History of the Teller–Ulam design

History of Technical design of modern hydrogen bombs

The Teller–Ulam design is a technical concept behind modern thermonuclear weapons, also known as hydrogen bombs. The design – the details of which are military secrets and known to only a handful of major nations – is

The idea of using the energy from a fission device to begin a fusion reaction was first proposed by the Italian physicist Enrico Fermi to his colleague Edward Teller in the fall of 1941 during what would soon become the Manhattan Project, the World War II effort by the United States and United Kingdom to develop the first nuclear weapons. Teller soon was a participant at Robert Oppenheimer's 1942 summer conference on the development of a fission bomb held at the University of California, Berkeley, where he guided discussion towards the idea of creating his "Super" bomb, which would hypothetically be many times more powerful than the yet undeveloped fission weapon. Teller assumed creating the fission bomb would be nothing more than an engineering problem, and that the "Super" provided a much more interesting theoretical challenge. For the remainder of the war the effort was focused on first developing fission weapons. Nevertheless, Teller continued to pursue the "Super", to the point of neglecting work assigned to him for the fission weapon at the secret Los Alamos lab where he worked. (Much of the work Teller declined to do was given instead to Klaus Fuchs, who was later discovered to be a spy for the Soviet Union. by Teller and Ulam on March 9, 1951. The exact amount of contribution provided respectively from Ulam and Teller to what became known as the "Teller–Ulam design" is not definitively known in the public domain—the degree of credit assigned to Teller by his contemporaries is almost exactly commensurate with how well they thought of Teller in general. In an interview with Scientific American from 1999, Teller told the reporter:

<blockquote>I contributed; Ulam did not. I'm sorry I had to answer it in this abrupt way. Ulam was rightly dissatisfied with an old approach. He came to me with a part of an idea which I already had worked out and difficulty getting people to listen to. He was willing to sign a paper. When it then came to defending that paper and really putting work into it, he refused. He said, "I don't believe in it." At the Oppenheimer hearing, in 1954, Bethe spoke of Teller's “stroke of genius” in the invention of the H bomb. And finally in 1997 Bethe stated that “the crucial invention was made in 1951, by Teller.”

Other scientists (antagonistic to Teller, such as J. Carson Mark) have claimed that Teller would have never gotten any closer without the idea of Ulam. The nuclear weapons designer Ted Taylor was clear about assigning credit for the basic staging and compression ideas to Ulam, while giving Teller the credit for recognizing the critical role of radiation as opposed to hydrodynamic pressure. Priscilla Johnson McMillan in her book The Ruin of J. Robert Oppenheimer: And the Birth of the Modern Arms Race, writes that Teller sought to "conceal the role" of Ulam, and that only "radiation implosion" was Teller's idea. Teller went as far as refusing to sign the patent application because it would need Ulam's signature. Thomas Powers writes that "of course the bomb designers all knew the truth, and many considered Teller the lowest, most contemptible kind of offender in the world of science, a stealer of credit". Teller became known in the press as the "father of the hydrogen bomb", a title which he did not seek to discourage. Many of Teller's colleagues were irritated that he seemed to enjoy taking full credit for something he had only a part in, and in response, with encouragement from Enrico Fermi, Teller authored an article titled "The Work of Many People," which appeared in Science magazine in February 1955, emphasizing that he was not alone in the weapon's development (he would later write in his memoirs that he had told a "white lie" in the 1955 article, and would imply that he should receive full credit for the weapon's invention). Hans Bethe, who also participated in the hydrogen bomb project, once said, "For the sake of history, I think it is more precise to say that Ulam is the father, because he provided the seed, and Teller is the mother, because he remained with the child. As for me, I guess I am the midwife." it generated much nuclear fallout, which caused one of the worst nuclear accidents in US history after unforeseen weather patterns blew it over populated areas of the atoll and Japanese fishermen on board the Daigo Fukuryu Maru. After an initial period focused on making multi megaton hydrogen bombs, efforts in the United States shifted towards developing miniaturized Teller–Ulam weapons which could outfit Intercontinental Ballistic Missiles and Submarine Launched Ballistic Missiles. The last major design breakthrough in this respect was accomplished by the mid 1970s, when versions of the Teller–Ulam design were created which could fit on the end of a small MIRVed missile.

In the Soviet Union, the scientists working on their own hydrogen bomb project also ran into difficulties in developing a megaton range fusion weapon. Because Klaus Fuchs had only been at Los Alamos at a very early stage of the hydrogen bomb design (before the Teller–Ulam configuration had been completed), none of his espionage information was of much use, and the Soviet physicists working on the project had to develop their weapon independently. The first Soviet fusion design, developed by Andrei Sakharov and Vitaly Ginzburg in 1949 (before the Soviet Union had a working fission bomb), was dubbed the Sloika, after a Russian layered puff pastry, and was not of the Teller–Ulam configuration, but rather used alternating layers of fissile material and lithium deuteride fusion fuel spiked with tritium (this was later dubbed Sakharov's "First Idea"). Though nuclear fusion was technically achieved, it did not have the scaling property of a "staged" weapon, and their first "hydrogen bomb" test, "Joe 4" is no longer considered to be a "true" hydrogen bomb, and is rather considered a hybrid fission/fusion device more similar to a large boosted fission weapon than a Teller–Ulam weapon (though using an order of magnitude more fusion fuel than a boosted weapon). Detonated in 1953 with a yield equivalent to (only – from fusion), the Sloika device did, however, have the advantage of being a weapon which could actually be delivered to a military target, unlike the "Ivy Mike" device, though it was never widely deployed. Teller had proposed a similar design as early as 1946, dubbed the "Alarm Clock" (meant to "wake up" research into the "Super"), though it was calculated to be ultimately not worth the effort and no prototype was ever developed or tested. Attempts to use a Sloika design to achieve megaton range results proved unfeasible in the Soviet Union as it had in the calculations done in the US, but its value as a practical weapon since it was 20 times more powerful than their first fission bomb, should not be underestimated. The Soviet physicists calculated that at best the design might yield a single megaton of energy if it was pushed to its limits. After the US tested the "Ivy Mike" device in 1952, proving that a multimegaton bomb could be created, the Soviet Union searched for an additional design and continued to work on improving the Sloika (the "First Idea"). The "Second Idea", as Sakharov referred to it in his memoirs, was a previous proposal by Ginzburg in November 1948 to use lithium deuteride in the bomb, which would, by the bombardment by neutrons, produce tritium. One of the key Soviet bomb designers, Yuli Khariton, later said:

<blockquote>At that time, Soviet research was not organized on a sufficiently high level, and useful results were not obtained, although radiochemical analyses of samples of fallout could have provided some useful information about the materials used to produce the explosion. The relationship between certain short lived isotopes formed in the course of thermonuclear reactions could have made it possible to judge the degree of compression of the thermonuclear fuel, but knowing the degree of compression would not have allowed Soviet scientists to conclude exactly how the exploded device had been made, and it would not have revealed its design. and nearly reached as high as the altitude of the deploying Tu 95 bomber. The RDS 220 test demonstrated how "staging" could be used to develop arbitrarily powerful weapons.]] Sakharov stated in his memoirs that though he and Davidenko had fallout dust in cardboard boxes several days after the "Mike" test with the hope of analyzing it for information, a chemist at Arzamas 16 (the Soviet weapons laboratory) had mistakenly poured the concentrate down the drain before it could be analyzed. Only in the fall of 1952 did the Soviet Union set up an organized system for monitoring fallout data. Nonetheless, the memoirs also say that the yield from one of the American tests, which became an international incident involving Japan, told Sakharov that the US design was much better than theirs, and he decided that they must have exploded a separate fission bomb and somehow used its energy to compress the lithium deuteride. He then turned his focus to finding a way for an explosion to one side to be used to compress the ball of fusion fuel within of symmetry, which he realised could be achieved by focusing the X rays.

Very little is known about the French development of the Teller–Ulam design beyond the fact that it detonated a 2.6 Mt device in the "Canopus" test in August 1968.

On 11 May 1998, India announced that it has detonated a hydrogen bomb in its Operation Shakti tests ("Shakti I", specifically). Some non Indian analysts, using seismographic readings, have suggested that it might not be the case by pointing at the low yield of the test, which they say is close to 30 kilotons (as opposed to 45 kilotons announced by India). However, some non Indian experts agree with India. Dr. Harold M. Agnew, former director of the Los Alamos National Laboratory, said that India's assertion of having detonated a staged thermonuclear bomb was believable. The British seismologist Roger Clarke argued that seismic magnitudes suggested a combined yield of up to 60 kilotonnes, consistent with the Indian announced total yield of 56 kilotonnes. Professor Jack Evernden, a US seismologist, has always maintained that for correct estimation of yields, one should "account properly for geological and seismological differences between test sites." His estimation of the yields of the Indian tests concur with those of India. Indian scientists have argued that some international estimations of the yields of India's nuclear tests are unscientific. India says that the yield of its tests were deliberately kept low to avoid civilian damage and that it can build staged thermonuclear weapons of various yields up to around 200 kilotons on the basis of those tests.

North Korea claimed to have tested its miniaturised thermonuclear bomb on January 6, 2016. North Korea's first three nuclear tests (2006, 2009 and 2013) had a relatively low yield and do not appear to have been of a thermonuclear weapon design. In 2013, the South Korean Defense Ministry had speculated that North Korea might be trying to develop a "hydrogen bomb" and such a device might be North Korea's next weapons test. In January 2016, North Korea claimed to have successfully tested a hydrogen bomb, but only a magnitude 5.1 seismic event was detected at the time of the test, a similar magnitude to the 2013 test of a 6–9 kt atomic bomb. Those seismic recordings have scientists worldwide doubting North Korea's claim that a hydrogen bomb was tested and suggest it was a non fusion nuclear test. On September 9, 2016, North Korea conducted their fifth nuclear test which yielded between 10 and 30 kilotons. On September 3, 2017, North Korea conducted a sixth nuclear test just a few hours after photographs of North Korean leader Kim Jong un inspecting a device resembling a thermonuclear weapon warhead were released. Initial estimates in first few days were between 70 and 160 kilotons and were raised over a week later to range of 250 to over 300 kilotons. Jane's Information Group estimated, based mainly on visual analysis of propaganda pictures, that the bomb might weigh between .

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. The policy of the US Department of Energy (DOE) has always been not to acknowledge when "leaks" occur since 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 the design is relegated to a few terse statements and the work of a few individual investigators. Here is a short discussion of the events that led to the formation of the "public" models of the Teller–Ulam design, with some discussions as to their differences and disagreements with those principles outlined above.

The general principles of the "classical Super" design were public knowledge even before thermonuclear weapons were first tested. After Truman ordered the crash program to develop the hydrogen bomb in January 1950, the Boston Daily Globe published a cutaway description of a hypothetical hydrogen bomb with the caption Artist's conception of how H bomb might work using atomic bomb as a mere "trigger" to generate enough heat to set up the H bomb's "thermonuclear fusion" process. The fact that a large proportion of the yield of a thermonuclear device stems from the fission of a uranium 238 tamper (fission fusion fission principle) was revealed when the Castle Bravo test "ran away," producing a much higher yield than originally estimated and creating large amounts of nuclear fallout. In 1981, Morland published a book, The secret that exploded, about his experience, describing in detail the train of thought which led him to his conclusions about the "secret." Because the DOE sought to censor Morland's work, one of the few times that it violated its usual approach of not acknowledging "secret" material that had been released, it is interpreted as being at least partially correct, but 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 understood the design, such as with the United Kingdom) makes it somewhat unlikely that the 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.