Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Nuclear weapon design
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
==Two-stage thermonuclear== {{Main|Thermonuclear weapon}} [[File:IvyMikeGIFColorCorrected.gif|thumb|right|[[Ivy Mike]], the first two-stage thermonuclear detonation, 10.4 megatons, November 1, 1952.]] Pure fission or fusion-boosted fission weapons can be made to yield hundreds of kilotons, at great expense in fissile material and tritium, but by far the most efficient way to increase nuclear weapon yield beyond ten or so kilotons is to add a second independent stage, called a secondary.{{Citation needed|date=June 2021}} In the 1940s, bomb designers at [[Los Alamos National Laboratory|Los Alamos]] thought the secondary would be a canister of deuterium in liquefied or hydride form. The fusion reaction would be D-D, harder to achieve than D-T, but more affordable. A fission bomb at one end would shock-compress and heat the near end, and fusion would propagate through the canister to the far end. Mathematical simulations showed it would not work, even with large amounts of expensive tritium added.{{Citation needed|date=June 2021}} The entire fusion fuel canister would need to be enveloped by fission energy, to both compress and heat it, as with the booster charge in a boosted primary. The design breakthrough came in January 1951, when [[Edward Teller]] and [[Stanislaw Ulam]] invented radiation implosion β for nearly three decades known publicly only as the [[Teller-Ulam]] H-bomb secret.<ref>[https://www.aip.org/history-programs/niels-bohr-library/oral-histories/35680 So I pieced together from Edward's testament and from his memoir that Stan had come to him in February of 1951] {{Webarchive|url=https://web.archive.org/web/20180213135308/https://www.aip.org/history-programs/niels-bohr-library/oral-histories/35680 |date=2018-02-13}} American Institute of Physics interview with Richard Garwin by Ken Ford, dated December 2012</ref><ref>[https://www.aip.org/history-programs/niels-bohr-library/oral-histories/28636-1 he was going to use first hydrodynamics and just the shockwaves and then neutron heating, which would have been a disaster. It would have blown it up before it got going. It was Teller who came up with the radiation.] {{Webarchive|url=https://web.archive.org/web/20210223052546/https://www.aip.org/history-programs/niels-bohr-library/oral-histories/28636-1 |date=2021-02-23}}, American Institute of Physics interview with Marshall Rosenbluth by Kai-Henrik Barth, dated August 2003</ref> The concept of radiation implosion was first tested on May 9, 1951, in the George shot of [[Operation Greenhouse]], Eniwetok, yield 225 kilotons. The first full test was on November 1, 1952, the [[Ivy Mike|Mike]] shot of [[Operation Ivy]], Eniwetok, yield 10.4 megatons.{{Citation needed|date=June 2021}} In radiation implosion, the burst of X-ray energy coming from an exploding primary is captured and contained within an opaque-walled radiation channel which surrounds the nuclear energy components of the secondary. The radiation quickly turns the plastic foam that had been filling the channel into a plasma which is mostly transparent to X-rays, and the radiation is absorbed in the outermost layers of the pusher/tamper surrounding the secondary, which ablates and applies a massive force<ref>[https://nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html#Nfaq4.4.3.3 4.4 Elements of Thermonuclear Weapon Design] {{webarchive |url=https://web.archive.org/web/20160311152031/https://nuclearweaponarchive.org/Nwfaq/Nfaq4-4.html#Nfaq4.4.3.3 |date=March 11, 2016}}. Nuclearweaponarchive.org. Retrieved on 2011-05-01.</ref> (much like an inside out rocket engine) causing the fusion fuel capsule to implode much like the pit of the primary. As the secondary implodes a fissile "spark plug" at its center ignites and provides neutrons and heat which enable the lithium deuteride fusion fuel to produce tritium and ignite as well. The fission and fusion chain reactions exchange neutrons with each other and boost the efficiency of both reactions. The greater implosive force, enhanced efficiency of the fissile "spark plug" due to boosting via fusion neutrons, and the fusion explosion itself provide significantly greater explosive yield from the secondary despite often not being much larger than the primary.{{Citation needed|date=June 2021}} [[File:TellerUlamAblation.png|center|thumb|700px|Ablation mechanism firing sequence. {{Ordered list |Warhead before firing. The nested spheres at the top are the fission primary; the cylinders below are the fusion secondary device.|Fission primary's explosives have detonated and collapsed the primary's [[plutonium pit|fissile pit]]. |The primary's fission reaction has run to completion, and the primary is now at several million degrees and radiating gamma and hard X-rays, heating up the inside of the [[hohlraum]], the shield, and the secondary's tamper. |The primary's reaction is over and it has expanded. The surface of the pusher for the secondary is now so hot that it is also ablating or expanding away, pushing the rest of the secondary (tamper, fusion fuel, and fissile spark plug) inward. The spark plug starts to fission. Not depicted: the radiation case is also ablating and expanding outward (omitted for clarity of diagram). |The secondary's fuel has started the fusion reaction and shortly will burn up. A fireball starts to form. }}]] For example, for the Redwing Mohawk test on July 3, 1956, a secondary called the Flute was attached to the Swan primary. The Flute was {{convert|15|in|cm|order=flip}} in diameter and {{convert|23.4|in|cm|order=flip}} long, about the size of the Swan. But it weighed ten times as much and yielded 24 times as much energy (355 kilotons vs 15 kilotons).{{Citation needed|date=June 2021}} Equally important, the active ingredients in the Flute probably cost no more than those in the Swan. Most of the fission came from cheap U-238, and the tritium was manufactured in place during the explosion. Only the spark plug at the axis of the secondary needed to be fissile.{{Citation needed|date=June 2021}} A spherical secondary can achieve higher implosion densities than a cylindrical secondary, because spherical implosion pushes in from all directions toward the same spot. However, in warheads yielding more than one megaton, the diameter of a spherical secondary would be too large for most applications. A cylindrical secondary is necessary in such cases. The small, cone-shaped re-entry vehicles in multiple-warhead ballistic missiles after 1970 tended to have warheads with spherical secondaries, and yields of a few hundred kilotons.{{Citation needed|date=June 2021}} In engineering terms, radiation implosion allows for the exploitation of several known features of nuclear bomb materials which heretofore had eluded practical application. For example: * The optimal way to store deuterium in a reasonably dense state is to chemically bond it with lithium, as lithium deuteride. But the lithium-6 isotope is also the raw material for tritium production, and an exploding bomb is a nuclear reactor. Radiation implosion will hold everything together long enough to permit the complete conversion of lithium-6 into tritium, while the bomb explodes. So the bonding agent for deuterium permits use of the D-T fusion reaction without any pre-manufactured tritium being stored in the secondary. The tritium production constraint disappears.{{Citation needed|date=June 2021}} * For the secondary to be imploded by the hot, radiation-induced plasma surrounding it, it must remain cool for the first microsecond, i.e., it must be encased in a massive radiation (heat) shield. The shield's massiveness allows it to double as a tamper, adding momentum and duration to the implosion. No material is better suited for both of these jobs than ordinary, cheap uranium-238, which also happens to undergo fission when struck by the neutrons produced by D-T fusion. This casing, called the pusher, thus has three jobs: to keep the secondary cool; to hold it, inertially, in a highly compressed state; and, finally, to serve as the chief energy source for the entire bomb. The consumable pusher makes the bomb more a uranium fission bomb than a hydrogen fusion bomb. Insiders never used the term "hydrogen bomb".<ref>Until a reliable design was worked out in the early 1950s, the hydrogen bomb (public name) was called the superbomb by insiders. After that, insiders used a more descriptive name: two-stage thermonuclear. Two examples. From Herb York, ''The Advisors'', 1976, "This book is about ... the development of the H-bomb, or the superbomb as it was then called." p. ix, and "The rapid and successful development of the superbomb (or super as it came to be called) ..." p. 5. From National Public Radio Talk of the Nation, November 8, 2005, Siegfried Hecker of Los Alamos, "the hydrogen bomb β that is, a two-stage thermonuclear device, as we referred to it β is indeed the principal part of the US arsenal, as it is of the Russian arsenal."</ref> * Finally, the heat for fusion ignition comes not from the primary but from a second fission bomb called the spark plug, embedded in the heart of the secondary. The implosion of the secondary implodes this spark plug, detonating it and igniting fusion in the material around it, but the spark plug then continues to fission in the neutron-rich environment until it is fully consumed, adding significantly to the yield.<ref name="CLR"/> In the ensuing fifty years, no one has come up with a more efficient way to build a thermonuclear bomb. It is the design of choice for the United States, Russia, the United Kingdom, China, and France, the five thermonuclear powers. On 3 September 2017 [[2017 North Korean nuclear test|North Korea carried out]] what it reported as its first "two-stage thermo-nuclear weapon" test.<ref name=cnbc-20170903>{{cite news |title=North Korea hydrogen bomb: Read the full announcement from Pyongyang |last=Kemp |first=Ted |publisher=CNBC News |date=3 September 2017 |url=https://www.cnbc.com/2017/09/03/north-korea-hydrogen-bomb-read-the-full-announcement-from-pyongyang.html |access-date=5 September 2017 |url-status=live |archive-url=https://web.archive.org/web/20170904051152/https://www.cnbc.com/2017/09/03/north-korea-hydrogen-bomb-read-the-full-announcement-from-pyongyang.html |archive-date=4 September 2017}}</ref> According to [[Ted Taylor (physicist)|Dr. Theodore Taylor]], after reviewing leaked [[Mordechai Vanunu#Negev Nuclear Research Center|photographs]] of disassembled weapons components taken before 1986, Israel possessed boosted weapons and would require supercomputers of that era to advance further toward full two-stage weapons in the megaton range without nuclear test detonations.<ref>{{cite web |title=Israel's Nuclear Weapon Capability: An Overview |website=wisconsinproject.org |url=https://www.wisconsinproject.org/israels-nuclear-weapon-capability-an-overview/ |access-date=2016-10-03 |url-status=dead |archive-url=https://web.archive.org/web/20150429192508/http://www.wisconsinproject.org/countries/israel/nuke.html |archive-date=2015-04-29}}</ref> The other nuclear-armed nations, India and Pakistan, probably have single-stage weapons, possibly boosted.<ref name="CLR"/> ===Interstage=== In a two-stage thermonuclear weapon the energy from the primary impacts the secondary. An essential{{Citation needed|date=June 2021|reason=Details released about Ivy Mike suggest an interstage is not needed for larger weapons}} energy transfer modulator called the interstage, between the primary and the secondary, protects the secondary's fusion fuel from heating too quickly, which could cause it to explode in a conventional (and small) heat explosion before the fusion and fission reactions get a chance to start.{{Citation needed|date=June 2021|reason=While some might modulate, the important part is filling the radiation channels with low-Z plasma that is not opaque to radiation like high-Z plasma}} There is very little information in the open literature about the mechanism of the interstage.{{Citation needed|date=June 2021|reason=details of plasma opacity can be found in ICF literature}} Its first mention in a U.S. government document formally released to the public appears to be a caption in a graphic promoting the Reliable Replacement Warhead Program in 2007. If built, this new design would replace "toxic, brittle material" and "expensive 'special' material" in the interstage.<ref>[[commons:File:Reliable Replacement Warhead Features.jpg|"Improved Security, Safety & Manufacturability of the Reliable Replacement Warhead"]], NNSA March 2007.</ref> This statement suggests the interstage may contain beryllium to moderate the flux of neutrons from the primary, and perhaps something to absorb and re-radiate the x-rays in a particular manner.<ref>[https://fas.org/sgp/eprint/morland_image026.gif A 1976 drawing] {{webarchive |url=https://web.archive.org/web/20160403132417/https://fas.org/sgp/eprint/morland_image026.gif |date=April 3, 2016}} which depicts an interstage that absorbs and re-radiates x-rays. From Howard Morland, [https://fas.org/sgp/eprint/cardozo.html "The Article"], {{webarchive |url=https://web.archive.org/web/20160322014302/https://fas.org/sgp/eprint/cardozo.html |date=March 22, 2016}} ''Cardozo Law Review'', March 2005, p. 1374.</ref> There is also some speculation that this interstage material, which may be code-named [[Fogbank]], might be an [[aerogel]], possibly doped with beryllium and/or other substances.<ref>{{cite news |title=Technical hitch delays renewal of nuclear warheads for Trident |author=Ian Sample |newspaper=[[The Guardian]] |date=6 March 2008 |url=https://www.theguardian.com/uk/2008/mar/06/military.greenpolitics?gusrc=rss&feed=politics |access-date=15 December 2016 |url-status=live |archive-url=https://web.archive.org/web/20160305035909/http://www.theguardian.com/uk/2008/mar/06/military.greenpolitics?gusrc=rss&feed=politics |archive-date=5 March 2016}}</ref><ref>[https://www.armscontrolwonk.com/archive/201814/fogbank/ "ArmsControlWonk: FOGBANK"] {{webarchive |url=https://web.archive.org/web/20100114172137/http://www.armscontrolwonk.com/1814/fogbank |date=January 14, 2010}}, March 7, 2008. (Accessed 2010-04-06)</ref> The interstage and the secondary are encased together inside a stainless steel membrane to form the canned subassembly (CSA), an arrangement which has never been depicted in any open-source drawing.<ref>[https://fas.org/sgp/eprint/w-88sand.htm "SAND8.8 β 1151 Nuclear Weapon Data β Sigma I"], {{webarchive |url=https://web.archive.org/web/20160423004514/https://fas.org/sgp/eprint/w-88sand.htm |date=April 23, 2016}} Sandia Laboratories, September 1988.</ref> The most detailed illustration of an interstage shows a British thermonuclear weapon with a cluster of items between its primary and a cylindrical secondary. They are labeled "end-cap and neutron focus lens", "reflector/neutron gun carriage", and "reflector wrap". The origin of the drawing, posted on the internet by Greenpeace, is uncertain, and there is no accompanying explanation.<ref>[https://fas.org/sgp/eprint/morland_image037.gif The Greenpeace drawing.] {{webarchive |url=https://web.archive.org/web/20160315104941/https://fas.org/sgp/eprint/morland_image037.gif |date=March 15, 2016}} From Morland, ''Cardozo Law Review'', March 2005, p. 1378.</ref>
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)