Piece of the Sun : The Quest for Fusion Energy (9781468310412) Read online

  Soviet military strategists had a policy of developing the most powerful H-bombs that they could because they were lagging behind the US in the development of intercontinental ballistic missiles. Russia’s first strike capability relied on long-range bombers which were inaccurate and vulnerable to getting shot down. So there was a logic to building big bombs to give the few bombers that got through as big an impact as possible, and if they missed the city centre they were aiming for by a few miles the city would still be devastated.

  Even with that motivation, Tsar Bomba was not a practical weapon and was probably tested more as a show of strength to Russia’s adversaries. The device was 8 metres long and 2 metres in diameter, larger than the ‘Sausage’ exploded on Elugelab, and weighed 27 tonnes. It was so large that a TU-95V bomber had to be specially modified to carry it. The design – a Teller-Ulam type – could in theory create a blast of 100 megatonnes (Mt) by surrounding the fusion fuel with a tamper made of uranium-238 so that neutrons from the fusion explosion trigger another fission explosion in the tamper. But in an effort to reduce the amount of radioactive fallout, the test replaced the uranium-238 with lead and this reduced the blast to 50 Mt – still ten times the total amount of conventional explosives used in World War II.

  At around 11.30 on 30th October the TU-95V dropped the bomb above the island of Novaya Zemlya in the Arctic Sea. The bomb’s fall was slowed by a parachute to give the bomber and its escort time to get a safe distance of forty-five kilometres away but still the shockwave caused the planes to drop in altitude by a kilometre. The fireball could be seen 1,000 kilometres away and the mushroom cloud rose to seven times the height of Everest. A village fifty-five kilometres away was completely destroyed and there was substantial damage in towns hundreds of kilometres away; windows were broken in Norway and Finland, more than 1,000 kilometres distant; and the seismic shock caused by the blast was still detectable after it had travelled around the world three times. Tsar Bomba was the most powerful device of any kind ever built. To produce such a blast with conventional explosives would require a cube of TNT 312 metres on each side, roughly the height of the Eiffel Tower.

  At Livermore the explosion of Tsar Bomba was like a call of Action Stations! The US had to respond. After the brief pause of the previous few years everyone started preparing for new tests and Nuckolls had no time to devote to fusion engines. US testing resumed in April 1962 and there followed a furious six months of detonations by both sides. But the renaissance of testing was short-lived. Treaty negotiations resumed the following year and on 5th August the US, UK and the Soviet Union signed the Limited Test Ban Treaty which banned testing in the atmosphere, underwater or in space – so testing went underground. Nuckolls was kept busy designing nuclear weapons for the next few years, but not everyone at Livermore was directly involved in those efforts.

  Ray Kidder, whom Nuckolls had worked with in the non-nuclear primary group, was keeping a close eye on the development of lasers, first by Maiman and others at Hughes, and then elsewhere. Hughes researchers devised a technique for producing ultra-short laser pulses and then others at the American Optical Company found that you could make lasers by mixing various so-called rare earth metals, such as neodymium, in glass. This was much cheaper than the ruby used by Maiman and opened the possibility of large rods and discs of laser glass.

  Kidder carried out some rough calculations in late 1961 which suggested that a laser pulse with an energy of 100,000 joules (100 kJ) and lasting 10 nanoseconds might be enough to compress and ignite a small quantity of D-T fuel. The following April he visited Maiman at Hughes to discuss whether it was theoretically possible to scale up laser energy to hundreds of kilojoules. Reassured that there were no known obstacles, Kidder reported his results to Foster and soon he was heading the Livermore physics department’s new Q Division, devoted to the interactions of electromagnetic radiation with matter.

  Kidder and his colleagues began immersing themselves in the world of laser research and, in true Livermore style, Kidder devised a new simulation code optimised for laser-driven implosions. Using the new code in the summer of 1964, Kidder calculated that a laser pulse of at least 500 kJ lasting for 4 nanoseconds would be needed for ignition. After further refinement the estimate went up in 1966 to 3 million joules (MJ) in 5 nanoseconds. The estimated energy of the laser pulse required had gone up thirty times since Kidder’s first calculation in 1962 and the pulse length had halved.

  Most of the 1960s was spent learning about lasers and how their beams interact with matter at high energies. The key technologies developed during this period include methods of producing ultra-short pulses, with names like mode locking and Q-switching, and laser amplification. Researchers realised that after you had produced a beam using a laser you could shine the beam through some more lasing material, already pumped with energy but without mirrors at the end, so the beam gathers more light and energy as it passes through. In theory, a beam could be passed through dozens of these laser amplifiers to pump its energy up to a high level.

  Kidder’s team examined various laser materials to find which would be suitable for fusion and narrowed it down to two: iodine gas and neodymium glass. In the end they opted for neodymium glass (Nd:glass) because it was easier to work with. Neodymium ions made an ideal laser material. They could be pumped up with energy using relatively cheap xenon flashlamps and would stay in that state for 100 nanoseconds; plenty of time to form or amplify a laser pulse. Incorporating the neodymium into glass did cause some problems: often the refractive index of the glass – its ability to bend light – would vary which reduced the beam quality. So laser designers sought to use as little glass as possible in their designs. They would use sheets of Nd:glass 2.5 centimetres thick and shine light through it via the broad face. An amplifier was built up by arranging, say, sixteen disc-shaped sheets arranged in a row, each angled to the oncoming beam to prevent reflections. The sheets, since they were angled, could be pumped by flashlamps at the side.

  By the 1970s they were able to take a seed pulse from an Nd:crystal laser, with an energy of 0.001 J, and pass it through a series of amplifiers with a combined glass thickness of 1 to 2 metres to produce a pulse with an energy measured in kilojoules – an increase in energy of more than a million times.

  Also during the 1960s, it became obvious that the Livermore lab wasn’t the only game in town. Its sister laboratory at Los Alamos was also investigating lasers for fusion, including ones using gases such as carbon dioxide and krypton fluoride as the laser material. Researchers there also looked into the possibility of using laser-ignited fusion capsules as a propulsion system for rockets. Researchers at the Naval Research Laboratory (NRL) in Washington, DC also began a research programme into lasers to see what military applications they might have. They and everyone else in the laser community were surprised by news in 1966 that researchers in France had produced a 500 J pulse with lasers and amplifiers of Nd:glass. The best in the US at that time was less than 10 J. In 1967 NRL bought 60 J rod-shaped amplifiers from the French lab to study them and bought 500 J amplifiers in 1971. In 1967 Alan Kolb, head of plasma physics at NRL, heard a briefing in Washington about laser fusion by Kidder. Believing that NRL had superior skills with lasers than the two weapons labs, the naval researchers began their own programme of fusion research.

  Then came news from Russia that Nikolay Basov, one of the co-inventors of the maser, and some colleagues had used an Nd:glass laser to heat a sample of lithium deuteride and had detected neutrons. Although it wasn’t many neutrons, this was a sure sign that ions were undergoing fusion. Basov’s report didn’t suggest that the target was being compressed by the laser, only that it was being heated, so the team at Livermore were not too concerned that the Russians were ahead in what was rapidly becoming a race for laser fusion. What worried the Livermore researchers more was some documents circulating around the lab: they were patent applications from a commercial company claiming the invention of laser fusion through the radiation implosion of
small fuel capsules. The US Patent Office had sent the applications to Livermore for review. If they were granted then this company, KMS Industries, would control this new technology, not the government labs that felt it was their private reserve.

  The author of the patents was Keith Brueckner, a professor of physics at the University of California, San Diego. Brueckner had a finger in very many pies: he had done consulting work for the Los Alamos weapons lab, the Department of Defense and the Atomic Energy Commission. He had studied lasers and in the late 1960s was an adviser to the AEC on controlled fusion, having studied magnetically confined fusion at Los Alamos a decade earlier. In 1968 the AEC asked Brueckner to attend the International Atomic Energy Agency fusion conference in Novosibirsk as their representative. This was the meeting at which Lev Artsimovich sparked the race for tokamaks by revealing his results from the T-3. But Brueckner wasn’t there to find out about tokamaks; he was sent to find out what other countries were doing in laser fusion. He listened to reports from Russian, French and Italian researchers and mixed with them socially afterwards. Returning home, Brueckner wrote up a report for the AEC on what he had learned in Novosibirsk. He had become intrigued by the topic and talked informally with various AEC officials to see if the commission would fund him to carry out a more thorough investigation. He received no encouragement, presumably because, although Brueckner didn’t know it, the AEC already supported all the work in this area at Livermore and Los Alamos.

  Undaunted, Brueckner applied to the Department of Defense and was given a small (classified) research contract to investigate laser fusion. He started to study the idea of focusing the beams from a number of powerful lasers onto a small sphere of mixed deuterium and tritium and heating it enough to start fusion reactions. Normally, the heated plasma would rapidly expand but, because of its inertia, it would take a moment to do so. Like similar schemes, he was relying on that moment of inertia to be long enough for the plasma to reach fusion temperature. So the heating has to be very fast, requiring an ultra-short, powerful laser pulse. Because of this reliance on inertia, laser fusion is often called inertial confinement fusion.

  Not knowing about Nuckolls’ detailed simulations, Brueckner had only found rough calculations of the sort of pulse needed to achieve fusion. So, helped by some other theorists at UC San Diego, he developed simulation codes, taking account of the energy deposited by the laser beams, the conduction of heat in the plasma and its expansion, shock waves and the effect of any fusion reactions that occurred. In 1969 the code was finished and they started running some simulations. To their amazement the codes predicted that they would produce huge numbers of neutrons, hundreds or more times as many as they had expected based on estimates from other people’s work.

  They analysed in detail the output of the simulation and realised what had happened: rather than just heating the plasma the laser pulses where compressing the capsule and heating it too. Almost by accident they had stumbled on the idea of using a radiation implosion to trigger fusion. Brueckner’s calculations showed that it was possible to get much more energy out of a capsule using implosions and that they could achieve ignition with a laser pulse of only a few kilojoules, not much more than state-of-the-art lasers could produce at the time.

  It was around this time that Keeve ‘Kip’ M. Siegel, head of KMS Industries, became involved. In addition to all his government consulting work, Brueckner had, for the previous few years, been consulting for KMS Industries and when his meagre DoD funding for laser fusion proved inadequate Siegel’s company had provided some additional cash. Brueckner told Siegel about his simulation results. The industrialist was hugely enthusiastic and determined that this was something that KMS Industries had to be involved in.

  Kip Siegel was the quintessential American scientist-entrepreneur. Trained as a physicist, he became a professor of electrical engineering at the University of Michigan at Ann Arbor. Much of his work there was concerned with identifying aircraft and missiles using radar. He patented some of his inventions in the fields of radar and electro-optics and in 1960 set up a company, Conductron, to market them. Over six years he turned the company into one of the area’s biggest industries before finally selling it to McDonnell-Douglas for $4 million. Soon after he formed KMS Industries and built it up into a nationwide conglomerate by buying up other small high-tech companies.

  In spring 1969 Brueckner and Siegel went to visit Paul McDaniel, head of research at the Atomic Energy Commission in Washington. Because some of the work had been supported by KMS Industries, they asked McDaniel if he would treat the information they were about to give him as proprietary secrets. He said that if that was the case they should go away again and apply for patents before talking to anyone at the AEC. So they returned to California. Brueckner wrote up his results and applied for his first patent in the summer.

  Later in the summer Brueckner was in West Palm Beach in Florida for a meeting when he had a visit from the AEC’s head of security who told him that the work he was doing on laser fusion was related to classified weapons design work and that he was forbidden to do any more experiments or simulations, talk to anyone about his work, or even to do any calculations on paper. Brueckner soon learned that the Patent Office had, as a matter of routine, sent his patent applications out for comment to experts in the field, in this case to Livermore, Los Alamos and the AEC. Their contents had caused uproar, hence the crackdown by the AEC on any further work.

  The AEC’s reaction only served to convince Siegel even more that they were onto something important. Siegel got his lawyers to work on the AEC and eventually a compromise was struck whereby Brueckner alone could continue to work on laser fusion. During that autumn and into spring 1970, Brueckner continued his theoretical work and wrote up more patent applications, eventually producing a total of twenty-four. He was so annoyed by the AEC’s draconian restrictions that he made as many and as wide patent claims as he could. Meanwhile, Siegel’s Washington lawyers continued to lobby the AEC until finally in the spring it allowed KMS Industries to continue work on laser fusion. However, the research remained classified and under government control, KMS Industries would receive no funding, get no access to AEC research and could not hire former AEC employees.

  Siegel thought the work could be done with KMS Industries’ own resources and help from other industrial partners. While Brueckner and his colleagues at San Diego continued doing theoretical work, Siegel made plans and in spring 1971 announced that they would build a laboratory in Ann Arbor, raising money by selling off some divisions of KMS Industries. To entice Brueckner, Siegel offered him a significant fraction of any profits that came from the work, so Brueckner took leave from UC San Diego and moved to Michigan.

  The race for laser fusion was rapidly heating up. Evidence was emerging that Basov and his colleagues at the Lebedev Physical Institute had also discovered the importance of imploding the fusion target and a university-based effort in the United States was also joining the fray. This was the brainchild of Moshe Lubin, an Israeli researcher who came to the US in the early 1960s to study aeronautical engineering at Cornell University. In 1964 he joined the department of mechanical and aerospace sciences at the University of Rochester in New York State. Lubin was fascinated by the rapidly developing science of lasers, particularly the possibility of focusing beams down to produce high energy densities and the effect this might have on matter. His department at Rochester was fertile ground because there were already others there interested in plasma physics and the university had an Institute of Optics. Rochester is also the home of the Eastman-Kodak camera company which provided hardware for their laser development and studies of laser-matter interactions.

  By 1970 Lubin and his colleagues believed that lasers could heat a plasma sufficiently to ignite fusion reactions and in the autumn the university set up the Laboratory for Laser Energetics (LLE) with Lubin as its director. Lubin set out his manifesto in a 1971 article in Scientific American, describing heating fusion targets with Nd:glass
lasers. He predicted energy break-even with a laser pulse of less than 1 MJ and even described a reactor vessel with thick liquid-lithium walls to absorb the neutrons. That year LLE began work on Delta, a 1-kJ laser with four separate beamlines designed to carry out fusion experiments.

  The researchers at Livermore knew they had to respond to all this competition but were hindered by the slow-moving bureaucracy of the lab and the AEC. Nuckolls now had more time away from weapons design work and was again getting involved in fusion target design, teaming up with a young protégé of Teller’s called Lowell Wood. They lobbied hard in the lab and at the AEC for aggressive laser-fusion development, working towards a 10-kJ laser. Reports from Russia said researchers there had already achieved implosions using lasers with multiple beams while the teams at Rochester and the newly established KMS Fusion were already building similar lasers. While the researchers at Livermore had done huge amounts of simulation and investigated the properties of various laser systems, they had yet to fire a pulse at a fusion target.

  Nuckolls and Wood favoured building an Nd:glass laser which produces infrared light with a wavelength of one millionth of a metre (1 micron). Some pushed for the carbon dioxide gas lasers with a 10-micron wavelength being developed at Los Alamos. Although these were much more energy efficient than Nd:glass, it was believed that the shorter wavelength was absorbed more readily by the target and was less likely to be affected by plasma blasted off the target during the drive pulse. Others, including Kidder and Teller, thought that not enough was yet known about high-power lasers and so the research should progress more slowly, but the lab managers saw that lasers had wider uses in weapons physics and other military and industrial applications, so they backed the programme. The support of the AEC was won in early 1973 and laser building began.