Understandably, for a few weeks organizing the project took as much time as doing physics. Wheeler led the recruitment of young physicists to augment Toll and me. Toll served as Wheeler’s general deputy (his “strong right arm”{1}). Toll’s “people skills” and talent for administration were already evident. As I recall, Toll also arranged for security to be put in place. That meant locked filing cabinets and round-the-clock guards. I was assigned the task of finding secretaries and human “computers.” Because I had never done anything of the kind before and was intrigued by new challenges, I plunged into that task and quickly found and hired half a dozen well qualified young people—all female, as it turned out. The picture on this page shows most of the Matterhorn B team in 1952, support staff in front, scientists behind. The gender imbalance is evident.
I was also dispatched to the Princeton Post Office to get a Post Office Box number for Matterhorn (B and S combined). We were assigned P. O. Box 451. If you go now to the Web site of the Princeton Plasma Physics Laboratory, you will find, more than half a century later, that its mailing address is P.O. Box 451.
When Matterhorn was conceived, there was no Teller-Ulam idea. A few months later, when Matterhorn set up shop and got to work, the Teller-Ulam idea of radiation implosion was the clear choice for the path ahead. Yet, in May and June 1951, there was no specific, well-defined design for the device to be tested the next year. We just had the general idea that a cylinder of thermonuclear fuel—either deuterium or lithium-6 deuteride—would be compressed and would, we hoped, ignite and burn. Even without a design, we could also assume that the cylinder holding the fuel would be made of uranium—ordinary uranium, consisting largely of U238, not the rare, expensive isotope U235 used in some fission bombs (I say “some” fission bombs because plutonium-239 was—and is—also a common component of fission bombs). The reason for this assumed choice of container was that neutrons generated in thermonuclear burning—especially the 14-MeV neutrons created in the DT reaction (see page 110)—are energetic enough to cause even U238 to undergo fission, so the container itself would be another “bomb,” adding greatly to the energy released. Uranium was therefore the clearly preferred choice over steel or any other material to house the thermonuclear fuel.
Also, even without a specific design, there was an obvious way to divide up the work. The device would have to consist of a fission bomb to provide the initial jolt of radiation, a cylinder of thermonuclear fuel to provide the fusion energy (and a lot more neutrons), and a connecting structure and radiation channel between the two. In short, a three-stage device: a fission component, a link, and a fusion component (with a good deal of fission also showing up in that third component). The scientists at Los Alamos, with already half a dozen years of experience in designing fission bombs of various sizes and types, were clearly better qualified than any of us at Matterhorn to work on the fission bomb part of the design. They, along with their engineer colleagues at Los Alamos, were also better able to deal with the connecting link and radiation channel, however that might turn out to be configured. Wheeler and Toll and I, during our time in Los Alamos, had worked almost exclusively on thermonuclear burning—mostly in the context of the classical Super, but also specifically on the George and Item tests at Greenhouse (fired in May 1951). For that reason and because of the small size of the Matterhorn group, the Princeton end of the theoretical physics axis was logically assigned responsibility for calculations and design bearing on the fusion end of the device.
Of course, in reality, neither the work nor the device itself could be so neatly compartmentalized. It was a single, interconnected device. And it was a single, interconnected team. During the course of the 1951-52 year, we in Princeton kept in close, regular touch with our Los Alamos colleagues and made some trips to meet with them in person. (I remember one such trip when Wheeler telephoned Pennsylvania Railroad headquarters in New York City and explained why it would be in the national interest for the Broadway Limited to make an unscheduled stop in Princeton Junction to pick up some Matterhorn scientists bound for New Mexico. When that train did stop for us, the conductor, assuming that nothing less than college athletics could account for such an unusual event, asked if we were the Princeton basketball team and John Wheeler was our coach. A few of us were of above average height.)
Since the trip from Princeton to Lamy (the station serving Santa Fe) entailed a change of trains in Chicago,[72] it afforded the opportunity for us to meet with Edward Teller, which we did at least once in the fall of 1951. He had decamped from Los Alamos in September, returning to his professorship at the University of Chicago, irritated with Los Alamos management but quite eager to be briefed on what we were up to and to make suggestions.
From the summer of 1950 through the summer of 1952, first from a Los Alamos base, then from a Princeton base, much of my own effort was devoted to programming and computing nuclear reactions and nuclear energy release—from both fusion reactions and secondary fission reactions. At the beginning of that two-year period, the resources I had available were a slide rule, a desk calculator, and Los Alamos’s human “computers.” Soon added were IBM card-programmed calculators (CPCs), which I used in Los Alamos, at Sandia Laboratories in Albuquerque, and in an IBM building in New York City. At the end of that two-year period, I was working with the SEAC computer at the National Bureau of Standards in Washington, D.C. In the summer of 1952, the SEAC (Standards Eastern Automatic Computer) was probably the finest computer in the world—although its memory capacity and its speed fell far short or what is today available in the dullest of smart phones. The SEAC’s granddaddy, the ENIAC, was by then obsolete. The SEAC’s immediate progenitor, the MANIAC at the Institute of Advanced Study, was in principle superior but in 1952 was still too error-prone to compete seriously with the SEAC. In Chapter 15 I discuss my many all-night shifts on the SEAC.
Most of our early calculating was on so-called “one-dimensional” configurations. Although the device was, of course, three-dimensional, limitations of computing power forced us to track changes of conditions along only one dimension, either “axially” or “radially.” We sought to learn if a charge of thermonuclear fuel, heated to a certain temperature and squeezed to a certain density and pressure, could “burn” steadily down the length of a cylinder after being ignited at one end, or could burn outward from its center toward its encircling container without fizzling. One needed to keep track of a set of variable quantities such as temperature, pressure, number of deuterons per unit volume, radial distance to the container wall, speed of propagation of the flame, rates of energy release in the thermonuclear material[73] and in the uranium wall, etc. Each of these quantities depends on all the others. Putting their interrelationships into mathematical form leads to what are called coupled differential equations. The basic equations don’t change as the computing power increases. What changes is how many simplifying assumptions one has to make, what factors one decides to ignore, by what time interval one jumps from one moment to the next, how finely one divides up space, and so on. The goal is to complete a meaningful calculation in a reasonable time, given the computer’s limitations of memory and speed. (The human computer had a limitation only of speed, not “memory,” since paper was plentiful.)
72
Although not a change of car. Our sleeper was disconnected from the Pennsylvania Railroad Broadway Limited and connected to the Santa Fe Chief or Super Chief for departure a few hours later.
73
Adding to the complexity is the fact that some of the energy released in one place is carried by neutrons to some other place. By contrast, in chemical combustion, all of the energy released in one place is deposited at that place.