Enrico Fermi came up with the basic idea using the power of a fission bomb to ignite fusion reactions -- a thermonuclear or hydrogen bomb -- as early as 1941. He told it to Edward Teller, who, as is well known, ran with it. For the next decade, Teller would commit a significant amount of his time to the effort of trying to figure out how you could make such a thing actually work.
That it took Teller -- and everyone else at Los Alamos -- a full ten years to figure out how to solve the problem is a good indication that it was a very hard problem. At the very least, it required a familiarity with nuclear reactions at energy regimes which had never been achieved previously on Earth. It also required breaking out of several wrong ideas along the way whose wrongness was not obvious.
There has been a lot written about the developments that led to the Teller-Ulam, or Ulam-Teller (as many fashion it), design in the spring of 1951. I find it more than a little fascinating that this old Cold War priority dispute is still alive and well in some circles, and have myself written a talk (which I probably ought to push to publication) with musings on the subject.1
The most basic form of it is that Stanislaw Ulam, a Polish mathematician, had considered that you could put a fission bomb into a heavy "box," set it off, and use the explosive pressure and heat of the blast to compress a larger piece of fissile material to very high densities. This would result in a very, very powerful (and very "dirty" from a fallout perspective) fission weapon, probably in the megaton range if you did it cleverly enough. Ulam told this to Teller, who jumped on it. As Ulam famously wrote to John Von Neumann: "Edward is full of enthusiasm about these possibilities; this is perhaps an indication they will not work."
Teller realized that the X-rays of the exploding fission "primary" were much faster than explosive forces Ulam was relying on, and could be used to compress fusion fuel to very high densities well before the bulk of the fission bomb's heat reached it. Somewhere along the line he also put a fission "sparkplug" inside the fusion "secondary," adding additional compression of the fusion fuel. Ergo, the multi-megaton hydrogen bomb. (Wikipedia, as you can imagine, has a long article on this thing, should you find my technical description lacking in detail.)
There's much, much more to it than this thumbnail sketch.
The result of all this, though, was a report signed by Teller and Ulam titled "On Heterocatalytic Detonations I. Hydrodynamic Lenses and Radiation Mirrors," report # LAMS-1225, dated March 9, 1951. Quite a mouthful. We'll get to the "heterocatalytic" in a moment, but the "hydrodynamic lenses" are the initial Ulam compression scheme; the "radiation mirrors" is related to Teller's insights with regards to radiation implosion. Presumably.
I've seen this report cited about a million times as "the" report, so I was surprised to find that there was a copy floating around online. Before you get too excited (or before my government readers flip out) the report is heavily redacted. Only a few paragraphs remain unadulterated, but it's still pretty interesting.2
Some close-reading thoughts follow, as well as a probably explanation for why the "Ivy Mike" shot cab was called "the Sausage." (It's probably not the reason you'd think it was.)
It's a 20 page document, and there were 20 copies made. Four of those were sent to DC; 14 of them kept at Los Alamos; and one of them was given to J. Robert Oppenheimer directly. That last bit I found a little surprising; it's obviously there because of the role the General Advisory Committee was perceived to be playing in decisions about the "Super" bomb, but it's still a little jarring to see Oppenheimer -- and just Oppenheimer -- named personally. (One could imagine other people who Teller would want to see this, too.)
The introduction is appropriately to the point:
In this discussion the following general scheme is considered. By an explosion of one or several conventional auxiliary fission bombs, one hopes to establish conditions for the explosion of a "principal" bomb. The latter may be either a fission or thermonuclear assembly.
Again, remember that the context of this is Ulam's initial idea for very high efficiency fission bombs, not just hydrogen bombs. The rest explains that the goal here is very high compression of relatively large masses of material (fusion fuel).
They clarify the "heterocatalytic" term as well:
The arrangement might be called heterocatalytic, involving as it does a setting off of a reaction in one system by a reaction started in another material -- the "auxiliary" arrangement is located at a considerable distance (from the purely nuclear point of view), like 50 cm to 5 meters. This is in distinction to hitherto-considered autocatalytic schemes based essentially on self-implosions of a mixture of nuclear substances.
So they're using "heterocatalytic" as a foil to "autocatalytic." An autocatalytic reaction is one where the reaction is increased by the action of the reaction itself. A regular nuclear fission chain reaction is technically autocatalytic -- the more fission reactions you have in a given "generation" of the reaction, the more you will have in the next "generation" (until you are out of fuel, or the assembly blows itself apart, or neutron-absorbing elements interfere with the reaction).
By contrast, "heterocatalytic" means that one reaction is driving another: fission reactions are trying to set off fusion reactions. Importantly, these two "systems" are physically separate. During the Progressive case in 1979, this physical separation of the fission "primary" and the fusion "secondary" was considered one of the "big secrets" of the hydrogen bomb. It seems kind of quaint from a layman's point of view, but remember that most assumptions about how hydrogen bombs were designed usually focused on putting the fission bombs as close as possible to the fusion fuel, with the idea that this would conjure up the necessary heat and/or compression.
Anyway, after the section quoted above, we have several totally blanked out pages. No surprise, there. Then we have some rather technical discussion of sound velocities in various medium; presumably this involves Ulam's plan to use the shock wave of the fission bomb to compress the "secondary" system.
Then more blank pages. Interestingly, there are call-outs for four figures. I suspect these are graphs of some sort, and probably not bomb designs, based on a conversation I had with Richard Garwin awhile back. (Garwin, incidentally, also said that Teller probably authored the whole paper, given how it was written.)
Lastly, we get one more dribble of text at the end:
In fact, the essential parts of the design do not depend sensitively on complicated shapes and the necessary planning is, therefore, comparatively simple.
Well, that's good to know, I guess.
Separately, one interesting H-bomb tidbit I stumbled across awhile back but haven't seen written up anywhere: the Ivy Mike device name was nick-named "the Sausage." I had always thought this was probably because this was because of its rather phallic appearance. According to an interview with Ted Taylor we have on file here at AIP, this is apparently not the case:
[John Wheeler] was talking about lots of what I think he called sausages, hooked up to each other so that a primary and a secondary and a tertiary -- actually in effect an infinite number eventually -- by having the radiation funnel down something that first imploded something small, then something bigger, than the radiation flowed down this tube, and what would go would be 10 stages maybe. Not necessarily 1-2-3. Now I don't know when that was, except that what I remember was that it was very soon after Teller and Ulam told people [their idea].3
In other words, "the Sausage," isn't about how it looks, but how it links.
So what do we take away from this? One is the fact that this document is redacted to the point of almost being useless. The introduction is nice (compression is important!) and the clarification of what "heterocatalytic" means is helpful, but other than that, it doesn't tell you a whole lot by itself, without being contextualized through all sorts of other sources.
Still, it's interesting to see even snippets of the holiest-of-holies: the document that birthed the megaton age.
- The portraits were scanned from George Gamow, My World Line: An Informal Autobiography (New York: Viking Press, 1970), on 153. [↩]
- Citation: Edward Teller and Stanislaw Ulam, "On Heterocatalytic Detonations I. Hydrodynamic Lenses and Radiation Mirrors (LAMS-1225)," (9 March 1951), Los Alamos National Laboratory, retrieved from http://www.nuclearnonproliferation.org/LAMS1225.pdf. [↩]
- Oral history interview of Theodore B. Taylor by Kenneth Ford, (13 February 1995), in the AIP Niels Bohr Library and Archives. Note that in the online transcription of this particular quote, it isn't clear who is speaking, but from the content it looks like Taylor to me, even though it is labeled as Ford. [↩]