The Teller–Ulam design is the technical concept behind thermonuclear weapons, also known as hydrogen bombs. The design relies on the radiation implosion principle, using thermal X-rays released from a fission nuclear primary to compress and ignite nuclear fusion in a secondary. This is in contrast to the simpler design and usage of nuclear fusion in boosted fission weapons.
The design is named for scientists Edward Teller and Stanisław Ulam, who originally devised the concept in January 1951 for the United States nuclear weapons program, though their individual roles have been subsequently debated. The US Greenhouse George test in May 1951, the world's first artificial thermonuclear fusion, validated the radiation implosion principle. The US first tested the "true" Teller-Ulam design with the very high-yield Ivy Mike test in 1952.
The design was independently devised and then tested by teams of nuclear weapons scientists working for at least four more governments: the Soviet Union in 1955 (RDS-37), the United Kingdom in 1957 (Operation Grapple), China in 1966 (629), and France in 1968 (Canopus). There is not enough public information to determine whether India, Israel, or North Korea possess multi-stage weapons. Pakistan is not considered to have developed them. The Teller-Ulam design is the basis for all nuclear weapons tests above one megaton yield.
History Teller's "Super"
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 late 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 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.) Teller was given some resources with which to study the "Super", and contacted his friend Maria Göppert-Mayer to help with laborious calculations relating to opacity. The "Super", however, proved elusive, and the calculations were difficult to perform. The properties of fission and fusion reactions could be studied by cyclotrons. The propagation of a fission detonation could be studied with the help of reactor and critical assembly experiments. But thermonuclear fusion and the extreme case of plasma ignition, were only considered achievable by a nuclear test (ultimately Greenhouse George), for which the justification was lacking. In the meantime, research proceeded via slow manual calculations and the early computer ENIAC.
Even though they had witnessed the Trinity test, after the atomic bombings of Japan scientists at Los Alamos were surprised by how devastating the effects of the weapon had been. Many of the scientists rebelled against the notion of creating a weapon thousands of times more powerful than the first atomic bombs. For the scientists the question was in part technical—the weapon design was still quite uncertain and unworkable—and in part moral: such a weapon, they argued, could only be used against large civilian populations, and could thus only be used as a weapon of genocide. Many scientists, such as Teller's colleague Hans Bethe (who had discovered stellar nucleosynthesis, the nuclear fusion that takes place in stars), urged that the United States should not develop such weapons and set an example towards the Soviet Union. Promoters of the weapon, including Teller and Berkeley physicists Ernest Lawrence and Luis Alvarez, argued that such a development was inevitable, and to deny such protection to the people of the United States—especially when the Soviet Union was likely to create such a weapon itself—was itself an immoral and unwise act. Still others, such as Oppenheimer, simply thought that the existing stockpile of fissile material was better spent in attempting to develop a large arsenal of tactical atomic weapons rather than potentially squandered on the development of a few massive "Supers".
In any case, work slowed greatly at Los Alamos, as some 5,500 of the 7,100 scientists and related staff who had been there at the conclusion of the war left to go back to their previous positions at universities and laboratories. A conference was held at Los Alamos in 1946 to examine the feasibility of building a Super; it concluded that it was feasible, but there were a number of dissenters to that conclusion.
When the Soviet Union exploded their own atomic bomb (dubbed "Joe 1" by the US) in August 1949, it caught Western analysts off guard, and over the next several months there was an intense debate within the US government, military, and scientific communities on whether to proceed with the far-more-powerful Super. On January 31, 1950, US President Harry S. Truman ordered a program to develop a hydrogen bomb.
Many scientists returned to Los Alamos to work on the "Super" program, but the initial attempts still seemed highly unworkable. In the "classical Super," it was thought that the heat alone from the fission bomb would be used to ignite the fusion material, but that proved to be impossible. For a while, many scientists thought (and hoped) that the weapon itself would be impossible to construct.
Ulam's and Teller's contributions
The exact history of the Teller–Ulam breakthrough is not completely known, partly because of numerous conflicting personal accounts and also by the continued classification of documents that would reveal which was closer to the truth. Previous models of the "Super" had apparently placed the fusion fuel either surrounding the fission "trigger" (in a spherical formation) or at the heart of it (similar to a "boosted" weapon) in the hopes that the closer the fuel was to the fission explosion, the higher the chance it would ignite the fusion fuel by the sheer force of the heat generated.
In 1951, after many years of fruitless labor on the "Super", a breakthrough idea from the Polish émigré mathematician Stanislaw Ulam was seized upon by Teller and developed into the first workable design for a megaton-range hydrogen bomb. This concept, now called "staged implosion" was first proposed in a classified scientific paper, On Heterocatalytic Detonations I. Hydrodynamic Lenses and Radiation MirrorsThe term "heterocatalytic" was Teller and Ulam's jargon for their new idea; using an atomic explosion to ignite a secondary explosion in a mass of fuel located outside the initiating bomb. This is the original classified paper by Teller and Ulam proposing staged implosion. This declassified version is heavily redacted, leaving only a few paragraphs. 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:
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."
The issue is controversial. Bethe in his “Memorandum on the History of the Thermonuclear Program” (1952) cited Teller as the discoverer of an “entirely new approach to thermonuclear reactions”, which “was a matter of inspiration” and was “therefore, unpredictable” and “largely accidental.” 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.” * H.A. Bethe, " J. Robert Oppenheimer 1904–1967," National Academy of Sciences of the United States of America Biographical Memoirs (1997, vol. 71, pp. 175–218; on 197)
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)."Edward Teller's Memoirs: a book review by S. Uchii", PHS Newsletter (Philosophy and History of Science, Kyoto University), no. 52, July 22, 2003 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."