Written by: Stephen Hsu
Primary Source: Information Processing, 7/27/2019.
Michel Carayol, father of the French H-Bomb.
The article below illuminates several mysteries concerning the French development of thermonuclear weapons. Why did it take so long? Did the French really need help from the British? Who had the crucial idea of radiation compression?
Without men such as these, how long would it have taken to develop breakthrough technologies that defined the modern age?
Nonproliferation Review 15:2 353, DOI 10.1080/10736700802117361
Based on the first-person account of coauthor Pierre Billaud, a prominent French participant, this article describes for the first time in such detail the history of the development of the French hydrogen bomb in the 1960s and the organization of military nuclear research in France. …
On November 1, 1952, the United States conducted its first thermonuclear test, ‘‘Ivy Mike,’’ seven years and three and a half months after its Trinity test. It took the Soviet Union four years (August 29, 1949 — August 12, 1953) and the United Kingdom four years and seven months (October 3, 1952 — May 15, 1957) to achieve thermonuclear capacity. And in the following decade, China did it, with its sixth test, in fewer than three years (October 16, 1964 — June 17, 1967). Yet after Gerboise Bleue it took France eight and a half years to reach the same landmark, detonating its first thermonuclear device on August 24, 1968. Why such a long delay, especially since the French were pioneers in nuclear research?
1965: What We Knew About the Technical Aspects
From 1955 to 1960, as we prepared for the first French atomic test, we were also pondering thermonuclear weapons. But the prospect of hydrogen weapons seemed so far into the future that we did not work seriously on it. … Li6D was commonly considered the best fuel for thermonuclear weapons, but we did not have any idea about how to burn it. All the problems with the thermonuclear bomb can be summarized by this question: how to discover the process that will allow the Li6D to undergo a fusion reaction?
… Compared to our American colleagues in 1948, French scientists had many advantages: we knew that hydrogen bombs existed and worked and that they used Li6D, and we understood the reactions at work. We also had powerful computers, of U.S. origin, which were not available in the late 1940s. And we knew, more or less, the dimensions and weights of the nuclear weapons deployed at NATO bases in Europe and their yields. …
De Gaulle: It’s taking forever! … I want the first experiment to take place before I leave! Do you hear me? It’s of capital importance. Of the five nuclear powers, are we going to be the only one which hasn’t made it to the thermonuclear level? Are we going to let the Chinese get ahead of us? If we do not succeed while I am still here, we shall never make it! My successors, from whatever side, will not dare to go against the protests of the Anglo-Saxons, the communists, the old spinsters and the Church. And we shall not open the gate. But if a first explosion happens, my successors will not dare to stop halfway into the development of these weapons.
… In January 1967, I published a voluminous report wherein I presented and developed my idea from late 1965, left idle since, explaining why the current studies were going in the wrong direction and producing a ridiculously low thermonuclear efficiency. I proposed a scheme with two consecutive steps: a cold Li6D compression increasing the density, from the normal value of 0.8 g/cm3, by a factor of at least 20, followed by a sufficient temperature increase (the ignition). In this report, I also gave orders of magnitude of the energies involved in each step… [[ One can make the (flawed) analogy of Billaud to Ulam (multi-stage insight, but no mechanism for compression), and Carayol to Teller (proposed the right mechanism for compression, although in Teller’s case he may have learned of it from von Neumann and Fuchs!!!). ]]
In early April 1967, Carayol had the idea that the x-rays emitted from the fission explosion could transport the fission energy to the thermonuclear fuel chamber to induce the necessary compression. He published a brief paper wherein he presented, and justified mathematically, his architectural idea. This was the key to the solution for an efficient thermonuclear explosive device, consistent with the current data about U.S. hydrogen weapons. Carayol had rediscovered the radiative coupling concept first introduced by Americans Stanislaw Ulam and Edward Teller in January 1951.
Michel Carayol, the Genuine Father of the French H-Bomb
Michel Carayol was born in 1934 and died in 2003. His father was an industrialist and his mother a teacher. He entered Ecole Polytechnique in 1954, graduated in 1956, and joined the Armament. In 1962, he was part of the DEFA assigned to CEA-DAM at Limeil. In 1967, Carayol was part of the advanced studies branch.
… Soon after, in April 1967, Carayol wrote a brief report describing his proposal for a cylindrico-spherical case in dense metal, containing a fission device on one side and a thermonuclear sphere on the other. The report showed that the photons radiated by the primary *still very hot* in the X-ray frequency range, swept into the chamber rapidly enough to surround completely the thermonuclear sphere before the metal case would be vaporized. Carayol had discovered independently a scheme equivalent to the concept developed by Ulam and Teller in the 50s.
But Carayol’s insight was ignored! It was British assistance that alerted project leadership to the value of Carayol’s ideas. It is not enough for some isolated genius to make a breakthrough — the people in charge have to understand its value.
… During the first months of 1967, Viard had told me, ‘‘A British physicist is showing some interest in what we do.’’ At several embassy parties, a first-rate British atomic scientist, Sir William Cook, former director during the 1950s of thermonuclear research at Aldermaston, the British center for atomic military applications, had approached the military attache´ at the French Embassy in London, Andre´ Thoulouze, an Air Force colonel, and had hinted to our nuclear research program. Thoulouze had previously been in charge of an air force base and knew Rene´ David, who would later work at the DAM. For this reason, instead of contacting the French main intelligence services, Thoulouze directly contacted our information bureau at CEA, the BRIS, where David was working at the time. In analyzing the fallout from the French tests, the Americans, the British, and the Soviets knew that we had not made any real progress on the thermonuclear path. In 1966 and 1967 we had tested some combination of fission with light elements. Cook told Thoulouze that we had to look for something simpler.
Two weeks after the Valduc seminar, on September 19, and while the work resulting from the Valduc decisions had not yet concretely gotten under way, Thoulouze came from London bearing information from this qualified source. Jacques Robert immediately convened a meeting, in the DAM’s headquarters in Paris, to debrief this information. Only three other people attended the meeting: Viard, Bonnet (DAM’s deputy), and Henri Coleau (head of the BRIS). The information, very brief and of a purely technical nature, did not consist of outlines or precise calculations. Nevertheless, it allowed Bonnet to declare immediately that the Carayol design, proposed unsuccessfully as early as April 1967, could be labeled as correct.23 Had this outline not already been in existence, we would have had a difficult time understanding the information and might have suspected an attempt to mislead us. In fact, this was a reciprocal validation: Carayol’s sketch authenticated the seriousness of the source, while the latter confirmed the value of Carayol’s ideas. Without realizing it, as very few were aware of Carayol’s discovery (and surely not Cook), he had given us a big tip and unexpected assistance, as this information also freed us from the ministerial harassment to which we had been constantly subjected. From that moment, things moved briskly.
Physicist Michel Carayol laid out what would be the fundamental idea of radiation implosion in an April 1967 paper, but neither he nor his colleagues were immediately convinced that it was the solution, and the search continued.
In late September 1967, Carayol’s ideas were validated by an unlikely source, William Cook, who had overseen the British thermonuclear program in the mid-1950s. Cook, no doubt at his government’s behest, verbally passed on the crucial information to the French embassy’s military attaché in London. Presumably, the British provided this information for political reasons. British Prime Minister Harold Wilson was lobbying for the entry of the United Kingdom into the Common Market (European Economic Community), which was being blocked by de Gaulle.
Note Added: Perhaps someone can translate part of this paper, which gives some details about the Chinese thermonuclear step, credit to Yu Min. Did they invent a mechanism different from Ulam-Teller? I can’t tell from this paper, but I suspect the initial Chinese design used U-T. There are claims that Yu Min later developed, in the pursuit of miniaturization and improved safety, a qualitatively different design.
Yu Min was a student of Peng Huanwu (also a key figure in the bomb effort), who was a student of Max Born. Yu Min only recently passed, in early 2019!