Classical Super / Runaway Super

In the fall of 1941, Enrico Fermi suggested that a fission bomb be used to heat a mass of deuterium to a temperature where the thermonuclear fusion of two deuterium atoms will proceed rapidly. Teller came up with a counter argument: that the needed temperature would be so high that most energy will appear as useless radiation rather than usable kinetic energy of the nuclei. Fermi agreed to Teller's objection. The concept stalled Teller thought his calculations indicated the unlikelihood of a fission weapon producing the hundreds of millions of degrees of temperature needed to trigger significant fusion.

A few months later, Teller attempted to finalize Teller's argument on the deuterium-plus-deuterium reaction. Teller did not succeed. Emil Konopinski, Teller's collaborator, suggested (correctly) that tritium in a deuterium-plus-tritium reaction might react much faster than deuterium-plus-deuterium. Teller, in turn, proposed that the thermonuclear reaction might proceed before a lot of radiation is emitted and an equilibrium with radiation is established. The thermonuclear superbomb became a secondary endeavor during the Manhattan Project.

During this work, Oppenheimer invited Teller and his colleagues to participate in a discussion at Berkeley about the problems of explosives using nuclear energy. Oppenheimer mentioned the possibility of a hydrogen bomb to Arthur Compton (head of the whole Chicago project), arguing that the fission and fusion bomb problems required a new laboratory, which was established in March 1943.

The design adopted for the first hydrogen bomb did not come easily or quickly. Unlike fission weapons, scientists did not have a clear idea of the range of physical constraints governing thermonuclear weapon design. Extensive mathematical modeling and simulation were required. The need for better and better computers was compelling. During World War II, all computing at Los Alamos was done with desktop calculators and a variety of IBM business machines. Such machines were not capable of handling the complex modeling required for developing the hydrogen bomb.

The distinguished mathematician John von Neumann first advised Los Alamos scientists of the ENIAC (electronic numerical integrator and calculator) project at the University of Pennsylvania. The goal of the project, supported by the US Army Ballistics Research Laboratory in Aberdeen, Maryland, was to create a computing machine to solve ballistic trajectory problems. The ENIAC at the University of Pennsylvania was programmed by interconnecting the electron tube registers with cables inserted in plug boards.

Even before the Trinity test, as the ENIAC was nearing completion in early 1945, von Neumann raised the question with Frankel and Metropolis of using the ENIAC to compute the first set of problems on thermonuclear designs. The response was immediate and enthusiastic. Arrangements were made by von Neumann, who was also a consultant to Aberdeen, using the argument that the "Los Alamos Problem" was a more comprehensive test of the computer since its complexity was at least an order of magnitude greater than the computation of firing tables.

The experience of using the ENIAC, which occurred at about the same time as the Trinity test, was, for the participants, as memorable as that of the first atomic explosion. Electronic equipment, bristling with 18,000 electron tubes and a half-million solder joints, filled one large room and was joined together to operate as a single unit. Attending this equipment was a cadre of very earnest people who wanted the machine to give real answers to real problems, and their immersion in electronic computing was total. The computer age had begun in earnest.

In Los Alamos, difficulties connected with the fission bomb soon required the whole available effort. But working with a small group, Teller could give continued attention to the hydrogen bomb. It turned out that it is quite difficult to postpone radiation equilibrium and obtain sufficient time for thermonuclear reactions. But it still seemed quite promising to obtain a hydrogen bomb in this manner. With the end of the Second World War, strong feelings developed against continuing the work. Teller returned to pure physics in Chicago for the next few years, which personally Teller found more attractive.

Beginning shortly after the war, true computers started to become available, beginning with the ENIAC, IBM's SSEC, and the National Bureau of Standards SEAC. Because these machines were on the East Coast, many of the thermonuclear calculations actually took place far from Los Alamos. Although the first hydrogen bomb could have been developed without modern computers, such development would have been substantially delayed.

In the spring of 1946, when the series of ENIAC computations of one-dimensional thermonuclear burning of deuterium and tritium had been completed, a conference was held in Los Alamos. It was organized by Edward Teller with, among others, Enrico Fermi and John von Neumann participating. The principal purpose was to discuss the computational results and to assess the prospects for a physical realization of a thermonuclear device. Despite the simplified but nonetheless relatively ambitious nature of the model, the general consensus was that the preliminary results were encouraging. Several comprehensive documents were prepared as the first phase of the Los Alamos project came to a close.

By the summer of 1946, the a number of basic facts on thermonuclear reactions appeared to have been established by the work of Teller's group during and after the war. In a sufficiently rich mixture of T and D, a reaction could take place and could propagate, given sufficient initial temperature. A self-sustaining and propagating reaction in pure liquid deuterium seemed a likely possibility. If successful, such a reaction could deliver energies equivalent to 1000 fission bombs and more, from a device weighing not much more than an ordinary fission bomb and containing mainly cheap materials. To initiate a reaction in deuterium, mixtures of deuterium and tritium were useful, and it was believed that relatively modest amounts of deuterium might be sufficient for the purpose. The initial heating of the T-D mixture to the required temperature appeared perhaps as the most difficult task because it was questionable whether fission bombs of sufficient yield could be constructed. Later calculations demonstrated that the "runaway super" as conceived in 1946 was not feasible, certainly was impractical.

At this point it was believed that the Super could be ignited with less than 200 grams of tritium. Energy was transferred by high-energy neutrons, spawned by triton-deuteron or deuteron-deuteron fusions. These neutrons, colliding with deuterium nuclei, transfer some of their kinetic energy to the impacted deuterons. This D-D reaction was expected to be self-propagating, without compression.

The Classical Super was based on the belief that a flow of neutrons generated in a primary gun-type uranium-235 bomb could ignite a nuclear detonation in a long cylinder filled with liquid deuterium (by means of an intermediate chamber filled with a D± T mixture). The bomb would burn about a cubic meter of deuterium, releasing energy equivalent to that of about 10 megatons. The probable weight of a fission-fusion device of this design was estimated at around 10 tons.

The general belief of those working on the problem at that time, however, was that some such design could be made to detonate, although it was fully understood that much study would yet be required to establish this fact and determine the most favorable pattern.

The requirements for materials, engineering developments, and more detailed understanding of basic physical processes were impressive, and would necessarily involve a considerable fraction of the resources which are likely to be devoted to work on atomic developments in the next years. An active program to realize such a device was then thought to require amounts of tritium beyond the reach of the Hanford plant to produce in any relevant time, so that the building of a reactor for tritium production was probably involved.

The Classical Super design was based on what happens in a supernova. A boosted trigger is surrounded by a mass of fusion fuel. When the trigger goes off, the heat and shockwave would set off an outwardly propagating thermonuclear reaction in the fusion material. But calculations by Ulam and von Neumann demonstrated that the temperatures and pressures insufficient to sustain the reaction, which would fizzle.