Editing Soviet atomic bomb project (section)

== Initial design of thermonuclear weapons ==
{{main|Tsar Bomba|Thermonuclear weapon}}
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[[File:Размещение кораблей при опыте 21 сентября 1955 года.svg|thumb|250px|left|{{small|The Russian language data studying the placement of Soviet warships to measure the [[Shock waves|(blast) ranges]] of their thermonuclear devices in 1955.}}]]

Early ideas of the thermonuclear bomb came from the Russian espionages in the United States, and the internal Soviet studies. Though the espionage did help the Soviet studies, the early American thermonuclear designs and [[Thermonuclear weapon|concepts]] had substantial flaws, so it may have confused, rather than assisted, the Soviet effort to achieve the nuclear capability.<ref>{{Cite book|title=Beginnings of the Soviet H-Bomb Program|last=Goncharov}}</ref> The designers of the early thermonuclear bombs envisioned using an atomic bomb as a trigger to provide the needed heat and compression to initiate the thermonuclear reaction in a layer of liquid deuterium between the fissile material and the surrounding chemical high explosive.<ref name=":0">{{Cite book|title=The Kremlin's Nuclear Sword: The Rise and Fall of Russia's Strategic Nuclear Forces|last=Zaloga|first=Steve|publisher=Smithsonian Books|year=2002|pages=32–35}}</ref> The group would realize that a lack of sufficient heat and compression of the deuterium would result in an insignificant fusion of the deuterium fuel.<ref name=":0" />

The [[Andrei Sakharov]]'s study group at FIAN in 1948 came up with a second concept in which adding a shell of natural, unenriched uranium around the deuterium would increase the deuterium concentration at the uranium-deuterium boundary and the overall yield of the device, because the natural uranium would capture neutrons and itself fission as part of the thermonuclear reaction. This idea of a layered fission-fusion-fission bomb led Sakharov to call it the sloika, or layered cake.<ref name=":0" /> 

It was also known as the RDS-6S, or Second Idea Bomb.<ref>The American counterpart to this idea was Edward Teller's Alarm Clock design of August 1946. In August 1990 the Soviet science journal Priroda published a special issue devoted to Andrei Sakharov, which contained more detailed notes on the early fusion bomb than Sakharov's own memoirs, especially the articles by V.E. Ritus and Yu A. Romanov</ref> This second bomb idea was not a fully evolved thermonuclear bomb in the contemporary sense, but a crucial step between pure fission bombs and the thermonuclear "supers".<ref>{{Cite book|title=Beginnings|last=Goncharov|pages=50–54}}</ref> Due to the three-year lag in making the key breakthrough of radiation compression from the United States the Soviet Union's development efforts followed a different course of action. In the United States they decided to skip the single-stage fusion bomb and make a two-stage fusion bomb as their main effort.<ref name=":0" /><ref>The Super Oralloy bomb was developed in Los Alamos and tested on 15 November 1952</ref> Unlike the Soviet Union, the analog RDS-7 advanced fission bomb was not further developed, and instead, the single-stage 400-kiloton RDS-6S was the Soviet's bomb of choice.<ref name=":0" />

The RDS-6S Layer Cake design was detonated on 12 August 1953, in a test given the code name by the Allies of "[[Joe 4]]".<ref>[https://www.atomicheritage.org/history/soviet-hydrogen-bomb-program Soviet Hydrogen Bomb Program], Atomic Heritage Foundation, August 8, 2014.  Retrieved 28 March 2019.</ref> The test produced a yield of 400 kilotons, about ten times more powerful than any previous Soviet test. Around this time the United States detonated its first super using radiation compression on 1 November 1952, [[Ivy Mike|code-named Mike]]. Though the Mike was about twenty times greater than the RDS-6S, it was not a design that was practical to use, unlike the RDS-6S.<ref name=":0" />

Following the successful launching of the [[RDS-6s]], Sakharov proposed an upgraded version called RDS-6sD.<ref name=":0" /> This bomb was proved to be faulty, and it was neither built nor tested. The Soviet team had been working on the RDS-6t concept, but it also proved to be a dead end.

In 1954, Sakharov worked on a third concept, a two-stage thermonuclear bomb.<ref name=":0" /> The third idea used the radiation wave of a fission bomb, not simply heat and compression, to ignite the fusion reaction, and paralleled the discovery made by Ulam and Teller. Unlike the RDS-6s boosted bomb, which placed the fusion fuel inside the primary A-bomb trigger, the thermonuclear super placed the fusion fuel in a secondary structure a small distance from the A-bomb trigger, where it was compressed and ignited by the A-bomb's X-ray radiation.<ref name=":0" /> The [[KB-11]] Scientific-Technical Council approved plans to proceed with the design on 24 December 1954. Technical specifications for the new bomb were completed on 3 February 1955, and it was designated the [[RDS-37]].<ref name=":0" />

The RDS-37 was successfully tested on 22 November 1955 with a yield of 1.6 megaton. The yield was almost a hundred times greater than the first Soviet atomic bomb six years before, showing that the Soviet Union could compete with the United States,<ref name=":0" /><ref>Details of Soviet weapons designs after 1956–57 are generally lacking. A certain amount can be inferred from data about missile warheads, and in recent histories, the two nuclear-warhead development bureaus have begun to cautiously reveal which weapons they designed,</ref> and would even [[Tsar Bomba|exceed them]] in time.