Galeria

Recent fusion experiments on the DIII-D tokamak at General Atomics (San Diego) and the Alcator C-Mod tokamak at MIT (Cambridge, Massachusetts), show that beaming microwaves into the center of the plasma can be used to control the density in the center of the plasma, where a fusion reactor would produce most of its power. Several megawatts of microwaves mimic the way fusion reactions would supply heat to plasma electrons to keep the "fusion burn" going.

The new experiments reveal that turbulent density fluctuations in the inner core intensify when most of the heat goes to electrons instead of plasma ions, as would happen in the center of a self-sustaining fusion reaction. Supercomputer simulations closely reproduce the experiments, showing that the electrons become more turbulent as they are more strongly heated, and this transports both particles and heat out of the plasma.

"We are beginning to uncover the fundamental mechanisms that control the density, under conditions relevant to a real fusion reactor," says Dr. Darin Ernst, a physicist at the Massachusetts Institute of Technology, who led the experiments and simulations, together with co-leaders Dr. Keith Burrell (General Atomics), Dr. Walter Guttenfelder (Princeton Plasma Physics Laboratory), and Dr. Terry Rhodes (UCLA).

The experiments were conducted by a team of researchers as part of a National Fusion Science Campaign. This new program enables research on one fusion experiment to be expanded to device another with complementary instrumentation and capabilities. "The National Campaign has increased the impact of our work, with added benefit to the fusion program," says Dr. Ernst. "Comparing Alcator C-Mod and DIII-D tests our new predictions that particle collisions strongly reduce this type of turbulence. The collision rate varies by a factor of ten between the two machines," says Ernst.

The experiments and simulations suggest that trapped electron turbulence becomes more important under the conditions expected in self-heated fusion reactors. The structure of the simulated turbulence during the electron heating is shown at right. The simulations closely matched detailed measurements of the actual turbulence in the 20cm diameter inner core. "We discovered sheared flows also drive turbulence in the inner plasma core, but as we approached conditions where mainly the electrons are heated, the usual plasma flow is reduced and pure trapped electron turbulence begins to dominate," says Dr. Guttenfelder, who did the supercomputer simulations for the DIII-D experiments, along with Dr. Andris Dimits (LLNL). Measurements revealed a band of fluctuations, separated by a constant frequency interval, like harmonics in a musical note. "These new coherent fluctuations appear to be consistent with the basic trapped electron instability that grows stronger during heating, " says Dr. Rhodes.

In a self-heated fusion reactor, fusion reactions produce very energetic alpha particles that collide with electrons as they move through the plasma. The collisions heat the electrons by imparting random thermal motion. The electrons in turn collide with and heat cooler deuterium and tritium fuel ions to fusion temperatures. However, turbulent eddies can swirl the particles and energy away from the hot core toward the cooler edge, where they eventually are lost to the walls of the chamber.

These experiments are part of a larger systematic study of turbulent energy and particle loss under fusion-relevant conditions. "It's important to understand what drives the turbulence, and how it can be controlled and minimized, to find new ways of operating tokamaks that exploit that knowledge," says Dr. Burrell. By comparing detailed turbulence measurements with simulations, researchers hope to understand how turbulence controls the core temperature under fusion conditions.

Source: EurekAlert

On 9 October 2014 the European Commission officially launched the European Consortium for the Development of Fusion Energy, EUROfusion for short. EUROfusion manages the European fusion research activities on behalf of Euratom, which awards the appropriate grant to the consortium. The new consortium agreement will substitute the fourteen year-old European Fusion Development Agreement (EFDA), as well as 29 bilateral Association agreements between the Commission and research institutions in 27 countries. The Grant Agreement (contract) provides €424M in funding from the Euratom Horizon 2020 programme 2014-18 and the same amount from Member States, adding up to an overall budget of €850 million for 5 years.

The launch of EUROfusion was celebrated with Europe’s fusion research community in the heart of the European Quarter, the Solvay Library. Robert-Jan Smits, Director-General DG Research & Innovation, opened the event in the presence of the Heads of EUROfusion Research Units, Members of the European Parliament and representatives of the European Commission. In his welcome address, Vice-President and European Commissioner for Energy, Günther Oettinger noted that “Europe sets the path to commercialization of fusion energy.” Prof. Sibylle Günter, Scientific Director of Max-Planck-Institute for Plasmaphysics, Germany, and Chair of the EUROfusion General Assembly, introduced the EUROfusion consortium and its research programme. She also thanked everybody who contributed to the sucess. Günter presented the roadmap to the realisation of fusion energy, which forms the basis for all EUROfusion activities. “The EUROfusion work plan is designed to exploit synergies and ensure excellence in the best possible way,” she pointed out. In his keynote address about fusion energy and fusion research in general, Prof. Steve Cowley, Director of Culham Centre for Fusion Energy (CCFE), UK, said: “It it is a wonderful time to work in fusion and the most important”.

At mid-day, Robert-Jan Smits and Sibylle Günter signed the grant agreement between EUROfusion and the European Commission, thus marking the official start of the Consortium. “It is an historic event as this is the European research organisation with the most member states, “ said EUROfusion Programme Manager Prof. Tony Donné. “For the first time we are bringing together 27 countries to work on a common scientific goal – fusion electricity by 2050.”

Dr. András Siegler, Director for Energy Research, DG Research & Innovation, opened the afternoon session. “Now that all contracts are signed we can focus on the research,” he said. Former EFDA Leader Prof. Francesco Romanelli looked both back and forward in this talk about the transition from EFDA to the Joint Programme under EUROfusion. He pointed out the pragmatic approach of Fusion Roadmap. “My advice,” he said, “don’t look for the ultimate solution.” A panel discussion between Tony Donné, Dr. Thomas Mull, AREVA and member of the Fusion Industry Innovation Forum, Dr. Catherine Cesarksy, former Chair of CCE-FU (Consultative Committee for the EURATOM specific research and training in the field of nuclear energy (fusion)), Prof. Niek-Lopes Cardozo, Chair of the Fusion Education Network FuseNet and Dr. Sandor Zoletnik, Head of the RMI-Institute for Particle and Nuclear Physics, Budapest, completed the event.

Background:
The formation of EUROfusion marks a big step forward for Europe’s quest to develop fusion power as a climate-friendly energy source that will contribute to meet a growing global energy demand. The EUROfusion Consortium enables Europe’s national laboratories to pool their resources even more efficiently – a measure which became necessary to meet the challenge of increasingly complex and large-scale projects such as ITER and DEMO. The preparation for such a joint fusion programme started in 2012. All EU research laboratories jointly drafted a detailed goal-oriented programme to realise fusion energy by 2050. This programme, known as the ‘Roadmap to the Realisation of Fusion Electricity’ outlines the most efficient path to fusion power. The roadmap has two main aims: Preparing for ITER experiments in order to ensure that Europe makes best possible use of ITER and to develop concepts for a fusion power demonstration plant DEMO. The necessary research towards reaching these aims is carried out by universities and research centres within the current European Framework Programme Horizon 2020. More than before does the programme involve industries in the process of designing components and finding technical solutions.

Source: euro-fusion.org

Nuclear fusion could become the main source of energy in the second half of this century, and Europe is well-positioned to lead the way as long as it manages its resources correctly, according to the people overseeing the research.

‘The world is really looking at us,’ said Professor Sibylle Günter, scientific director of the Germany-based Institute for Plasma Physics, which is coordinating EUROfusion, a new initiative pooling fusion research in Europe due to be officially launched on 9 October. ‘Europe has the opportunity to strengthen its world-leading position here because we have such a broad and well-organised fusion programme.’

Scientists believe nuclear fusion has the potential to meet a large proportion of the world’s energy demand in a cost-effective way. Unlike nuclear fission, which powers the nuclear reactors used today, nuclear fusion does not produce long-lived radioactive waste and is not subject to the same safety concerns.

Instead, nuclear fusion uses the same energy that powers the sun – heating hydrogen atoms to millions of degrees Celsius so that they fuse together into helium, generating energy in the process. However, the big challenge is maintaining the conditions and extremely high temperatures needed for the fusion reaction, and extracting useful heat for electricity generation.

To solve this, regions representing over half the world’s population have joined forces to build ITER – the International Thermonuclear Experimental Reactor – in the hills of Provence, southern France, in a concerted effort to show that the technology can produce at least ten times more energy than it consumes.

The doughnut-shaped reactor, known as a tokamak, which will burn at ten times the temperature of the core of the sun, is expected to start producing a significant net gain in energy. It should produce a power output equivalent to that of a medium-sized power plant.

The success of ITER is crucial. Once the viability of nuclear fusion as a realistic source of energy has been demonstrated, the idea is to use the lessons from ITER to build a demonstration reactor, known for the moment as DEMO, which is expected to start contributing energy to the power grid around 2050.

DEMO will form the template for fusion reactors that can be built across the world, in theory enabling fusion to meet the world’s energy needs in conjunction with renewable energy such as wind and solar power.

‘You just have to imagine what the impacts are for mankind as a whole,’ said Simon Webster, the head of the fusion research unit at the European Commission. ‘It’s absolutely phenomenal what this can deliver when you look at the future needs for energy, the growth of world population, and the growing percentage of energy that will need to be provided by electricity generation. Fusion can tick all these boxes.’

However, energy provision is a political, as well as scientific, decision. Final decisions on DEMO are for the future, once ITER has attained its objectives. Whether this project is an international collaboration like ITER, or whether regions will wish to go it alone remains to be seen. China has already pushed ahead in fusion energy and has developed its own tokamak experiment known as EAST, which is situated in the eastern city of Hefei, and is now planning a more advanced fusion energy test reactor.

‘We could do DEMO in the same way (as the planned new Chinese reactor) and say, “OK we are going to build DEMO, we are open to any collaborations with other parties, but this is how we do it, we need a central team with a budget. If other partners want to join, fine”,’ said Professor Tony Donné, the Programme Manager of EUROfusion.

Challenges

One of the biggest problems facing fusion is the issue of exhaust heat – how to extract useful heat for energy generation. At the moment scientists are developing materials which are tough enough to withstand the the high temperatures and neutron bombardment for long periods of time.

Long-term continuous operation of a tokamak is also an issue, but the EUROfusion programme is also studying an alternative configuration known as a stellarator.

Engineers in Germany recently finished building Wendelstein 7-X, the world’s biggest stellarator, which is now being commissioned prior to the start of operation in 2015.

Whether final commercial reactors take the tokamak or the stellarator design, scientists are confident that fusion can become the world’s leading source of power after 2050, and that people will look back to the roadmap drawn up by Europe’s scientists in 2012. ‘They will be able to see a direct trail from what we are setting up now,’ Webster said.

Source: euro-fusion.org

On 9 October 2014 the European Commission invites the fusion community into the heart of the European Quarter, the Solvay Library, to officially launch the European Consortium for the Development of Fusion Energy, EUROfusion for short. The new consortium agreement will substitute the fourteen year-old European Fusion Development Agreement (EFDA), as well as 29 bilateral Association agreements between the Commission and research institutions in 27 countries.

The formation of EUROfusion marks a big step forward for Europe’s quest to develop fusion power as a climate-friendly energy source that will contribute to meet a growing global energy demand. The EUROfusion Consortium enables Europe’s national laboratories to pool their resources even more efficiently – a measure which became necessary to meet the challenge of increasingly complex and large-scale projects such as ITER and DEMO.

The preparation for such a joint fusion programme started in 2012. All EU research laboratories jointly drafted a detailed goal-oriented programme to realise fusion energy by 2050. This programme, known as the ‘Roadmap to the Realisation of Fusion Electricity’ outlines the most efficient path to fusion power. By the end of that year it was endorsed by all parties.
The roadmap has two main aims: Preparing for ITER experiments in order to ensure that Europe makes best possible use of ITER and to develop concepts for a fusion power demonstration plant DEMO. The necessary research towards reaching these aims is carried out by universities and research centres within the current European Framework Programme Horizon 2020. More than before does the programme involve industries in the process of designing components and finding technical solutions.

Through EUROfusion, the European fusion research programme will have direct access to various European experiments that are relevant to fulfil roadmap missions. The world’s largest magnetic fusion experiment, the Joint European Torus (JET) in Culham, UK, will continue to be exploited by EUROfusion until 2018. JET, often nicknamed “Little ITER”, has already been paving the way for ITER and continues to align its scientific programme to ITER needs.

The Solvay library is the ideal venue for the launch of EUROfusion: inaugurated in 1902 its architecture accommodated new ways of academic teaching. The new architecture of EUROfusion strengthens Europe’s leading position in fusion research by integrating a strong central programming.

Source: EFDA.org

The experimental work is described in a paper to be published in the Sept. 24 Physical Review Letters online. A theoretical PRL paper to be published on the same date helps explain why the experimental method worked. The combined work demonstrates the viability of the novel approach.

"We are committed to shaking this [fusion] tree until either we get some good apples or a branch falls down and hits us on the head," said Sandia senior manager Dan Sinars. He expects the project, dubbed MagLIF for magnetized liner inertial fusion, will be "a key piece of Sandia's submission for a July 2015 National Nuclear Security Administration review of the national Inertial Confinement Fusion Program."

Inertial confinement fusion creates nanosecond bursts of neutrons, ideal for creating data to plug into supercomputer codes that test the safety, security and effectiveness of the U.S. nuclear stockpile. The method could be useful as an energy source down the road if the individual fusion pulses can be sequenced like an automobile's cylinders firing.

MagLIF uses a laser to preheat hydrogen fuel, a large magnetic field to squeeze the fuel and a separate magnetic field to keep charged atomic particles from leaving the scene.

It only took the two magnetic fields and the laser, focused on a small amount of fusible material called deuterium (hydrogen with a neutron added to its nucleus), to produce a trillion fusion neutrons (neutrons created by the fusing of atomic nuclei). Had tritium (which carries two neutrons) been included in the fuel, scientific rule-of-thumb says that 100 times more fusion neutrons would have been released. (That is, the actual release of 10 to the 12th neutrons would be upgraded, by the more reactive nature of the fuel, to 10 to the 14th neutrons.)

Still, even with this larger output, to achieve break-even fusion—as much power out of the fuel as placed into it—100 times more neutrons (10 to the 16th) would have to be produced.

The gap is sizable, but the technique is a toddler, with researchers still figuring out the simplest measures: how thick or thin key structural elements of the design should be and the relation between the three key aspects of the approach—the two magnetic fields and the laser.

The first paper, "Experimental Demonstration of Fusion-Relevant Conditions in Magnetized Liner inertial fusion," (MagLIF) by Sandia lead authors Matt Gomez, Steve Slutz and Adam Sefkow, describes a fusion experiment remarkably simple to visualize. The deuterium target atoms are placed within a long thin tube called a liner. A magnetic field from two pancake-shaped (Helmholtz) coils above and below the liner creates an electromagnetic curtain that prevents charged particles, both electrons and ions, from escaping. The extraordinarily powerful magnetic field of Sandia's Z machine then crushes the liner like an athlete crushing a soda can, forcefully shoving atoms in the container into more direct contact. As the crushing begins, a laser beam preheats the deuterium atoms, infusing them with energy to increase their chances of fusing at the end of the implosion. (A nuclear reaction occurs when an atom's core is combined with that of another atom, releasing large amounts of energy from a small amount of source material. That outcome is important in stockpile stewardship and, eventually, in civilian energy production.) Trapped energized particles including fusion-produced alpha particles (two neutrons, two protons) also help maintain the high temperature of the reaction.

"On a future facility, trapped alpha particles would further self-heat the plasma and increase the fusion rate, a process required for break-even fusion or better," said Sefkow.

The actual MagLIF procedure follows this order: The Helmholtz coils are turned on for a few thousandths of a second. Within that relatively large amount of time, a 19-megaAmpere electrical pulse from Z, with its attendant huge magnetic field, fires for about 100 nanoseconds or less than a millionth of a second with a power curve that rises to a peak and then falls in intensity. Just after the 50-nanosecond mark, near the current pulse's peak intensity, the laser, called Z-Beamlet, fires for several nanoseconds, warming the fuel.

According to the paper's authors, the unusual arrangement of using magnetic forces both to collapse the tube and simultaneously insulate the fuel, keeping it hot, means researchers could slow down the process of creating fusion neutrons. What had been a precipitous process using X-rays or lasers to collapse a small unmagnetized sphere at enormous velocities of 300 kilometers per second, can happen at about one-quarter speed at a much more "modest" 70 km/sec. ("Modest" only comparatively; the speed is about six times greater than that needed to put a satellite in orbit.)

The slower pace allows more time for fusible reactions to take place. The more benign implosion also means fewer unwanted materials from the collapsing liner mix into the fusion fuel, which would cool it and prevent fusion from occurring. By analogy, a child walking slowly in the ocean's shallows stirs less mud than a vigorously running child.

Sandia senior scientist Mike Campbell said, "This experiment showed that fusion will still occur if a plasma is heated by slow, rather than rapid, compression. With rapid compression, if you mix materials emitted from the tube's restraining walls into the fuel, the fusion process won't work; also, increased acceleration increases the growth of instabilities. A thicker can [tube] is less likely to be destroyed when contracted, which would dump unwanted material into the deuterium mix, and you also reduce instabilities, so you win twice."

Besides the primary deuterium fusion neutron yields, the team's measurements also found a smaller secondary deuterium-tritium neutron signal, about a hundredfold larger than what would have been expected without magnetization, providing a smoking gun for the existence of extreme magnetic fields.

The question remained whether it was indeed the secondary magnetic field that caused the 100-fold increase in this additional neutron pulse, or some other, still unknown cause. Fortunately, the pulse has a distinct nuclear signature arising from the interaction of tritium nuclei as they slow down and react with the primary deuterium fuel, and that interaction was detected by Sandia sensors.

The secondary magnetic field is the subject of the second, theoretical paper, "Understanding fuel magnetization and mix using secondary nuclear reactions in magneto-inertial fusion." Using simulations, Sandia researchers Paul Schmit, Patrick Knapp, et al confirmed the existence and effect of extreme magnetic fields. Their calculations showed that the tritium nuclei would be encouraged by these magnetic fields to move along tight helical paths. This confinement increased the probability of subsequently fusing with the main deuterium fuel.

"This dramatically increases the probability of fusion," Schmit said. "That it happened validates a critical component of the MagLIF concept as a viable pathway forward for fusion. Our work has helped show that MagLIF experiments are already beginning to explore conditions that will be essential to achieving high yield and/or ignition in the future."

The foundation of Sandia's MagLIF work is based on work led by Slutz. In a 2010 Physics of Plasmas article, Slutz showed that a tube enclosing preheated deuterium and tritium, crushed by the large magnetic fields of the 27-million-ampere Z machine and a secondary magnetic field, would yield slightly more energy than is inserted into it.

A later simulation, published January 2012 in Physical Review Letters by Slutz and Sandia researcher Roger Vesey, showed that a more powerful accelerator generating 60 million amperes or more could reach "high-gain" fusion conditions, where the fusion energy released exceeds by more than 1,000 times the energy supplied to the fuel.

A paper led by Sefkow et al, published July 24, in Physics of Plasmas, further explicated and designed the experiments based on predictions made in Slutz's earlier paper.

But, said Campbell, "there is still a long way to go."

Source: phys.org