Editing Nuclear weapon design (section)

===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 – 1151 Nuclear Weapon Data – 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>