In 1951 Dick Garwin came for his second summer to Los Alamos. He was then twenty-three and two years past his Ph.D.[75] Edward Teller, having interacted with Garwin at the University of Chicago, knew him to be an extraordinarily gifted experimental physicist as well as a very talented theorist. He knew, too, that Fermi had called Garwin the best graduate student he ever had.{5} So when Garwin came to Teller shortly after arriving in Los Alamos that summer (probably in June 1951) asking him “what was new,”{6} Teller was ready to pounce. He referred Garwin to the Teller-Ulam report of that March and then asked him to “devise an experiment that would be absolutely persuasive that this would really work.” Garwin set about doing exactly that and in a report dated July 25, 1951, titled “Some Preliminary Indications of the Shape and Construction of a Sausage, Based on Ideas Prevailing in July 1951,”{7} he laid out a design with full specifics of size, shape, and composition, for what would be the Mike shot fired the next year.
Garwin then presented his design to the Lab committee overseeing thermonuclear developments, a committee chaired that summer by Hans Bethe, visiting from Cornell. (This may have been an interim committee functioning between the Family Committee and the Theoretical Megaton Group).[76] Bethe, an eminence in the physics world whose words were seldom questioned, said that he thought the walls of the outer casing in Garwin’s design were not thick enough. Garwin, to the astonishment of some who were present, said, in effect, “You are wrong, Hans, and here’s why.” Bethe admitted the soundness of Garwin’s argument, and the design was approved.{9} From then on, we at Matterhorn, as well as the fission-bomb designers at Los Alamos and a slew of other specialists, knew what we had to work with.
Regarding Teller’s faith in the young, I must relate one example in which I played a part. Some time in early 1951 Teller came to me holding what looked like a thick report in his hand. “Ken,” he said, “I am getting redder [with embarrassment] by the microsecond. I have this draft dissertation from my student in Chicago, and I haven’t had time to read it. Would you please read it and tell me what you think.” I read it with care. It was a thorough discussion of a proposed experiment to search for the hypothetical magnetic monopole. (A monopole is a particle analogous to an electron that carries magnetic instead of electric charge. By chance, as I related in Chapter 11, I had done some theoretical work on the behavior of this supposed entity. To date there have been many searches for it and no sightings.) I found the dissertation to be admirably clear, and free of any errors so far as I could tell. I reported this to Teller and he then notified the student of his approval (no doubt after examining the dissertation himself).
What is the Garwin design? What is a “sausage”? The second question first. The outer steel capsule containing the entire device had a length about three times its diameter, so it roughly resembled the proportions of a fat sausage—at some twenty feet in length and nearly seven feet across, quite a large sausage. See its picture on page 180, with a man and a Jeep to set the scale. (I once heard someone say that the name was adopted in part because cylinders of thermonuclear fuel could be joined end to end like sausage links. That etymology is questionable, since the term “sausage” was adopted immediately for a single cylinder and appeared in the title of the April 1951 report written by Freddie de Hoffmann and signed by Teller.{10} Still, one must note that in both de Hoffmann’s home city of Vienna and Teller’s home city of Budapest, linked sausages offered by street vendors were common sights.)
As to other details, they are, technically, still secret. However, among the many unclassified published accounts, there is a broad agreement about the design of Mike. I report that consensus view here. At one end of the long cylindrical steel container is the fission bomb that will provide the radiation and get the thermonuclear process started. The fission bomb is the “match” that will light the rest. Working in from the outside of the steel cylinder, there is a layer of mostly low-density material such as polyethylene, which provides an easy channel for the radiation. (In his first design, Garwin proposed liquid hydrogen in this space, because he knew better how to calculate its behavior when flooded with radiation.{11}) Then comes a cylinder of ordinary, non-enriched uranium—reportedly five tons of it. Within that is a huge stainless-steel “thermos bottle” (a dewar) containing the liquid deuterium that is the thermonuclear fuel. That “bottle” includes evacuated layers to inhibit heat flow from the deuterium, which is at a temperature of just 24 degrees above absolute zero (about–249 degrees Celsius). There is also cryogenic “plumbing” to maintain that low temperature.[77] And finally, running along the axis is a slender cylinder of plutonium 239 (the highly fissionable isotope)—subcritical, of course until compressed. Within it, according to some reports, is yet a final detail—a pencil-thin space at the center containing a very small quantity of a deuterium-tritium mixture, just enough to “boost” the plutonium fission by providing additional neutrons from the DD and DT reactions. This axial plutonium is called the sparkplug.{12}, [78]
What then happens when the fission bomb “match” explodes? Its radiation runs out ahead of its expanding material and almost instantaneously vaporizes the polyethylene, creating a very hot plasma. The pressure of this plasma adds to the pressure of the radiation, pushing outward on the outer steel cylinder and at the same time inward on the uranium cylinder, thereby keeping the channel open long enough to let more radiation stream in. At the same time, the outer layers of the inner cylinder “ablate” (boil off), creating even more inward pressure. Before long—within microseconds—an inwardly imploding shock wave has compressed and heated the cylindrical container of deuterium and also, through compression, caused the plutonium sparkplug to go critical. The sparkplug, which is really another fission bomb, helps to ignite and then enhance the deuterium burning—hence the name “sparkplug.” Finally, energetic neutrons emitted in the thermonuclear burning (especially those of 14 MeV from the DT reaction) cause fission in the ordinary uranium that surrounds the deuterium as well as more fission in the sparkplug. Altogether quite a maelstrom. So this “H bomb” is really one part fusion and three parts fission. Its total energy release (its “yield”) is estimated, in fact, to have come about three-quarters from fission and one-quarter from fusion.{13}
75
In the previous summer, when Garwin and I overlapped in Los Alamos, he had paid me a compliment by being surprised that I was still a student.
76
The last meeting of the Family Committee for which minutes are preserved took place in June 1951. The first official meeting of the Theoretical Megaton Group took place in late September or early October 1951.{8}
77
When working at Los Alamos, I turned down every invitation to see an actual bomb or mockup of a bomb. I didn’t want the wires and bolts and plates to intrude upon my visualization of perfect cylinders and perfect spheres. I thought that seeing the real thing might make me less effective as a designer.
78
Both of the two cited references in note 12 say that the central axial cavity in the spark plug contained tritium gas. Tritium alone would not have been helpful. It must have been a DT mixture as in boosted weapons.