Piece of the Sun : The Quest for Fusion Energy (9781468310412) Page 13
Up until this point, fusion devices were not built to be genuine reactors because they generated so few fusion reactions. Their main aim was to practice confining and heating plasma. Now that devices were getting closer to producing lots of fusion reactions, reactor designers had to take into account the copious energy and particles the reactions would produce. Fusing a deuterium nucleus and a tritium nucleus produces two things. First is a high-energy neutron which has 80% of the energy released by the reaction so it will be moving very fast. Because neutrons are electrically neutral they are not affected by the tokamak’s magnetic field and so zap straight out and bury themselves in the tokamak wall or something else nearby, converting their kinetic energy into heat. In a power reactor the idea is to get those neutrons to heat water, raise steam, and use that steam to drive a turbine, turn a generator and create electricity.
The other thing produced in the reaction, carrying the remaining 20% of the energy, is a helium nucleus, otherwise known as an alpha particle. The alpha particle is charged so it will follow a helical path around magnetic field lines in the tokamak just as the ions and electrons of the plasma do. Capturing the alpha particles in the field serves a useful purpose: as they twirl around in the plasma they knock into other particles, transfer energy and generally heat things up. The designers of fusion reactors very much wanted to exploit this effect. If you can get alpha particles to heat up your plasma, that will help to keep the fusion reaction going and may even make other heating methods, such as neutral particle beams and radio-frequency waves, unnecessary.
The difficulty is that the newly created alpha particles are heavier than hydrogen and moving fast, so their spirals will be much wider. If the plasma vessel is too small, the spiralling alphas won’t get very far before hitting the wall. A stronger magnetic field will make the alpha particle spirals smaller, and the field is created in part by the plasma current. So reactor designers could derive a formula for successful alpha particle heating: for a given size of plasma vessel, there is a minimum plasma current that will create a strong enough field to keep the alpha particles within that vessel.
The JET study group reported back to the Groupe de Liaison in May 1973 and recommended that Euratom should build a tokamak around 6m across which, to contain alpha particles, would need to carry a current of at least 3 million amps (MA). This was a huge leap from the tokamaks of the day. France’s TFR was just 2m across and carried 400,000 amps and it was only just being finished. Physicists had no real idea how plasma would behave with 3MA of current flowing through it. But the excitement about tokamaks was so great in the early 1970s that Palumbo acted on the study group’s suggestions straight away and started to assemble a team to work out a detailed design for such a reactor. The obvious man to lead that effort, the man who had just finished building the world’s most powerful tokamak, was Paul-Henri Rebut.
In the United Kingdom, Sebastian Pease’s Culham laboratory was struggling. Researchers there had kept on working with ZETA during the 1960s and had done some good science. But attempts to build large follow-on machines – ZETA 2 and another one called ICSE – were thwarted by the government. Researchers had to content themselves with smaller devices. As the decade wore on, however, funding to the lab was repeatedly cut. Pease realised that if his lab was ever going to get involved in operating a large device again, it would have to be through collaboration with Britain’s European neighbours. But there was a problem: at that time Britain was not a member of the EEC or Euratom. Nevertheless, Pease talked to Palumbo and he allowed Pease and his colleagues to attend meetings of the Groupe de Liaison and join in discussions about JET.
By 1973, when Palumbo was putting together a team to design JET, Britain had joined the EEC and Euratom, and hence Pease was able to offer Culham as a base for the JET design team. So it was that in September 1973, only a few months after the study group proposed that JET should be built, Rebut set sail for England to begin the work. And he did literally set sail. Reluctant to leave behind a yacht that he had designed and built himself but which was not quite finished, Rebut sailed across the English Channel to take up his new job.
Initially housed in wooden huts left over from Culham’s time as a World War II airbase, the JET team had a daunting task ahead of them, and just two years to do it in. With the understanding of tokamaks still so sketchy there were two routes they could take: the safe, conservative route of simply scaling up in size from existing, successful machines such as TFR; or the more risky path of trying out some untested ideas. With the flamboyant Rebut in charge it was always going to be the latter. But the designers were constrained by a number of factors: disruptions and other instabilities, for example, limited the plasma’s density and the current that could flow through it. There were practical considerations, such as the strength of magnets. And there was cost.
Bearing all of these issues in mind, the team came up with a design for a tokamak that was 8.5m across and the interior of the plasma vessel was twice the height of a person. The volume of the plasma vessel was 100 cubic metres (m3), a vast space compared to TFR’s 1m3. The current flowing through JET’s plasma (3.8MA) would be ten times that in TFR.
Earlier tokamaks – designed principally to study plasma – did not use the most reactive form of fusion fuel, deuterium-tritium. JET would be different but this added a hornet’s nest of problems to the project. Tritium is a radioactive gas which, because it is chemically identical to hydrogen, is easily assimilated into the body. So extreme care has to be taken to avoid leaks and every gram of it has to be accounted for. Carrying out deuterium-tritium, or D-T, reactions also produces a lot of high-energy neutrons. When these collide with atoms in the reactor structure it can knock other protons or neutrons out of their nuclei, potentially turning them radioactive. So over time, the interior of the tokamak acquires a level of radioactivity from the neutron bombardment. The levels are nothing like in a fission reactor, but they are enough to make it dangerous for engineers to go inside to carry out repairs or make alterations. JET had to be designed so that any work inside the vessel could be done from outside with a remote manipulator arm, even though such machines were only in their infancy at that time.
Everything about the design was big and ambitious, but one innovation stood out. Rebut decided to make the shape of the plasma vessel D-shaped in cross-section rather than circular. Part of the motivation for this was cost. The magnetic fields required for containment exert forces on the toroidal field coils, the vertical ones that wrap around the plasma vessel. These magnetic forces push the coils in towards the central column of the tokamak and are stronger closer to the centre. JET would require major structural reinforcement to support the toroidal field coils against these forces which would be very expensive. So, Rebut mused, why not let the coils be moulded by the magnetic forces? If left to find their own equilibrium, the coils would become squashed against the central column into a D-shape and stresses on them would be greatly reduced. So Rebut designed a tokamak with D-shaped toroidal field coils and a D-shaped plasma vessel inside them. In cross-section the vessel was 60% taller than it was wide. Overall, the tokamak now looked less like a doughnut and more like a cored apple.
But more importantly Rebut thought a D-shape would get him better performance. In 1972 the Russian fusion chief Lev Artsimovich and his colleague Vitalii Shafranov calculated that plasma current flows best when close to the inside wall of a plasma vessel – close to the central column. So if the plasma vessel was not circular in cross-section but was squashed against the central column, more plasma current would gain from the most favourable conditions. The Russians were in the process of testing the idea but at the time there was little proof that it would work. Rebut was convinced that the key to confinement was a high plasma current and a D-shape, he believed, could allow him to go far beyond the 3MA in JET’s specification. He guessed that the Groupe de Liaison would not be persuaded by the Russians’ theoretical prediction alone, so adding the issues of cost and engineering wou
ld help his case. He was right to be worried. When the JET team presented its design in September 1975, there was vigorous debate about the size of the proposed reactor, the D-shaped plasma vessel, the cost and more besides. Palumbo admitted that he would have preferred the tried-and-tested circular vessel but he trusted Rebut and his team and argued for their design.
Such was the persuasiveness of Rebut that the various Euratom committees eventually agreed to go ahead with JET pretty much as described in the design report. The Council of Ministers, the key panel of government representatives that oversaw the EEC and Euratom, also approved the plan. Constructing JET was predicted to cost 135 million European currency units (a forerunner of the euro) of which 80% was to come from Euratom coffers and the rest from member governments. All that remained was for the council to decide where it was to be built. Although there were technical requirements for the site, this was predominantly a political decision. The fifty-six-strong JET design team waited at Culham to hear the decision. Most of them would move straight to new jobs helping to build JET, so there was little point returning to their home countries.
Hosting such a high-profile international project was viewed as a prize by European nations and soon there were six sites vying for the honour: Culham; a lab of France’s CEA in Cadarache; Germany offered its fusion lab at Garching and another site; Belgium offered one; as did Italy with the Euratom-backed fission lab at Ispra. In December 1975 the Council of Ministers debated the site issue for six hours and came away without a decision. So the politicians asked the European Commission, the EEC’s executive body, to make a recommendation. The commission opted for Ispra, but when the council met again in March Britain, France and Germany vetoed this suggestion.
The council met again several times in 1976 but still without any resolution of the issue. Rebut and the team at Culham were getting desperate. Some were accepting jobs elsewhere while others were simply returning to their old pre-JET jobs at home. The European Parliament demanded that the matter should be settled. Politicians began to talk of the project being on its deathbed. The council discussed whether they should abandon their normal rule of making unanimous decisions and decide it by a simple majority, but they failed to decide on that too. All they did manage to do by this time was whittle the list down to two candidate sites: Culham and Garching. The frustrated scientists at Culham sent petitions to the council; their families sent petitions to the council. But by the summer of 1977 the game was up and Rebut and his Culham host Pease decided it was time to wind up the JET team.
On 13th October, while the team was still disbanding, fate intervened. A Lufthansa airliner en route from Mallorca to Frankfurt was hijacked by terrorists from the Popular Front for the Liberation of Palestine. They demanded $15 million and the release of eleven members of an allied terrorist group, the Red Army Faction, who were in prison in Germany. Over the following days, the hijackers forced the plane to move from airport to airport across the Mediterranean and Middle East before finally stopping on 17th October in Mogadishu, Somalia, where they dumped the body of the pilot – whom they had shot – out of the plane. They set a deadline that night for their demands to be met. German negotiators assured them that the Red Army Faction prisoners were being flown over from Germany but at 2 a.m. local time a team of German special forces, the GSG 9, stormed the plane. In the fight that followed, three of the four terrorists were killed and one was wounded. All the passengers were rescued with only a few minor injuries.
So what was the connection with JET? Germany created the GSG 9 in the wake of the bungled police rescue of Israeli athletes after their kidnap by Palestinian terrorists at the Munich Olympics in 1972. For training, the GSG 9 went to the world’s two best known anti-terrorist groups: Israel’s Sayeret Matkal and Britain’s Special Air Service (SAS). Mogadishu was the GSG 9’s first operation and two SAS members travelled with the group as advisers, supplying them with stun grenades to disorient the hijackers.
A home at last: the JET design team, with Paul-Henri Rebut at front centre, celebrates the decision to build JET at Culham, a week after the end of the Mogadishu hijack.
(Courtesy of EFDA JET)
The whole hijack drama had been followed with mounting horror, especially in Germany. When the news of the rescue broke on 18th October the country was awash with relief and euphoria, especially when a plane arrived back in Germany carrying the rescued passengers along with the GSG 9, who were welcomed as heroes. Into this heady atmosphere stepped the British Prime Minister, James Callaghan, who arrived in Bonn on the same day for a scheduled summit meeting and was greeted by German chancellor Helmut Schmidt with the words: ‘Thank you so much for all you have done.’ There were a number of EEC matters that divided Britain and Germany at the time and in the happy atmosphere of that summit meeting many of them were put to rest, including the question of JET’s location. A meeting of the Council of Ministers was hastily called a week later. The result was phoned through to Culham around noon and the champagne was, finally, uncorked. At last JET was ready to be built and Rebut and what remained of his team didn’t have to move anywhere.
Long before climate change became widely recognised as a threat to our future, an environmental movement grew up in the United States which drew attention to the pollution of the atmosphere by the burning of fossil fuels. This public pressure led to the 1970 Clean Air Act and the creation of the Environmental Protection Agency. At the same time, America’s electricity utilities were having trouble keeping up with the soaring demand for power, leading to often serious blackouts and brownouts. The Nixon administration responded by making the search for alternative energy sources, with less environmental impact, a national priority. The Atomic Energy Commission was pinning its hopes on the fission breeder reactor which it had been developing for some time. The AEC argued that the breeder produced less waste heat than the light-water fission reactors that power utilities were building at the time, and burned fuel more efficiently. But the increasingly vocal environmentalists didn’t buy it. As far as they could see, breeder reactors had the same safety concerns as light-water machines plus their plutonium fuel was toxic, highly radioactive and a proliferation risk.
With the government looking for alternative energy sources and the public suspicious of nuclear power, fusion scientists suddenly found themselves in demand. Fusion was seen as a ‘clean’ version of nuclear energy and the idea of generating electricity from sea water seemed almost magical. Researchers from Princeton and elsewhere were now being interviewed by newspapers, courted by members of Congress, and the new tokamak results meant that they really had something to talk about. As if on cue, Robert Hirsch, someone very well suited to make the most of this new celebrity, was put in charge of fusion at the AEC. Hirsch was in his late 30s; he wasn’t a plasma physicist, but he was a passionate advocate of fusion and he knew how to play the Washington game: he was at home in the world of Senate committees, industry lobbyists and White House staffers. In 1968 he had been working with television inventor Philo T. Farnsworth on a fusion device using electrostatic confinement and applied to the AEC for funding. Instead, Amasa Bishop hired him. He worked under Bishop and his successor Roy Gould but was always frustrated by the relaxed, collegial approach of the fusion programme. In Hirsch’s mind, fusion should be the subject of a crash development programme like the one that sent Apollo to the moon.
In 1971, Hirsch got his chance. Leadership of the AEC changed from nuclear physicist Glenn Seaborg to economist James Schlesinger, then assistant director at the Office of Management and Budget. Schlesinger wanted to counter criticism at the time that the AEC was simply a cheerleader for the nuclear industry; he wanted to diversify into other types of energy. One of his first changes was to promote the fusion section – which at that time was part of the research division – into a division in its own right. Gould, an academic from the California Institute of Technology, stuck to it for around six months and then stood down. Hirsch, like Schlesinger, was interested in planning and
effective management. He was a perfect fit and took over as head of the fusion division in August 1972.
At that time, the fusion division was a tiny operation: just five technical staff and five secretaries. Its role and operations had not changed much since the 1950s. The direction of research and its timetable was pretty much decided by the heads of the labs. The fusion chief at the AEC acted as referee between the competing labs and was their champion in government. Hirsch had very different ideas. First he wanted more expertise in the divisional headquarters so that decisions about strategy could be made there. Within a year he had more than tripled the technical staff and by mid 1975 the division boasted fifty fusion experts and twenty-five support staff. He created three assistant director posts in charge of confinement systems, research, and development and technology. Now the lab heads had to report to the various assistant directors, not to Hirsch himself.
Hirsch also wanted the programme to be leaner and more focused, and that meant closing down some fusion devices which were not helping to advance towards an energy-producing reactor. Before the end of 1972 he closed down two projects at the Livermore lab: an exotic mirror machine called Astron and a toroidal pinch with a metal ring at the centre of the plasma held up by magnetic forces, hence its name, the Levitron. The following April he closed another mirror machine, IMP, at Oak Ridge. These terminations sent shock waves through the fusion laboratories. It was the first time that Washington managers, rather than laboratory directors, decided the fate of projects.
Hirsch knew that if fusion was going to be taken seriously by politicians it needed a timetable; an identifiable series of milestones towards a power-producing reactor. He set up a panel of lab directors plus other physicists and engineers to sketch out such a plan. The first milestone they defined was scientific feasibility, showing that fusion reactions could produce as much energy as was pumped into the plasma to heat it – a state known as break-even. The second would be a demonstration reactor, one that could produce significant amounts of excess energy for extended periods. After that would come commercial prototypes, probably developed in collaboration with industry. The panel suggested that the first goal could be achieved sometime around 1980-82, while a demonstration reactor might be built around 2000. There was some disquiet about this timetable at the fusion labs. They weren’t sure eight or ten years was enough to get to scientific feasibility, but at Hirsch’s urging this plan became official division policy.