Review of Kenneth Ford's book Building the H Bomb, a Personal History, with factually defensible suggestions for improving the nuclear deterrent mechanism
Ford's book is more concerned with opinions about various "personalities" like Edward Teller and Stanislaw Ulam than with event history or even physics; there are no equations, and no realistic discussion of nuclear nuclear weapons effects in modern cities, or specific effects enhancements like EMP or neutron output, and no discussion of credible tactical nuclear weapons for deterrence of invasions and conventional war to prevent general nuclear war by escalation: all the world wars of history began not by city bombing, but by invasions and military attacks on other countries/ships/naval bases (Belgium '14, Poland '39, the Lusitania '15 and Pearl Harbor '41).
Stanislaw Ulam comes across as being as arrogant as Teller. Ulam suggested in early 1951 making fission bombs of unlimited yield but getting a large metal case (like the Jumbo of 1945) and putting a complete fission weapon it it, together with separate subcritical bomb cores. The detonation of the former would release radiations that Ulam hoped would compress the additional subcritical fissile cores to an immense extent, thus making possible a purely fission weapon of unlimited power to replace the H bomb project.
Teller then seized Ulam's idea and added some fusion material around Ulam's additional subcritical fissile material to achieve a practical H bomb. Ford misses out, as do all other histories, the interesting fact that in a declassified 1950 H bomb committee ("Family Committee") meeting, Teller made the point that his whole basis for making a H bomb was by using magnetic fields to keep the fusion stage compressed, while being heated by X-rays from the primary stage.
This process led, even after the Teller-Ulam success, to intense work - that nobody mentions - by Ernest Lawrence and Teller's Lawrence Livermore laboratory on magnetic flux compression current pulses (simply a charged inductor coil wrapped around an expanding conventional or nuclear fission explosion stage, so that the explosion couples a fraction of its energy into the coil by shorting it out) to power electromagnetic compression of fusion fuel capsules (simply a coil of wire around the fusion capsule, which exerts a magnetic field when a current is injected into it. The magnetic field exerts pressure against electrically conductive ions, thus it compresses the hot, ionized fusion stage which excludes magnetic fields). Both magnetic flux compression and brief magnetic compression of laser-ionized fusion capsules have been successfully tested and published (X-ray ionization by fission explosions is also feasible in place of laser heating used in fusion power experiments). Simply plugging the output current pulse cable from the magnetic flux compression generator into the electromagnetic used to compress the fusion stage, couples them together, allowing an alternative/supplement to X-ray coupling:
Above: the earliest declassified mention of the possibility for using magnetic fields to compress the ionized fusion charge, to boost the efficiency of the burn process in the H bomb. But the story of the magnetic flux compression (current pulse generator) and the use of current-pulse driven electromagnets to compress fusion plasmas does not end in 1951, with the rival X-ray coupling method. Teller's Lawrence Livermore National Lab expert on fission weapons, John S. Foster, Jr., developed and patented the use of magnetic flux compression generators (see for example, slide 18 here) using conventional explosions. Today, the output of these are usually coupled to a horn antenna to produce non-nuclear EMP. To give a specific example, see his U.S. Patent 4,370,576, Electric generator (magnetic flux compression), filed in 1962 but kept secret and only published in 1983, complete with a graph plotting the immense 10^7 amps (10 mega amps) current generated within 200 microseconds!
The original motivation was to use the rapidly increasing ionization in a nuclear fission explosion to produce displace (or short) the magnetic field of a charged inductor coil around it, into which a massive current would be induced (the ionization rise time is far smaller in a conventional explosive). The thick conductors would transmit that powerful current pulse into a physically separate electromagnet coil surrounding the fusion stage of the thermonuclear weapon, which would be compressed by magnetic fields after being ionised by nuclear radiations and X-rays from the primary stage. Simultaneously, Teller and others pushed for research into the magnetic compression of plasmas in "controlled nuclear fusion", which was inevitably hyped and sold as a peaceful alternative to the H bomb. Yet this remains an important idea for cleaner, mini H-bombs, for reasons we'll explain in detail below.
Although widely eclipsed by Teller's later idea to use recoil from X-ray ablation of a dense metal pusher, magnetic compression for thermonuclear weapons was discussed in detail at Edward Teller's Family Committee, 27th meeting, 15 November 1950, LAMD-470. Teller's Family Committee was appointed to investigate the H bomb after President Truman's authorization following the first Russian nuclear test in 1949, despite American secrecy. The Family Committee's last meeting was in June 1951 after the X-ray ablation idea of Teller, following indirect stimulation from Ulam. The Family Committee was replaced by the "Theoretical Megaton Group" in September 1951. A basic sketch for the idea of magnetic coupling is shown in Figure 1, below, where the ionization of the materials of a hot fission stage weapon couples energy into a charged inductor coil surrounding it by pushing out the magnetic field (which can't penetrate electrically conductive, ionized media). This can couple a vast amount of electrical energy as current into that inductor coil, which is cabled to another coil around the fusion stage, which acts as an electromagnetic, squeezing that stage when it has ionized. Then X-rays are thus used only for heating the fusion fuel, magnetic fields for squeezing it:
Figure 1: magnetic coupling method. For cleaner nuclear weapons using low yield kiloton fission primary stages, we need to move away from traditional X-ray coupling and embrace proof-tested cable coupling. We pick up energy from the fission primary stage explosion when it ionizes and excludes magnetic fields, thus shorting out the magnetic field of the pre-charged inductor coil wound around it (left of diagram). This shorting couples energy from the primary stage into the coil, which can be cabled as a current pulse into a secondary coil wound around the fusion stage, which exerts a magnetic field that compresses it when it is ionized, enhancing the X-ray heating effects.
This is just a sketch of Teller's concept: the two systems have been tested using conventional explosives and pulsed fusion reactors with magnetic compression. (We omit charging circuit that primes the inductor coil, as well as omitting switches in cable to the electromagnet around the secondary stage.) Objections like ablation of the wires are superfluous because of the timing and simple safeguards like wrapping cables in plastic insulators which take time to ablate, or simply using thicker cables where needed as indicated by computer simulations to prevent such failures. As always, the complex details involve timing issues, like ensuring the magnetic compression pulse arrives at an optimal time after the X-rays and neutrons hit the lithium deuteride, This is a matter for fine-tuning in computer simulations and experiments. The Holy Grail is a cleaner low yield nuclear deterrent to prevent the aggressive attacks and invasions that triggered world wars (they did not start with city bombing, which was the result of escalation after wars began).
Teller's magnetic compression idea is unnecessary for very high yield H bombs, where a relatively large yield (say 100 kt or so) fission primary stage is used, which emits a significant proportion of its energy in X-rays. But if using a fission primary stage or 1 kt or less, which is important in tactical and cleaner nuclear weapons, little of the energy is released as X-rays because, as Brode explains in his 1968 Annual Review of Nuclear Science paper, "Review of nuclear weapons effects, the energy is partitioned between kinetic energy of particles (energy proportional to temperature) and X-ray radiation (energy proportional to temperature raised to the fourth power). The two terms force most of initial energy of a nuclear explosion into X-rays if the fission stage yield is substantially over about 10 kilotons, but most of it is in massive particles (not radiation) if the yield is below about 1 kiloton.
Hence, to get efficient ignition of a cleaner fusion explosion for low yields of fission primary stages, you need Teller's 1950 magnetic compression idea. (This is not used in today's relatively high-fission, dirty nuclear weapons, and an expensive quick fix rather than Teller's idea was used in the W79 neutron bomb, replacing lithium deuteride with an expensive D+T gas fusion capsule, to maximise the fusion energy yield.) If cable coupling and magnetic compression of the fusion stage were used, we could compress the fusion stage for long enough for neutrons from the primary stage to fission lithium, producing tritium from lithium deuteride without requiring a spark plug, and thus arriving the Holy Grail of nuclear weapons, a low yield, cleaner long-shelf life (i.e., no gaseous tritium) deterrent to the invasions and military aggressions that cause terrible wars. Unfortunately the nasty, "it's taboo" attitude problem from nearly everybody against improvements will mean that we will be the last folk to get this vital technology. Even the North Koreans are testing, but we're not!
The tremendous nuclear weapons deterrent significance of being able to magnetic coupling for fusion compression in place of X-ray coupling is that we can use a very low fission yield to set of any yield of fusion we like by using the entire encased mini H bomb as a primary stage in a Russian doll design, for example:
Or for very high yield almost entirely "clean", nuclear weapon deterrents for aircraft delivery, something like:
Going back to Ford's book, he quotes Teller debunking Stanislaw Ulam, as follows:
"Years later, Edward [Teller] said to me (I paraphrase), 'Stan had a dozen ideas a day. They were almost all crazy. He himself had no idea which ones were valuable. It took me to pick out of the jumble the one good idea and exploit it"."
Ironically, this sentence from Teller is similar to Brode's view on Teller's nuclear weapons design ideas output which we quoted a few posts ago! It is also very similar to the view Koestler has (in The Sleepwalkers) of Newton's "genius" residing in his ability to pick out useful laws from the immense clutter of speculative ramblings and pseudoscience ideas in Kepler's long-winded rambling books (which others apparently found boring, throwing out the babies with the bathwater), and also closely reminiscent of the view one military adviser (see Alanbrooke's memoirs) gave of Winston Churchill's immense daily output of good and bad ideas in WWII.
Ford does add a couple of additional references. First, he cites Edward Teller's 4 April 1951 Los Alamos report LA-1230 with Teller's conceptual idea for the Mike test, titled The Sausage - A New Thermonuclear System. Secondly, he cites the Los Alamos report by Richard Garwin that began the process of translating Teller's LA-1230 ideas into an engineering blueprint, LAMD-746, Some Preliminary Indications of the Shape and Construction of a Sausage, Based on Ideas prevailing in July 1951. (On page 155, Ford says that this report by Garwin "laid out a design with full specifics of size, shape, and composition, for what would be the Mike shot fired the next year.")
One problem in Ford's and other popular descriptions of the Teller-Ulam has always been the inclusion of plastic preventing X-rays from rapidly delivering a short pulse of ablation to the secondary stage's metal-surfaced pusher. Garwin was well aware that a very brief X-ray delivery time is of the essence, something that Sublette and others tend to ignore, despite the fact that force is the rate of change of momentum, F = dp/dt. This fundamental equation (Newton's second empirical law of motion) proves that the shorter the duration of delivery of energy to the surface of the metal surface of the fusion fuel stage, the greater the ablation recoil force that causes compression of the thermonuclear fuel capsule.
The majority of the energy released in a low yield fission weapon comes off in the last shake, a period of about 10 ns. If you have plastic foam filling the radiation channel, then since the mean free path of X-rays is small in plastic, it slows down and diffuses the energy delivery rate, massively reducing the force. So you have a much slower delivery of energy to the secondary stage, than you get using light speed X-rays in empty space (so you don't fill the radiation channel with plastic, but merely use a layer of plastic attached to the inner surface of the outer casing of the bomb, to act as a re-radiation "mirror" for X-rays). Instead of a brief duration of ablation (maximising the force of compression), if plastic foam fills the bomb, you then get a longer duration which reduces the force F = dp/dt. The time factor makes the pressure from plastic foam so slow-rising that the outer case of the bomb blows off allowing the fireball to expand and the pressure to fall before the secondary stage has been compressed. There's nothing secret or speculative here. It's very basic science. The fact is, unless just used a layer for X-ray mirroring purposes, plastic foam hinders a clean, brief delivery of X-ray energy to the dense metal ablation surface of the fusion fuel capsule. Instead, you get poor compression because of the the slower rate of delivery of energy.
The only times you would use plastic foam are in a layer confined to the inner surface of the outer radiation case (to minimise ablation of the outer case, and thus to maximise re-emission of X-rays instead or so-called "reflection", thus Teller's "radiation mirror" description of plastic foam) or if you deliberately wanted to delay and reduce efficient X-ray energy transfer (for example, if you didn't have any spark plug or fissile material in the secondary stage, and wanted time for neutrons from a primary stage to arrive at the fusion stage to split lithium, prior to compression of the secondary stage, maybe in a cable-coupled design of the type we illustrated above).
Confusion on this stems from Ulam's original idea to use hydrodynamic shock wave, for instance a shock wave of ionized plastic (not X-rays) from a primary fission bomb to compress a secondary fissile core. This is not the X-ray ablation mechanism. Garwin, Ford reports on page 156, originally proposed filling the radiation channel with ordinary hydrogen to act as a hydrodynamic lens of the Ulam sort. However, as Harold Agnew and others report in Rhodes' book Dark Sun, this was changed to plastic foam X-ray radiation mirror nailed into the lead lined outer case. The plastic foam was originally a cheaper, safer version of the older H-bomb idea (the 1946 poorly-compressed von Neumann-Fuch H bomb patent) of using beryllium oxide to compress fusion material, as Ford explains on page 100:
"Then comes the radiation and the ingenious part of the von Neumann-Fuchs invention. The flood of radiation from the fission bomb would completely ionize the BeO shell and its DT contents ... Since beryllium is the fourth element ... and oxygen is the eighth ... there are now 14 particles (4 electrons and 1 nucleus from the Be atom, 8 electrons and 1 nucleus from the O atom). Inside the capsule, however, 1 D atom and 1 T atom would together yield only 4 particles (2 each). So the BeO plasma, now having many more particles per unit volume than the DT plasma, would experience a much greater increase in pressure and would exert a mighty compressive force on the DT. Von Neumann and Fuch estimated that this 1:2 punch of a direct hit by the fission bomb followed by radiation induced implosion of the BeO capsule would result in a 10-fold compression ..."
The role of plastic foam as a X-ray radiation mirror is entirely different, but this quotation does show that there are other uses for low-atomic weight material (whether BeO or plastic foam) that may be used. On page 21, Ford quotes Teller's description of a 15 February 1951 meeting with Ulam:
Ford adds on page 22 that he interviewed Carson Mark at Los Alamos on 24 February 1995 and asked about the Teller-Ulam idea, and he didn't even remember Ulam mentioning the compression of fusion fuel at all, just using a fission explosion to compress additional plutonium more effectively; Carson Mark told him:
"... Stan Ulam came to my office. He announced that he had an idea: use a fission explosion to compress the deuterium ... Compression had been suggested by various people ... But this was the first time that I did not object ... Stan then proceeded to describe how an atomic explosion should compress several enclosures of deuterium through hydrodynamic shock. His statement excluded my realization of why compression was important, and it also included details that were impractical. I told him that I had thought of something that might work even matter: it would be much more effective to compress the deuterium with the help of [emphasis added] radiation ... But Stan was not interested in my proposal and refused to listen. Finally, to put an end to the discussion, I told him that I would write up both proposals [ Hydrodynamic Lenses and Radiation Mirrors, 9 March 1951, Los Alamos LAMS-1225 ], and we would sign it as a joint report."
"... Stan didn't know anything about what we were doing [fission weapons research], came in and dismissed the whole thing, and said that it'd be a lot more interesting to explore the effects you could achieve with a bomb in a box. Put a bomb there and wrap a heavy case around it. Energy will come out and down here in the corner we can put a very small amount of plutonium and compress it to a very high degree ... All very correct statements, not having any relation to the super at all ... He gave me this long lecture. Then the next day he went and spent an hour with Edward in Edward's office, and Edward immediately applied the ideas he was talking about to the effect they might have on a thermonuclear assembly."
So it appears from Carson Mark's account that Teller was over-crediting Ulam in claiming he was talking about thermonuclear weapons at all, and Ulam certainly didn't know or suggesting using X-ray ablation and plastic mirrors to "reflect" some of the X-rays back from the bomb casing on to the metal ablation surface of a fusion fuel capsule.
One last parting observation on the nuclear weapon design secrecy business: on pages 166-7, Ford observes that he accurately enough (for practical purposes) simulated the thermonuclear ignition in the first H-bomb in the summer of 1952 using the SEAC computer which has a mere 1 MHz clock speed and a mere 10 kB (10 kilobyte) memory. Today, most people have access to computers over a thousand times faster (>1 GHz) with over 100,000 times as much RAM (i.e. 1 GB or more). Millions of people can program equations. This blows the smoke out of the illusion that "secrecy makes you safe". Secrecy makes you complacent, preventing the defensive measures and funding necessary to combat real threats. The Cold War proof tested way to prevent escalating wars is to deter and stop invasions and military aggression until the enemies go bankrupt. Secrecy undermines the credibility of nuclear deterrence: there is no harm in Russia building anti-tank neutron bombs, or an arms race of that sort, because we're not planning to invade Russia. If both sides prevent invasions, you get peace, not war. The whole bigoted "anti-nuclear movement" is a danger because it is against the most vital improvements for deterrence and safety, like cleaner designs. It has no real interest in anything except delusion and factually debunked political idealism.
Further reading: http://www.sandia.gov/pulsedpower/newsreleases/reports/Pulsed_PWR_1st_40yrs.pdf