[the helium isotopes] He3, He4, and other nuclei, together with the increasing density of neutrons of varied and variable energies in this “gas” influences directly the changing rate of the reaction; and it does so also by changing the values of the density and temperature. Simultaneously, the radiation field is increasingly present and influences, in its turn, the motion of the material.
“The work of the ‘Super’ group on the visualization and on quantitative following of these processes,” Ulam concludes, “constituted a veritable monument to the imagination and skill of theoreticians —”
It had been possible to develop a crude mathematical model of implosion during the war using desktop mechanical calculating machines and IBM punch-card sorters. The Super calculations that Teller's group needed to do exceeded the capabilities of such machines. Here John von Neumann, one of the great mathematicians of the twentieth century, intervened creatively. Von Neumann, a prodigy who could recite whole chapters verbatim of books that he had read only once and a lightning mental calculator, had taken up theoretical physics as a sideline before the Second World War and had made himself an expert on shock and detonation waves. “The story used to be told about him at Princeton,” writes a colleague, Herman Gold-stine, “that while he was indeed a demi-god he had made a detailed study of humans and could imitate them perfectly. Actually he had great social presence, a very warm, human personality, and a wonderful sense of humor.” It was von Neumann who had calculated the complex shape of the high-explosive lenses in the Fat Man bomb.
In 1944, Goldstine and a small group of engineers at the University of Pennsylvania's Moore School of Engineering had been building a new type of calculating machine with government funding that used vacuum tubes rather than gears to run calculations. They called it the ENIAC, an acronym that summarized its functions as an electronic numerical integrator and computer. “Sometime in the summer,” Goldstine remembers, “… I was waiting for a train to Philadelphia on the railroad platform in Aberdeen [Maryland, the location of the US Army's Aberdeen Proving Ground] when along came von Neumann.” The Penn mathematician had never met his legendary colleague. “It was therefore with considerable temerity that I approached this world-famous figure, introduced myself and started talking… The conversation soon turned to my work. When it became clear to von Neumann that I was concerned with the development of an electronic computer capable of 333 multiplications per second, the whole atmosphere of our conversation changed from one of relaxed good humor to one more like the oral examination for the doctor's degree in mathematics. Soon thereafter the two of us went to Philadelphia so that von Neumann could see the ENIAC.”
It was just what von Neumann and Los Alamos had been looking for. The Hungarian-born mathematician embraced the machine and the concept of the machine, and soon abstracted from its crude vacuum-tube technology a logical system for manipulating and processing information, mathematical or otherwise. Goldstine believes von Neumann's 101-page draft report, written that final winter and spring of the war, was “the most important document ever written on computing and computers.” The ENIAC as the Moore School group had designed it had to be prepared for each new problem by physically rearranging its circuit wires, plugging and unplugging what looked like old-fashioned telephone switchboards. In his draft report, von Neumann formulated for the first time the idea of a stored operating program — and defined in the process the basic organization of the digital computer: “The logical control of the device, that is, the proper sequencing of its operations, can be most efficiently carried out by a central control organ. If the device is to be…
The first problem assigned to the first working electronic digital computer in the world was the hydrogen bomb. Los Alamos mathematician Nicholas Metropolis (writing in the third person) recalled participating in the breakthrough:
In early 1945, as the construction of the ENIAC was nearing completion, von Neumann raised the question with [physicist Stanley] Frankel and Metropolis of using it to perform the very complex calculations involved in hydrogen bomb design. The response was immediate and enthusiastic. Arrangements were made by von Neumann on the basis that the “Los Alamos problem” would provide a much more severe challenge to the ENIAC on its shakedown trial…
The ENIAC ran a first rough version of the thermonuclear calculations for six weeks in December 1945 and January 1946. Los Alamos prepared a half million punched cards of data, enough to keep a hundred people busy for a year at mechanical desktop machines.
The outcome appeared promising, writes Ulam:
It seemed at that time that the feasibility of the thermonuclear bomb was established, according to the opinion of the author [i.e., Ulam]. Even though the work was of necessity incomplete, and had to omit certain physical effects, the results of the calculations had great importance in leaving open the hopes for a successful solution to the problem and the eventual construction of an H-bomb. One could hardly exaggerate the psychological importance of this work and the influence of these results on Teller himself and on people in the Los Alamos laboratory in general… I well remember the spirit of exploration and of belief in the possibility of getting trustworthy answers in the future. This [was] partly because of the existence of computing machines which could perform much more detailed analysis and modeling of physical problems.
Los Alamos published a
To review wartime work on the Super and to propose a course of further studies, Los Alamos scheduled a secret three-day conference for April 18–20, 1946. Just before the conference began, the laboratory issued its first major technical report on the thermonuclear,
Along with Teller, Konopinski, Philip Morrison, von Neumann, Canadian theoretician J. Carson Mark, Metropolis, Robert Serber, Ulam and twenty-three other scientists, Klaus Fuchs attended the April Super Conference. On the first morning, in Norris Bradbury's office, the group heard Edward Teller review the prima facie arguments of the April 15 technical report and then describe his proposed design. It came to be called the “Super” and the “classical Super” to distinguish it from the booster and other, later designs. Its configuration has never been made public in detail, but Carson Mark, who took over direction of the theoretical division at Los Alamos after the war, outlined it in an interview:
The classical Super was the idea that deuterium could be set burning if you got it hot enough and [that] perhaps… a fission bomb might provide the sort of temperature level that you would need. So we have long pipe full of liquid deuterium and we have a fission bomb which we set off at one end of it with the idea that we will heat that end sufficiently that a burning wave will get started and proceed along the pipe. The burning wave being a deuterium reaction. Now there is the classical Super. There are some answers that have to be filled in. Amongst them, if you heat one end of a deuterium pipe like that, will a burning wave in fact run along it that will detonate like a stick of high explosives? That's a central question. Of course you would have to ask, how hot do I have to make it before that will happen, but even if I make it very hot, [you would have to ask]
An important difference between a fission bomb and a thermonuclear bomb was that except in its fission
