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

  The power had peaked for only around two seconds and reached a maximum value of 1.7 MW which amounts to Q=0.15, although this would have been Q=0.5 if a 50:50 D-T mixture had been used. JET was lauded in headlines and news bulletins around the world. Although the Culham researchers only performed two D-T shots, they had entered the era of burning plasma and they had done it before Princeton. But it would be a while before they would be able to do it again because JET was soon shut down to fit a divertor and the spotlight moved across the Atlantic.

  * * *

  JET’s success caused some gnashing of teeth in Princeton because researchers there felt they could have got their first. Bob Hunter, their boss at the Department of Energy at the time, wanted a better understanding of the plasma before moving on to D-T so they continued to perfect the art of performing supershots. They consoled themselves with the thought that 10% tritium wasn’t ‘proper’ fusion, and that they would be first to produce a fully burning plasma.

  Just as at Culham, there was an enormous amount of work to do to get ready. It was all hands on deck with large crews of physicists and engineers working to prepare TFTR, doing double shifts and working on Saturdays. Because the lab was close to the town of Princeton and they would be bringing radioactive tritium onto the site, lab director Harold Furth worked hard to reassure local residents. The scientists held open meetings, explained their plans and answered questions. Their tritium handling facilities were reviewed, and reviewed again. At one stage a ‘tiger team’ of as many as fifty people descended on the lab for a week to thoroughly inspect all their procedures.

  Finally the day arrived. Much thought had gone into how to publicise the event. Journalists from The New York Times and other publications were invited and some spent most of the week there. The lab employed its own film crew to record events and then to produce short items for TV stations to use. There were so many people there that most had to watch events on screens in the lab’s auditorium. Everyone was given identity badges with colours signifying their level of access – only those with the coveted red badge were allowed into the TFTR control room. After each preparatory shot was made, researchers would come to the auditorium to update the audience on what was happening. The team was deploying its full arsenal of neutral particle beams, with a total power of nearly 40 MW. The control room had an area called ‘beam alley’ where twelve people sat each tweaking one of the dozen beam sources to get maximum power out. Instead of a camera looking into the vessel, the TFTR team had positioned a sheet of material called a scintillator inside the neutron shielding next to the reactor and a camera was set up looking at the scintillator. When a neutron hit the scintillator it would produce a small flash of light so the amount of flashes indicated the rate of neutron production. The audience watched as preparatory shots produced a few specks of light on the screen. When it finally came time for the 50:50 D-T shot, the scintillator became a bright glowing square and cheers filled the auditorium. They had produced 4.3 MW of fusion power. It was more than four decades since Lyman Spitzer, there in Princeton, had dreamt of building a fusion reactor and started the project that became PPPL. The researchers there that day genuinely felt they had made history.

  TFTR did not, like JET, do two shots and then close down. Instead it embarked on an extended programme to study D-T fusion. Furth was determined to get to break-even and also set a first interim goal of 10 MW of fusion power which his staff went after tenaciously. The following year they were closing in, having got powers of more than 9 MW. But controllers of the machine were getting nervous because everything was being pushed to the limit: conditioning the vessel was exhaustive, they were using the highest possible magnetic field and plasma current, and the neutral beams were turned up to maximum. Then, under these conditions, they did a shot that ended in a huge disruption – this is where there is a sudden loss of containment and all the energy is dumped in the structure of the machine. There were microphones set up in the reactor hall so that they could hear what was going on over in the control room, which was in a separate building. The team heard a noise that sounded like the hammer of hell, followed by echoing thunder and then absolute quiet. The whole reactor building had been shaken. There was no serious damage, but after that they were much more careful. They tweaked the plasma to make it less prone to disruptions and later that year reached a power of 10.7 MW.

  During four years of experiments the Princeton researchers learned a huge amount about controlling a burning D-T plasma and set many more records. They were the first to demonstrate self-heating of the plasma by alpha particles. They set a record temperature of 510 million °C, a record plasma density of 6 atmospheres, among many other things. What TFTR didn’t achieve was break-even, only reaching a gain of Q=0.3. TFTR simply wasn’t big enough for that kind of performance: a larger plasma insulates the ions in the centre from the outside so they have more time to react, and TFTR’s traditional circular cross-section didn’t allow it to get the same sort of plasma currents that D-shaped reactors could.

  Then, in April 1997, TFTR was closed down. Many at the lab thought there was more that could have been done with the reactor. There were plans for further upgrades, but TFTR was an expensive machine to run, with its large staff and its tritium facilities, and the Department of Energy didn’t have the money to keep it going. What disturbed fusion researchers more was the fact that there were no plans for a replacement. PPPL was never normally slow to begin planning for the next machine. Back in 1983, when TFTR had only just started operating, researchers there were already working on the design of its successor which would study in detail the physics of burning plasmas heated by alpha particles and go all the way to ignition. But as the design of this Compact Ignition Tokamak progressed and its designers learned more from operating TFTR, it grew larger in size and cost. Then a review of the design ordered by the Department of Energy cast doubt on CIT’s ability to reach ignition and so the design was scrapped in 1990. Princeton responded with another plan, the Burning Plasma Experiment, which sought to address the deficiencies of CIT. But BPX also grew bigger and even more expensive than CIT and by this time the US was participating in the design of ITER, the international fusion reactor project, that would do everything BPX could do and more. So BPX was also abandoned in 1991. Princeton bounced back again with the Tokamak Physics Experiment, a smaller-scale machine that aimed to complement ITER by studying such issues as steady-state operation.

  This TPX, being small, was more in tune with the times. Since the golden era of the late 1970s and early 1980s, when Middle East oil embargoes had pushed the government to spend huge amounts researching possible alternative sources of energy, funding of fusion research had been following a steady downward trajectory. By the early 1990s, the DoE’s fusion budget was around half what it had been at its peak in 1977. Fusion scientists had had to temper their ambitions over the years, but worse was yet to come. The autumn of 1994 saw the ‘Republican revolution’ when the Republican Party won control of both houses of Congress for the first time in more than forty years. As they cast around looking for superfluous government spending to cut, fusion’s track record did not look good. Over forty years taxpayers had spent more than $10 billion on fusion and all those expensive machines had not even reached break-even.

  In the Republicans’ first budget, for 1996, fusion saw its roughly $350 million annual funding cut by more than $100 million. Something had to go and that meant first TPX and then TFTR itself. Some Princeton staff took the TPX design to South Korea where they helped the country build a scaled-down version as the Korea Superconducting Tokamak Advanced Research (KSTAR) facility, which produced its first plasma in 2008. But US researchers were left after 1997 with no major machine to work on. The DoE changed the emphasis of its fusion programme from one aimed at fusion energy to one investigating the science required to achieve fusion. Its main project was now ITER, but even that didn’t prove to be an easy relationship.

  * * *

  In the same year that TFT
R closed, JET researchers were agitating to have another crack at D-T operation but were being held back by the Euratom council. In the six years that had passed since their two 10% tritium shots they had fitted JET with a divertor and had experimented with it using deuterium-only plasmas. From the council’s point of view JET was proving to be a valuable research tool for learning how to control plasmas in a divertor configuration, able to test different strategies and materials. The plan was to fit another more advanced divertor but doing D-T experiments first would make such modifications more difficult. The council also feared expensive decommissioning costs when JET ended its working life if the vessel became very activated. The person in charge was now German plasma physicist Martin Keilhacker, Rebut having left in 1992 to lead the ITER design team. He supported the researchers’ view that really seeing what JET could do with D-T shots would provide invaluable data for ITER or any future burning plasma machine. And, he argued, JET’s remote handling system would soon be fully operational. The system’s many-jointed arm was capable of unfastening, removing and replacing components inside the vessel so the divertor could be upgraded without a person going inside.

  Keilhacker won the council round and in September 1997 JET broke TFTR’s record with a shot producing 16 MW of fusion power – a gain of Q=0.67. There was much less media hoopla surrounding this breakthrough compared to the shots in 1991 but it did make the newspapers. What didn’t get any column inches was another experiment performed on JET which was potentially much more important for future fusion energy production. The shots that achieved the highest power never lasted very long. That was because H-mode only works as long as the plasma density doesn’t go above a certain critical value. With the neutral particle beams pumping in more particles and H-mode keeping them trapped with its high confinement, the plasma density can only go up and after a couple of seconds H-mode breaks down and the shot terminates. Creating fusion with a succession of short pulses is not ideal for a power-producing reactor; much better would be one that can operate in a steady, unchanging fashion. Achieving that with H-mode would require a mechanism for leaking out some ions so that the density doesn’t go past the critical level. The JET researchers attempted to do this by exploiting a new plasma instability peculiar to H-mode known as edge-localised modes, or ELMs.

  ELMs are eruptions of plasma that allow fusion fuel to burst out of the plasma’s edge towards the wall of the reaction chamber. Because the confinement provided by H-mode is so good, pressure can build up in the plasma and ELMs are the plasma’s way of letting off steam. The eruptions come in all sizes but the larger ones are potentially damaging to the reactor as the ejected plasma can hit the vessel wall. Even if that doesn’t happen, plasma bursting through the separatrix will get swept by the open field lines down into the divertor and if it is a big burst the divertor can be damaged by the large amount of hot plasma.

  JET’s peak power shots were done in a way that suppresses ELMs, so that they got maximum confinement. But if you want your shot to last longer you can encourage small ELMs to occur so that some ions leak out and so keep the plasma density down. The JET researchers tried this, a so-called steady-state ELMy H-mode, and were able to produce pulses with a power of 4 MW but which lasted for five seconds. Although this configuration sacrificed some confinement and hence had a lower peak power, it provided a glimpse of a steady-state mode of operation that will likely be used on ITER.

  Some might view the big tokamaks as failures. They didn’t achieve their main goal of break-even – except, perhaps, JT-60 which reached an equivalent gain of Q=1.2 – and it took roughly a decade longer for them to reach their peaks than had originally been planned. Viewed another way, they presided over an era of huge progress in fusion science. They were designed only a few years after tokamaks were widely adopted around the world and their designers knew very little about what made tokamaks tick or how a large one would behave. Once they started and operators discovered how heating degraded confinement, their prospects looked very bleak. But through a mixture of luck and ingenuity they developed modes of operation – supershots and H-mode – that overcame that problem. While TFTR and JET didn’t reach break-even they got close enough to know that it was possible – with a bit more current or a slightly stronger field they might have made it.

  What the big tokamaks did show was that it was scientifically feasible for a controlled fusion reaction to produce more energy than it consumes, a goal that thousands of scientists had been pursuing ever since the likes of Peter Thonemann, Lyman Spitzer, Oleg Lavrentyev and others first dreamed of building a fusion reactor. And the machines did more than that: they showed that alpha particles will heat the plasma, which will be essential for creating a viable power reactor; and they demonstrated modes of operation, such as JET’s ELMy H-mode, that will be required for future reactors to run stably and safely for years on end.

  Euratom had planned to close JET in 1999 to free up resources for the construction of ITER. But ITER was not about to start construction; in fact the collaboration that designed it was on the point of breaking apart. With fusion’s great hope in a critical condition it seemed foolish to close down the next biggest tokamak, and so JET won a reprieve. Management of JET was handed over to the UK Atomic Energy Authority and the machine became a facility that fusion researchers from across Europe could come and use, mostly testing techniques that would be used on ITER when the giant was returned to health.

  CHAPTER 6

  Fusion by Laser

  THE FIRST SUSTAINED FUSION REACTION ON EARTH PRODUCing excess energy took place on 1st November, 1952, at precisely 7.15 a.m. The venue was the island of Elugelab in the Enewetak atoll of the South Pacific’s Marshall Islands. Nearly 12,000 people, military and civilian, were involved in setting up the test, which had the codename ‘Ivy Mike.’ They built a cryogenics plant on one of the other islands in the atoll to produce liquid deuterium for the fusion fuel. They built a 2.7-kilometre causeway linking four of the islands. For the device itself they built a large corrugated iron building. It needed to be big because the device, nicknamed ‘the Sausage,’ was more than 6m tall and 2m in diameter. Along with all the cryogenic equipment to keep the liquid deuterium cold, it weighed 74 tonnes.

  When the device was detonated, the blast was equivalent to more than 10 million tonnes of TNT, 450 times the power of the bomb dropped on Nagasaki in 1945. A mushroom cloud rose 37 kilometres into the air and spread out across 160 kilometres. Radioactive coral debris fell on ships moored 50 kilometres away. An hour later, after the mushroom cloud and steam had dispersed, a helicopter flew over the site. The islands of the atoll were stripped clean of vegetation except for Elugelab, of which nothing remained.

  Five thousand miles away in California Edward Teller, who had been the driving force behind the United States’ H-bomb programme, knew that Ivy Mike had been a success without having to wait for the phone call. A quarter of an hour before the scheduled time of the test he had walked across the grounds of the University of California, Berkeley, to Haviland Hall and sat down by the seismometer in its basement. The machine shone a fine point of light onto a photographic plate to record any movements of the Earth. Teller sat in darkness watching the bright spot and, at precisely the time he had predicted it would happen, the light started to dance around wildly on the plate as the Earth shook in response to the blast on the far side of the Pacific. This completed his ten-year-long campaign to ensure that the United States possessed the most devastating weapon imaginable before its enemies did. Teller sent a telegram to his colleagues at the Los Alamos laboratory containing just the pre-arranged phrase: ‘It’s a boy.’

  In 1941 American physicists first began talking about the possibility of constructing a nuclear fission weapon, or A-bomb, amid the concern that Germany may already be well on the way to constructing one. Then Enrico Fermi casually mentioned to Teller that perhaps it would be possible to use an A-bomb to ignite a more powerful fusion weapon. Teller became obsessed with the idea. Soon bot
h men were enrolled into the Manhattan Project and at its newly built headquarters at Los Alamos, Teller argued that the project should also try to build a fusion bomb, or ‘Super,’ at the same time. His colleagues were not persuaded and the A-bomb remained the focus, but Teller often ignored the work assigned to him so that he could continue to work on the Super. Ironically, the person who ended up taking over Teller’s unfinished work was Klaus Fuchs, who was later unmasked as a Soviet spy.

  After bombs had been dropped on Hiroshima and Nagasaki, Teller was all for moving straight on to develop the Super. He feared that the Soviet Union would soon catch up with the US in nuclear weapons technology and he wanted his adopted country to hold onto the advantage it had. But few others were interested. Many participants in the Manhattan Project, having seen the destruction their creation had wreaked in Japan, were appalled at the idea of building a weapon a thousand times more powerful. Many argued that the only feasible use for such a weapon would be to kill huge numbers of civilians; hence it was a weapon of genocide. Some simply thought such a bomb wouldn’t work. Most veterans of the project returned to their universities after the war ended.

  Then came the first Soviet A-bomb in 1949 and President Truman’s crash programme to develop the Super as quickly as possible. The problem was, Teller’s design didn’t work. He had assumed that the intense heat created by an A-bomb as it ignited would be enough to spark fusion in nearby deuterium-tritium fusion fuel. He and his colleagues at Los Alamos tried out various designs that attempted to get the fusion fuel as close as possible to the exploding A-bomb, such as a spherical A-bomb surrounded by a layer of D-T or the reverse, a sphere of D-T surrounded by a hollowed-out fission bomb. But according to their experiments and calculations, this was not enough to ignite a fusion burn.