrate resources on tokamak designs.

Mark 16 nuclear bomb

The Mark 16 nuclear bomb was a large thermonuclear bomb (hydrogen bomb), based on the design of the Ivy Mike, the first thermonuclear device ever test fired. The Mark 16 is more properly designated TX-16/EC-16 as it only existed in Experimental/Emergency Capability (EC) versions.

The TX-16 was notable because it was the only deployed thermonuclear bomb which used a cryogenic liquid deuterium fusion fuel, the same fuel used in the Ivy Mike test device. The TX-16 was in fact a weaponized version of the Ivy Mike design. This required both a considerable reduction in weight of the explosive package and the replacement of the elaborate cryogenic system with vacuum flasks for replenishing boiled-off deuterium. The carrier aircraft was to be the B-36 as modified under Operation Barroom.

Only one B-36 was so modified. The TX-16 shared common forward and aft casing sections with the TX-14 and TX-17/24 and in the emergency capability (EC-16) version was almost indistinguishable from the EC-14. A small number of EC-16s were produced to provide a stop-gap thermonuclear weapon capability in response to the Russian nuclear weapons program. The TX-16 was scheduled to be tested as the Castle Yankee "Jughead" device until the overwhelming success of the Castle Bravo "Shrimp" test device rendered it obsolete.

S-process

The slow neutron-capture process , or s-process is a series of reactions in nuclear astrophysics that occur in stars, particularly AGB stars. The s-process is responsible for the creation (nucleosynthesis) of approximately half the atomic nuclei heavier than iron.

In the s-process, a seed nucleus undergoes neutron capture to form an isotope with one higher atomic mass. If the new isotope is stable, a series of increases in mass can occur, but if it is unstable, then beta decay will occur, producing an element of the next highest atomic number. The process is slow (hence the name) in the sense that there is sufficient time for this radioactive decay to occur before another neutron is captured. A series of these reactions produces stable isotopes by moving along the valley of beta-decay stable isobars in the table of nuclides.

A range of elements and isotopes can be produced by the s-process, because of the intervention of alpha decay steps along the reaction chain. The relative abundances of elements and isotopes produced depends on the source of the neutrons and how their flux changes over time. Each branch of the s-process reaction chain eventually terminates at a cycle involving lead, bismuth, and polonium.

The s-process contrasts with the r-process, in which successive neutron captures are rapid: they happen more quickly than the beta decay can occur. The r-process dominates in environments with higher fluxes of free neutrons; it produces heavier elements and more neutron-rich isotopes than the s-process. Together the two processes account for most of the relative abundance of chemical elements heavier than iron.

Taylor Wilson

Taylor Ramon Wilson (born May 7, 1994) is an American nuclear physics enthusiast and science advocate. In 2008, at the age of 14, he produced nuclear fusion using a fusor and at the time was the youngest person ever to do so.

Timeline of hydrogen technologies

This is a timeline of the history of hydrogen technology.

Radioactive
decay
Stellar
nucleosynthesis
Other
processes

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