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Physics

Energy from the stars

Brazilians and Europeans seek control of nuclear fusion

EFDA / JETIn the shape of a ring: the plasma chamber in JET, the biggest tokamak in activityEFDA / JET

Five decades ago the popular science journals in the United States boasted that in less than 50 years the source of electricity in the world would be the clean and practically inexhaustible energy that makes stars shine: nuclear fusion. Time has passed and today there are only nuclear fission power stations that produce energy by breaking down heavy atomic particles. A fusion power station, on the contrary, would function by extracting energy from the union of two nuclei of hydrogen, the most abundant chemical element in the Universe. In a partnership with European groups, Brazilian researchers are working toward transforming fusion into reality.

Fusion occurs in the stars when hydrogen nuclei in the form of gas are compressed by gravity and reach temperatures of millions of degrees. To do the same on Earth, however, this electrically charged gas (plasma) needs to be confined, using magnetic fields generated by machines called tokamaks, and heated. Here, the reactor fuel would be two variants of hydrogen: deuterium, which can be extracted from seawater, and tritium, produced from lithium particles, whose reserves on the planet would guarantee the functioning of power stations for millions of years.

This all sounds so much like science fiction that it is with a certain degree of suspicion that researchers are heard to make the same statement as in the past; that the first fusion power station will function 50 years hence. This time, however, the chances of the idea materializing are greater. Since the invention of the tokamak by the Soviets in the 1960’s, the performance of these machines has improved ten thousand times. In 1991, the biggest tokamak in activity until now – the Joint European Torus (JET), installed in Culham, in the United Kingdom – managed to achieve the first controlled nuclear fusion reaction in history. The problem was that the experiment used more energy than it generated.

Physicists today believe that the efficiency of tokamaks (there are other types of equipment for trapping plasma, but none are as effective) needs to be improved by a further ten times to reach the point at which the amount of energy released in fusion reactions is greater than the amount consumed. This is the objective of the International Thermonuclear Experimental Reactor (Iter), under construction since 2007 at Cadarache, in France. The consortium responsible for the project, formed by the European Union, China, South Korea, the United States, India and Japan, calculates that it will spend US$ 13 billion assembling this tokamak, more than the amount consumed in creating the LHC, the world’s biggest particle accelerator.

Iter will be 61 meters high and as heavy as three Eiffel Towers. It will contain a volume of plasma eight times greater than the JET and when it is ready in 2019 it should generate 500 megawatts of power, while consuming only 50 megawatts. Assuming that everything runs smoothly with Iter, the optimists are counting on the inauguration of the first experimental fusion power station, called Demo (from demonstration), in 2040. “This is the prospect according to the optimists; for the pessimists, energy production by nuclear fusion is intangible,” says physicist Ricardo Viana, from the Federal University of Paraná, recognizing that it will not be easy to achieve this final increase in the performance of tokamaks.

060-063_FusaoNuclear_186In January of this year he and five colleagues made a small contribution to the challenge. In the journal Philosophical Transactions of The Royal Society A they published a study in which they calculated how particles of plasma behave close to the wall of the chamber of a tokamak and escape the magnetic trap that imprisons them, hitting some points on the wall more often than others. The impact of the electrically charged particles accelerates the wear and tear on the wall and compromises the functioning of the machine.

The work of Viana and collaborators was one of the elements that clarified the phenomenon, discovered five years ago in tokamaks in Europe and the United States and which enabled a proposal to solve the problem. Using the tokamak at the University of São Paulo (USP), physicist Ivan Nascimento and his colleagues showed that it is possible to lessen this leakage with the help of electrical fields.

Increasing the control over plasma is the main challenge in tokamaks. Far from flowing smoothly as it circulates in these machines, plasma behaves like a sea that is being churned up by a storm. Its movement is turbulent, especially on the edge of the region of confinement, where the density, temperature and electromagnetic fields that keep it imprisoned fluctuate a lot. The turbulence is such that new ways are always being discovered by which the plasma can escape and cool down. Until now the maximum time that the plasma can be maintained without losing energy does not exceed fractions of a second.

Iberê Caldas, a physicist at USP and coauthor of the article signed by Viana, gives an example of a recent solution for the escape of plasma. When developing Iter, North American researchers discovered how to control a phenomenon capable of causing violent plasma explosions, similar to the eruptions on the surface of the Sun, which could damage the reactor.

The solution was to modify Iter’s design and include chaotic magnetic field generators that, by the calculations of the physicists, will keep the eruptions from occurring. “This alteration will cost more than – 100 million and has led to a postponement of more than a year in the project,” says Caldas. He, Nascimento, Viana and a further 130 researchers from 15 Brazilian institutions are currently taking part in the National Fusion Network (RNF), an organization set up in 2006 by physicist Sérgio Rezende, then Brazil’s minister of Science and Technology, that is beginning to mature now. Another physicist, Ricardo Galvão, the technical and scientific coordinator of the RNF and director of the Brazilian Physics Research Center (CBPF) in Rio de Janeiro, says that the idea of creating the network came about after a committee of European researchers visited Brazil and assessed the country’s potential for contributing to Iter.

The committee identified that although there is significant scientific production in plasma physics in Brazil, efforts were not coordinated. Each research group did its own work independently from other groups, in the form of short-term projects. “To work on an international project of this size it’s necessary to have a commitment of five or ten years and have the capacity to build equipment here [in Brazil] for installation out there [at Iter],” says Galvão, who is a member of the team at the Plasma Physics Laboratory at USP.

Plasma: ions captured by magnetic fields

EFDA / JETPlasma: ions captured by magnetic fields EFDA / JET

The network functions with funds from the Studies and Projects’ Funding Agency (Finep), which in 2010 approved a little over R$ 1 million for its research projects. Some of these studies involve collaboration with European laboratories, established by means of an agreement signed in 2009 between Brazil and the European Atomic Energy Community. Although it is already in force, the agreement is awaiting ratification by the National Congress.

In a partnership with German researchers, Brazilian engineers, including Hugo Sandim, from the Lorena School of Engineering, and Angelo Padilha, from the Polytechnic School, both of which are part of USP, are working on characterizing materials to be used in the walls of the plasma chamber of Demo, the reactor of the generation subsequent to Iter. Made from a family of steels called Eurofer, the material needs to support proximity with plasma at a temperature of 150 million degrees (10 times the temperature at the center of the Sun), in addition to being bombarded with highly energetic neutrons and possible plasma discharges.

The researchers already know, however, that the steel cannot remain exposed to plasma. There is the risk that the heavy nuclei of the metal will end up inside it, which can destabilize the magnetic fields in the tokamak and destroy the confinement in such a way that the whole of the electric current of the plasma (100 times greater than the lightning in a storm) will touch a point on the wall all at once. To avoid damage, specialists have developed a lining of beryllium tiles. Beryllium atoms are light enough not to interfere with the plasma and at the same time sufficiently resistant to be able to support the neutrons and the high temperatures.

The lining should begin being tested in the JET as from September and will count as a Brazilian contribution. During the trials a super-fast infrared camera will observe the wear and tear on the tiles. However, the infrared radiation close to the wall is so great that Galvão compares the task to observing a minute object passing in front of the Sun. To analyze the images in real time, the JET researchers will use a computer program developed by the brothers Marcelo and Márcio Albuquerque from the CBPF.

Alfven waves
Another Brazilian project at the JET intends studying a further phenomenon capable of frustrating Iter’s plans. The physicists hope that the nuclei of helium formed in the fusion will remain in the plasma and collide with electrons and other nuclei. In this way they would help to heat the plasma and support conditions for more fusion reactions. Helium, however, excites the electromagnetic waves in the plasma – the so-called Alfven waves – that, depending on their duration, may expel the helium and interrupt the fusion.

Researchers from USP and colleagues from the Massachusetts Institute of Technology in the United States and from the École Polytechnique Fedérale de Lausanne (EPFL), in Switzerland, are planning to assemble an Alfaven wave stimulation and detection system at the JET by December to measure how fast they disappear. “They’ve made tremendous progress,” says Patrick Blanchard, the scientific coordinator at JET, about the improvement that engineers from USP have made in the antennas that generate Alfven waves. “It would have been difficult without them.”

This international agreement also enabled the Europeans to come to Brazil. Although smaller machines than the JET and Iter do not reach fusion conditions, the three Brazilian tokamaks – one at USP, another at the State University of Campinas and a third at the National Space Research Institute (Inpe) – are contributing with studies on plasma turbulence. Researchers from USP and the Instituto Superior Técnico de Lisboa [Lisbon Higher Technical Institute], for example, have created systems for measuring the turbulence in the tokamak at USP .

National network
In addition to formalizing the agreement with the Europeans, the members of the RNF are waiting for the setting up of a new research center: the National Fusion Laboratory (LNF), affiliated to the National Nuclear Energy Commission (Cnen), which is to be built in Cachoeira Paulista, in São Paulo State.

There is, however, a bureaucratic impasse to the setting up of the laboratory. The legal advisers of the institutions involved have not yet reached an agreement as to the need to submit the decision to set up the LNF to the National Congress. Edson Del Bosco, a physicist from Inpe’s Associated Plasma Laboratory, is anxiously awaiting the start of construction work, which still does not have a starting date. He hopes that the LNF will act as a catalyst of funds and personnel, thus breathing a new breath of life into small research groups like his and into others that are associated with the laboratory. “If the LNF is not set up there’s no way for us to progress,” he says.

Del Bosco and Galvão hope that the problem will be solved right at the beginning of the term of office of the new president of the Cnen, engineer Angelo Padilha, who is a member of the RNF and was officially sworn in on July 7. Padilha say that one of his priorities at the Cnen is to set up the LNF. According to Galvão, the plan is to start the activities of the LNF by making improvements in Inpe’s tokamak. Some members of the RNF are considering buying or building a bigger tokamak later, while others, like Galvão, believe it is not worth it because of the high cost. “If there’s strong interaction with the Europeans and access to their machines, it will be better to have a small tokamak for training people and using the laboratory for building equipment that we would install in their laboratories,” he says.

Members of the RNF agree on one point: fusion is a long-term investment, which Brazil cannot forgo. After all, it is not known what the country’s power demands will be in 2100. “We need to master the technology and the scientific knowledge so we don’t have to buy a reactor in the future,” says Galvão. “If nuclear fusion works, the Iter consortium will be the owner of the world’s energy.”

The project
Alfven heating, improved confinement regimes and stability in the tokamak TCABR (nº 2002/03632-3); Type Thematic Project; Coordinator Ricardo Osório Galvão – IF/USP; Investment R$ 1,004,053.90 (FAPESP)

Scientific article
VIANA, R.L. et al. Fractal structures in nonlinear plasma physics. Philosophical Transactions of the Royal Society A. v. 369, p. 371-95. 2011.

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