Sausage and Alarm Clock
About the late summer of 1950, Teller suggested that Li6D might be used instead of pure D in the "Alarm Clock." This showed up very well in theoretical calculations. When combined with the radiation implosion, it gives promise for a practical thermonuclear weapon. However, the theoretical probability of satisfactory working of the 'Alarm Clock" was far smaller because of the likely occurrence of Taylor instability. For the further development of thermonuclear weapons, tests of components rather than full-scale weapons appeared fruitful. One or more tests of Taylor instability were proposed in connection with the "Alarm Clock."
Beginning already in the Summer of 1951, results were obtained from machine calculations and were very encouraging. Results on the efficiency of radiation transport were obtained at Los Alamos in the Fall of 1951, and reasonably definitive calculations were made by the Matterhorn Project in Spring 1952. By combining these results, it probable that the combination of radiation implosion and thermonuclear reaction would work.
Stanislaw Ulam and Edward Teller's principle of radiation implosion broke a theoretical logjam and quickly led to the first workable model of a hydrogen bomb that could be tested. This approach was the one of which Robert Oppenheimer was later (1954) to say, "The program we had in 1949 was a tortured thing that you could well argue did not make a great deal of technical sense .... The program in 1951 was technically so sweet that you could not argue about that."
By mid-1952 there were two promising ways to obtain large-scale thermonuclear reactions, namely the "Sausage" and the lithiated "Alarm Clock." The "Alarm Clock" became practical only by the inclusion of Li6 (in 1950) and its combination with the radiation implosion.
Teller and Ulam's promising design, radiation implosion, was translated by Richard Garwin into a working design. The detailed thermonuclear design was furnished by John Wheeler and collaborators.
In March 1952 the first large-scale hydrodynamic calculation was completed in Los Alamos on the new computer, the MANIAC (mathematical and numerical integrator and computer). At this time, unforeseen difficulties appeared. These difficulties could only be minimized by a very major redesign. Neutron preinitiation, which would have caused the Mike device to fail, forced its eleventh-hour redesign. This redesign came at the latest moment compatible with meeting the test date of November 1952. Had Teller's earlier test date been accepted, redesign would have been impossible and the test would very probably have failed. The theoretical program had proceeded at maximum speed from the moment this device was conceived.
This rate of progress was only possible by the extensive use of high-speed computing machines which did not exist a year earlier. The calculations made in connection with the design of the Mike shot were essentially all made in the year between mid-1951 and mid-1952. With the computing resources available a couple of years before, it would have been impomible to comprees the same amount of work into anything like as short a period.
The "George" test as part of Operation Greenhouse on 9 May 1951 became the first thermonuclear proof of principle test. The test device, named the CYLINDER, consisted of an enriched uranium core which was imploded using a unique cylindrical implosion system. The test was originally planned to study the ignition concept for the "Classical Super" thermonuclear weapon design, which by that time was known to be infeasible). The test fortuitously provided useful data on radiation implosion, an essential element of the Teller-Ulam design which had been devised just two months prior.
The design of the triggering system in the "George" test was based on the one patented by Fuchs and von Neumann in 1946. The device -- a disk about 8 ft across and 2 feet thick -- was perforated by an axial hole which was compressed to a narrow channel by the implosion. This channel conducted thermal radiation to a small beryllium oxide chamber containing several grams of cryogenic deuterim-tritium mixture. The thermal radiation heated the fuel chamber to fusion temperatures, and the pressure in the BeO wall caused it to implode and compress the fusion fuel. The thermal radiation arrived ahead of the shock front of the fission explosion, allowing time for the reaction to occur before being engulfed by the expanding fission fireball.
The "Item" test on 25 May 1951 was the first test of the principle of fusion boosting. The thermonuclear fusion reaction injected neutrons into the fission core to boost efficiency. The Item device used a cryogenic deuterium-tritium mixture inside an enriched uranium core. The boosting approximately doubled the yield over its expected unboosted value.
As Hans Bethe recalled many years later, "The theoretical design of Mike was completed by June 1952 in good time to make the device ready for testing on November 1." On 31 October 1952 the first hydrogen bomb -- the Sausage device detonated in the Ivy Mike test -- was successfully exploded. Designed by Richard Garwin, the first hydrogen bomb, employed a fission bomb (the primary) to compress and ignite a liquid deuterium secondary. Three stories tall and weighing over a million pounds, Mike was a bomb only in the explosive since. It was not a deliverable weapon.
The early liquid-fueled design was impractical, due its massive size which made it undeliverable. It was also economicly unfeasibility due to its insatiable appetite for scare and expensive tritium, which could only be produced at the expense of plutonium for the fission weapon stockpile.
From 1951 until 1956, hydrogen bomb research focused on using dry fuel. This change reduced the size of thermonuclear bombs and made them deliverable by aircraft, including the Navy's smaller, carrier-based planes.
In the course of running the Super Problem at Princeton in 1953, which involved about three or four months of effective computing time for eight hours a day, the number of basic arithmetic operations (multiplications, additiona, and so forth) performed was of the same order of magnitude as the total number of such operatiom performed at Los Alamos (excluding the arithmetic done on the Los Alamos MANIAC) from its beginning in 1843 up to that time.
In 1954 Los Alamos Laboratory successfully demonstrated the feasibility of dry, solid thermonuclear fuel for thermonuclear weapons. This development greatly simplified the weaponization and engineering of all subsequent generations of thermonuclear weapons. The first thermonuclear bomb containing solid fusion fuel was the Castle-Bravo shot.
The Shrimp device tested in Bravo on 28 February 1954 was the first "dry" or solid fuel (lithium deuteride fueled) H-Bomb tested by the US. It was also the largest bomb ever tested by the US, dramatically exceeded predictions (6 Mt predicted, estimated actual yield 15 Mt). The fuel consisted of 37-40% enriched lithium-6 deuteride encased in a natural uranium tamper. The unexpectedly high yield was due to the "tritium bonus" provided by the lithium-7 isotope which made up most of the lithium. This isotope had a substantial reaction cross section with the high energy neutrons produced by tritium-deuterium fusion. When these high energy neutrons collided with a lithium-7 atom, it could fragement it into a tritium and a helium atom. Tritium was both highly reactive and caused extremely energetic fusion, so this extra source of tritium greatly increased the weapon yield.
Previously, dry weapons were regarded as economically unfeasibly, based on the mistaken assumption that only the Li-6 isotope could be used efficiently as fuel. This belief was dispelled by this first detonation of a solid-fueled thermonuclear device. This showed that even ordinary lithium, unenriched beyond 6.5% in the Li-6 isotope, was useful as a thermonuclear fuel. As a result, many new and expensive lithium isotope-separation plants would not be required beyond those already planned.
Koon [6 April 1954] was the first thermonuclear device to be designed by Lawrence Livermore, and the last weapon design on which Edward Teller directly worked. It was a fizzle - with a predicted yield of 1 megaton its actual yield was only 110 kt. Of this, 100 kt was from fission (almost entirely due to the primary), only 10 kt of energy was contributed by fusion reactions. The test device was name Morgenstern ("morningstar"). Intended to break new ground in weapon design, it had a more complex internal design than the Los Alamos devices. There was an unexpectedly long time delay between the primary firing and the secondary ignition. A simple design flaw allowed the neutron flux from the primary to pre-heat the secondary, causing poor compression. Other devices tested in Castle contained boron-10, which served as a neutron shield to reduce this pre-heating effect.
The Zombie device tested in Nectar on 13 May 1954 was a prototype of the TX-15 lightweight thermonuclear weapon. This bomb was a transitional design between fission bombs and the classic conception of a hydrogen bomb. Zombie began as a radiation imploded fission bomb, similar to Ulam's original conception of using one fission bomb to compress another. The enriched uranium outer case of the secondary was retained, but the design evolved to include fusion fuel (lithium deuteride and tritium) to boost the yield. The result was a radiation imploded boosted fission bomb. The requirements for compression were relaxed compared to the other two stage thermonuclear systems tested in Castle. The other systems required efficent compression of low density fusion fuel to extremely high densities when the fission "spark plug" in the center ignited it. Zombie - by using a secondary case made of highly enriched uranium - would become supercritical through a much less demanding compression process. Zombie could be made smaller and lighter than the other thermonuclear systems tested in Castle.
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