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The Teller–Ulam design is a nuclear weapon design which is used in megaton-range thermonuclear weapons, and is more colloquially referred to as "the secret of the hydrogen bomb". It is named after two of its chief contributors, Hungarian physicist Edward Teller and Polish mathematician Stanisław Ulam, who developed the design in 1951. The idea is generally thought to pertain specifically to the use of a fission bomb "trigger" placed near an amount of fusion fuel, known as "staging", and the use of "radiation implosion" to compress the fusion fuel before igniting it. There are a number of other additions and variations to this idea posited by different sources. The first device to be based on this principle was detonated by the United States in the "Ivy Mike" nuclear test in 1952. In the Soviet Union, this design was known as Andrei Sakharov's "Third Idea". Similar devices were developed by the United Kingdom, France, China, and potentially India as well, though no specific codenames are known for their designs. Public body of knowledge concerning nuclear weapon design Detailed knowledge of actual fission and fusion weapons is classified to some degree in virtually every industrialized nation. In the United States, such "knowledge" can by default be classified as Restricted Data even if it is created by persons who are not government employees or associated with weapons programs, in a legal doctrine known as "born secret" (though the constitutional standing of the doctrine has been at times called into question, see United States v. The Progressive, et al.). Born-secret is rarely invoked for cases of private speculation. The official policy of the United States Department of Energy has been not to acknowledge the leaking of design information, as such acknowledgement would potentially validate the information as accurate. In a small number of prior cases, though (see prior restraint), the U.S. government has attempted to censor weapons information in the public press, with limited success. Though large quantities of vague data have been officially released, and larger quantities of vague data have been unofficially leaked by ex-bomb designers, most public descriptions of nuclear weapon design details rely to some degree on speculation, reverse engineering from known information, or comparison with similar fields of physics (inertial confinement fusion is the primary example). Such processes have resulted in a body of unclassified knowledge about nuclear bombs which is generally consistent with official unclassified information releases, related physics, and is thought to be internally consistent, though there are some points of interpretation which are still considered open. The state of public knowledge about the Teller–Ulam design has been most reliably shaped from a few specific incidences outlined in a section below. Basic principle
Radiation pressure The radiation pressure exerted by the large quantity of X-ray photons inside the closed casing might be enough to compress the secondary. For two thermonuclear bombs for which the general size and primary characteristics are well understood, the Ivy Mike test bomb and the modern W-80 cruise missile warhead variant of the W-61 design, the radiation pressure was calculated to be 73 million bar (atmospheres) (7.3 TPa) for the Ivy Mike design and 1,400 million bar (140 TPa) for the W-80.• Foam plasma pressure
Tamper-Pusher ablation
Comparing the implosion mechanisms Comparing the three mechanisms proposed, it can be seen that: The calculated ablation pressure is one order of magnitude greater than the higher proposed plasma pressures and nearly two orders of magnitude greater than calculated radiation pressure. No mechanism to avoid the absorption of energy into the radiation case wall and the secondary tamper has been suggested, making ablation apparently unavoidable. The other mechanisms appear to be unneeded. DOD official declassification reports indicate that foamed plastic materials are or may be used in radiation case liners, and despite the low direct plasma pressure they may be of use in delaying the ablation until energy has distributed evenly and a sufficient fraction has reached the secondary's tamper/pusher. • Proposed design variations A number of possible variations to the weapon design have been proposed: Two special variations exist which will be discussed in a further section: the cryogenically cooled liquid deuterium device used for the "Ivy Mike" test, and the putative design of the W88 nuclear warhead — a small, MIRVed version of the Teller–Ulam configuration with a prolate (egg or watermelon shaped) primary and an elliptical secondary. Most bombs do not apparently have tertiary stages — the U.S. is thought to have only produced one such model, the massive 25 Mt B41 nuclear bomb,• and the Soviet Union is thought to have used multiple stages in their 50 Mt Tsar Bomba. If any hydrogen bombs have been made from configurations other than those based on the Teller–Ulam design, the fact of it is not publicly known, with the possible exception of the Sloika design discussed below. In essence the Teller–Ulam configuration relies on at least two instances of "implosion" occurring: first, the conventional (chemical) explosives in the primary would compress the fissile core, resulting in a fission explosion many times more powerful than that which chemical explosives could achieve alone. Second, the radiation from the fissioning of the primary would be used to compress and ignite the secondary, resulting in a fusion explosion many times more powerful than the fission explosion alone. This chain of compression could be then continued with an arbitrary number of secondaries, and would end with the fissioning of the natural uranium tamper (something which could not normally be achieved without the neutron flux provided by the fusion reactions in the secondary). Such a design can be scaled up to an arbitrary strength, potentially to the level of a doomsday device (though usually such weapons are not more than a dozen megatons, which is generally considered enough to destroy even the largest practical targets). History Original "Super" The idea of a thermonuclear fusion bomb ignited by a smaller fission bomb was first proposed by Enrico Fermi to his colleague Edward Teller in 1941 at the start of what would become the Manhattan project. Teller spent most of the Manhattan Project attempting to figure out how to make the design work, to some degree neglecting his assigned work on the Manhattan Project fission bomb program. Credit controversy Stanisław Ulam, a coworker of Teller's, made the first key conceptual leaps towards a workable fusion design. Ulam's two innovations which rendered the fusion bomb practical were that compression of the thermonuclear fuel before extreme heating was a practical path towards the conditions needed for fusion, and the idea of staging or placing a separate thermonuclear component outside a fission primary component, and somehow using the primary to compress the secondary. Teller then realized that the gamma and X-ray radiation produced in the primary could transfer enough energy into the secondary to create a successful implosion and fusion burn, if the whole assembly was wrapped in a hohlraum or radiation case. Teller and his various proponents and detractors later disputed the degree to which Ulam had contributed to the theories underlying this mechanism. Testing The "George" shot of Operation Greenhouse in 1951 tested the basic concept for the first time on a very small scale, raising expectations to a near certainty that the concept would work. In November 1, 1952, the Teller–Ulam configuration was tested at full scale in the "Ivy Mike" shot at an island in the Enewetak atoll, with a yield of 10.4 megatons (over 450 times more powerful than the bomb dropped on Nagasaki during World War II). The device, dubbed the Sausage, used an extra-large fission bomb as a "trigger" and liquid deuterium—kept in its liquid state by 20 short tons (18 metric tons) of cryogenic equipment—as its fusion fuel, and weighed around 80 short tons (70 metric tons) altogether. The liquid deuterium fuel of Ivy Mike was impractical for a deployable weapon, and the next advance was to use a solid lithium deuteride fusion fuel instead. In 1954 this was tested in the "Castle Bravo" shot (the device was code-named the Shrimp), which worked far better (2.5 times) than expected and yielded 15 megatons, the largest U.S. bomb ever tested. Efforts in the United States soon shifted towards developing miniaturized Teller–Ulam weapons which could easily outfit Intercontinental Ballistic Missiles and Submarine Launched Ballistic Missiles. By 1960, with the W47 warhead• Soviet developments
British developments In 1954 work began at Aldermaston to develop the British fusion bomb, with Sir William Penny in charge of the project. British knowledge on how to make a thermonuclear fusion bomb was rudimentary, and at the time the United States was not exchanging any nuclear knowledge because of the Atomic Energy Act of 1946. However, the British were allowed to observe the American Castle tests and used sampling aircraft in the mushroom clouds, providing them with clear, direct evidence of the high compression produced in the secondary stages by radiation implosion. Because of these difficulties, in 1955 British prime minister Anthony Eden agreed to a secret plan, whereby if the Aldermaston scientists failed or were greatly delayed in developing the fusion bomb, it would be replaced by an extremely large fission bomb. In 1957 the Operation Grapple tests were carried out. The first test, Green Granite was a prototype fusion bomb, but failed to produce equivalent yields compared to the Americans and Soviets, only achieving approximately 300 kilotons. The second test Orange Herald was the modified fission bomb and produced 700 kilotons—potentially making it the largest fission explosion ever. At the time almost everyone (including the pilots of the plane that dropped it) thought that this was a fusion bomb. This bomb was put into service in 1958. A second prototype fusion bomb Purple Granite was used in the third test, but only produced approximately 150 kilotons. A second set of tests was scheduled, with testing recommencing in September 1957. The first test was based on a "… new simpler design. A two stage thermonuclear bomb which had a much more powerful trigger". This test Grapple X Round C was exploded on November 8 and yielded approximately 1.8 megatons. Two final air burst tests on September 2 and September 11, 1958, dropped bombs that yielded almost 3 megatons—Britain's most powerful tests. American observers had been invited to this second set of tests. After their successful detonation of a megaton-range device (and thus their practical understanding of the Teller–Ulam design "secret"), the United States agreed to exchange some of its nuclear designs with Great Britain, leading to the 1958 US–UK Mutual Defence Agreement. Instead of continuing with their own design, the British were given access to the design of the smaller American Mk 28 warhead and were able to manufacture copies. Other countries The details of the development of the Teller–Ulam design in other countries are less well known. The People's Republic of China detonated its first device using a Teller–Ulam design June 1967 ("Test No. 6"), a mere 32 months after detonating its first fission weapon (the shortest fission-to-fusion development yet known), with a yield of 3.3 Mt. Little is known about the Chinese thermonuclear program, however. Very little is known about the French development of the Teller–Ulam design beyond the fact that they detonated a 2.6 Mt device in the "Canopus" test in August 1968. In 1998 India claimed to detonate a "hydrogen bomb" in its Operation Shakti tests ("Shakti I", specifically), though seismographic readings have led many non-Indian experts to conclude that this is unlikely, or at least it was unlikely to have been a success as claimed, because of its low yield (claimed to be around 45 kt, though outside experts estimate it at around 30 kt, both extremely low for a successful thermonuclear detonation).• However, even low-yield tests can have a bearing on thermonuclear capability, as they can provide information on the behavior of primaries without the full ignition of secondaries.• Public knowledge The Teller–Ulam design was for many years considered one of the top nuclear secrets, and even today it is not discussed in any detail by official publications with origins "behind the fence" of classification. United States Department of Energy (DOE) policy has been, and continues to be, that they do not acknowledge when "leaks" occur, because doing such would acknowledge the accuracy of the supposed leaked information. Aside from images of the warhead casing (but never of the "physics package" itself), most information in the public domain about this design is regulated to a few terse statements by the DOE and the work of a few individual investigators. Below is a short discussion of the events which lead to the formation of these "public" models of the Teller–Ulam design, with some discussions as to their differences and disagreements with those principles outlined above. DOE statements In 1972 the DOE declassified a statement that "The fact that in thermonuclear (TN) weapons, a fission 'primary' is used to trigger a TN reaction in thermonuclear fuel referred to as a 'secondary'", and in 1979 added, "The fact that, in thermonuclear weapons, radiation from a fission explosive can be contained and used to transfer energy to compress and ignite a physically separate component containing thermonuclear fuel." To this latter sentence they specified that "Any elaboration of this statement will be classified." The only statement which may pertain to the spark plug was declassified in 1991: "Fact that fissile and/or fissionable materials are present in some secondaries, material unidentified, location unspecified, use unspecified, and weapons undesignated." In 1998 the DOE declassified the statement that "The fact that materials may be present in channels and the term 'channel filler,' with no elaboration", which may refer to the polystyrene foam (or an analogous substance).• Whether these statements vindicate some or all of the models presented above is up for interpretation, and official U.S. government releases about the technical details of nuclear weapons have been purposely equivocating in the past (see, i.e., Smyth Report). Other information, such as the types of fuel used in some of the early weapons, has been declassified, though of course precise technical information has not been. The Progressive case Progressive H-bomb cover.jpg|right|thumb|200px|Most of what is known today in the public domain about the Teller–Ulam design comes from a 1979 article in a left-wing magazine. This edition is http://progressive.org/?q=node/2252 available online. Most of the current ideas on the workings of the Teller–Ulam design came into public awareness after the DOE attempted to censor a magazine article by U.S. antiweapons activist Howard Morland in 1979 on the "secret of the hydrogen bomb". In 1978 Morland had decided that discovering and exposing this "last remaining secret" would focus attention onto the arms race and allow citizens to feel empowered to question official statements on the importance of nuclear weapons and nuclear secrecy. Most of Morland's ideas about how the weapon worked were compiled from highly accessible sources—the drawings which most inspired his approach came from none other than the Encyclopedia Americana. Morland also interviewed (often informally) many former Los Alamos scientists (including Teller and Ulam, though neither gave him any useful information), and used a variety of interpersonal strategies to encourage informational responses from them (i.e., asking questions such as "Do they still use spark plugs?" even if he was not aware what the latter term specifically referred to).•• Because the DOE sought to censor Morland's work — one of the few times they violated their usual approach of not acknowledging "secret" material which had been released — it is interpreted as being at least partially correct, though to what degree it lacks information or has incorrect information is not known with any great confidence. The difficulty which a number of nations had in developing the Teller–Ulam design (even when they apparently understood the design, such as with the United Kingdom), makes it somewhat unlikely that this simple information alone is what provides the ability to manufacture thermonuclear weapons. Nevertheless, the ideas put forward by Morland in 1979 have been the basis for all current speculation on the Teller–Ulam design. Variations There have been a few variations of the Teller–Ulam design suggested by sources claiming to have information from inside of the fence of classification. Whether these are simply different versions of the Teller–Ulam design, or should be understood as contradicting the above descriptions, is up for interpretation. Richard Rhodes "Ivy Mike" device in Dark Sun In his 1995 book Dark Sun: The Making of the Hydrogen Bomb, author Richard Rhodes describes in detail the internal components of the "Ivy Mike" Sausage device, based on information obtained from extensive interviews with the scientists and engineers who assembled it. According to Rhodes, though there was polystyrene in the "Mike" device, it was not used as a plasma source — the radiation from the primary itself was enough to compress the secondary. Whether or not this would apply only to the "Mike" device, or the Teller–Ulam design in general, is not known, and potentially casts some doubt onto the role of the foam, and to the exact mechanism of radiation "transport".• W88 revelations In 1999 a reporter for the San Jose Mercury News reported that the U.S. W88 nuclear warhead, a small MIRVed warhead used on the Trident II SLBM, had a prolate (egg or watermelon shaped) primary (code-named Komodo) and a spherical secondary (code-named Cursa) inside a specially shaped radiation case (known as the "peanut" for its shape). A story four months later in The New York Times by William Broad reported that in 1995, a supposed double agent from the People's Republic of China delivered information indicating that China knew these details about the W88 warhead as well, supposedly through espionage. (This line of investigation eventually resulted in the abortive trial of Wen Ho Lee.) If these stories are true, it would indicate a variation of the Teller–Ulam design which would allow for the miniaturization required for small MIRVed warheads. ••• The value of a prolate primary lies apparently in the fact that a MIRV warhead is limited by the diameter of the primary—if a prolate primary can be made to work properly, then the MIRV warhead can be made considerably smaller yet still deliver a high-yield explosion—a W88 warhead manages to yield up 475 kt with a physics package 1.75 m (69 in) long, with a maximum diameter of 0.55 m (22 in), and weighing probably less than 800 lb (360 kg).• Smaller warheads can allow a nation to fit more of them onto a single missile, as well as improve in more basic flight properties such as speed, mileage, and range. The calculations for a nonspherical primary are apparently orders of magnitude harder than for a spherical primary, which would likely be of interest to an existing nuclear power like the People's Republic of China (particularly as they no longer conduct nuclear testing, which would yield invaluable design information).• | |||||||||||||||
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