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| Stare chamber |
It would provide humankind with near limitless energy, ending dependence on fossil fuels for generating electricity.
US Government physicists have backed plans to create 'a star in a jar' - replicating on Earth the way the sun and stars create energy through fusion.
Physicists at the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) revealed their plan for a next generation fusion device in a paper published in the journal Nuclear Fusion.
The central stack of the reactor being lowered into place (left)
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| Antigravity chamber |
Physicists at the U.S. Department of Energy's Princeton Plasma Physics Laboratory revealed their plan for a next generation fusion device in a paper published in the journal Nuclear Fusion. Pictured, researchers inside the centre stack of the $94-million upgrade of the National Spherical Torus Experiment-Upgrade, which began operating last year.
'We are opening up new options for future plants,' said lead author Jonathan Menard, program director for the recently completed National Spherical Torus Experiment-Upgrade (NSTX-U) at PPPL.
The $94-million upgrade of the NSTX, financed by the U.S. Department of Energy's Office of Science, began operating last year. Spherical tokamaks are compact devices that are shaped like cored apples, compared with the bulkier doughnut-like shape of conventional tokamaks.
The plants already exists in experimental form - the compact spherical tokamaks at PPPL and Culham, England. These tokamaks, or fusion reactors, could provide the design for possible next steps in fusion energy - a Fusion Nuclear Science Facility (FNSF) that would develop reactor components and also produce electricity as a pilot plant for a commercial fusion power station.
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| How to guide plasma |
How it works: Fusion involves placing hydrogen atoms under high heat and pressure until they fuse into helium atoms.
Fusion involves placing hydrogen atoms under high heat and pressure until they fuse into helium atoms. When deuterium and tritium nuclei - which can be found in hydrogen - fuse, they form a helium nucleus, a neutron and a lot of energy. This is down by heating the fuel to temperatures in excess of 150 million°C, forming a hot plasma.
Strong magnetic fields are used to keep the plasma away from the walls so that it doesn't cool down and lost it energy potential.
These are produced by superconducting coils surrounding the vessel, and by an electrical current driven through the plasma. For energy production, plasma has to be confined for a sufficiently long period for fusion to occur.
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| Increase power |
The increased power of the upgraded PPPL machine and the soon-to-be completed MAST Upgrade device moves them closer to commercial fusion plants, the researchers say.
The NSTX-U and MAST facilities 'will push the physics frontier, expand our knowledge of high temperature plasmas, and, if successful, lay the scientific foundation for fusion development paths based on more compact designs,' said PPPL Director Stewart Prager.
However, the devices face a number of physics challenges.
For example, they must control the turbulence that arises when superhot plasma particles are subjected to powerful electromagnetic fields. They must also carefully control how the plasma particles interact with the surrounding walls to avoid possible disruptions that can halt fusion reactions if the plasma becomes too dense or impure.
Researchers at PPPL, Culham, and elsewhere are looking at ways of solving these challenges for the next generation of fusion devices.
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| Looks and is scary |
This unique capability points the way to a possible next generation of fusion experiments to complement ITER, the international tokamak that 35 nations including the United States are building in France to demonstrate the feasibility of fusion power.
ITER is a doughnut-shaped tokamak that will be largest in the world when completed within the next decade.
Physicists at the U.S. Department of Energy's Princeton Plasma Physics Laboratory revealed their plan for a next generation fusion device in a paper published in the journal Nuclear Fusion.
Pictured, a test cell for the $94m National Spherical Torus Experiment-Upgrade with its tokamak in the centre.
WHAT IS ITER?
The International Thermonuclear Experimental Reactor (Iter) will be the world's largest tokamak nuclear fusion reactor when it's complete in 2019. 35 nations including the United States are building it in France to demonstrate the feasibility of fusion power.
But its construction is proving a challenge. A team of engineers in France is currently grappling with building the massive device, which has magnets that weigh as much as a Boeing 747.
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| Thermonuclear Experimental Reactor |
'The main reason we research spherical tokamaks is to find a way to produce fusion at much less cost than conventional tokamaks require,' said Ian Chapman, the newly appointed chief executive of the United Kingdom Atomic Energy Authority and leader of the UK's magnetic confinement fusion research programme at the Culham Science Centre. A key issue is the size of the hole in the center of the tokamak that holds and shapes the plasma. In spherical tokamaks, this hole can be half the size of the hole in conventional tokamaks, enabling control of the plasma with relatively low magnetic fields. The smaller hole could be compatible with a blanket system for the FNSF that would breed tritium, a rare isotope - or form - of hydrogen.
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| Thermonuclear |
Existing experiments have used bulkier doughnut-like shapes, such as the world's largest 'Stellarator' fusion reactor. Dubbed Wendelstein 7-X (W7-X), the reactor is designed to contain super-hot plasma for more than 30 minutes at a time Tritium will fuse with deuterium, another isotope of hydrogen, to produce fusion reactions in next-step tokamaks. For pilot plants, the authors call for superconducting magnets to replace the primary copper magnets in the FNSF. Superconducting magnets can be operated far more efficiently than copper magnets but require thicker shielding. However, recent advances in high-temperature superconductors could lead to much thinner superconducting magnets that would require less space and reduce considerably the size and cost of the machine. Included in the paper is a description of a device called a 'neutral beam injector' that will start and sustain plasma current without relying on a heating coil in the center of the tokamak. Such a coil is not suitable for continuous long-term operation. The neutral beam injector will pump fast-moving neutral atoms into the plasma and will help optimize the magnetic field that confines and controls the superhot gas.
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| As hot as the sun |
Pictured The first plasma in Wendelstein 7-X. It consisted of helium and reached a temperature of about one million degrees Celsius Earlier this year scientists successfully switched on the world's largest 'Stellarator' fusion reactor. Dubbed Wendelstein 7-X (W7-X), the reactor is designed to contain super-hot plasma for more than 30 minutes at a time. This week, the reactor produced a special super-hot gas for a tenth of a second. Scientists hope that, if it can work for longer, it could eventually lead to limitless supplies of clean and cheap energy. The reactor produced a helium plasma which reached a temperature of one million°C.
Researchers claim the unusual design, which is housed in a huge lab in Greifswald, Germany, could finally help make fusion power a reality 'We're very satisfied', concludes Dr Hans-Stephan Bosch, whose division is responsible for the operation of the Wendelstein 7-X, at the end of the first day of experimentation. 'Everything went according to plan.' The next task will be to extend the duration of the plasma discharges and to investigate the best method of producing and heating helium plasmas using microwaves. Researchers claim its unusual design, which is housed in a huge lab in Greifswald, Germany, could finally help make fusion power a reality. Containing super-hot plasma for long periods has been the Holy Grail for reactor designs, and could help scientists provide an inexhaustible source of power. Fusion reactors, such as the W7-X, work by using two kinds of hydrogen atoms — deuterium and tritium — and injecting that gas into a containment vessel.
Pictured is the initial test of the system. The image shows how the fluorescent rod makes closed, nested magnetic surfaces visible Scientist then add energy that removes the electrons from their host atoms, forming what is described as an ion plasma, which releases huge amounts of energy. Strong magnetic fields are used to keep the plasma away from the walls; these are produced by superconducting coils surrounding the vessel, and by an electrical current driven through the plasma. The most common design for a reactor is something known as a Tokamak, which is a hollow metal chamber in the shape of a donut. The fuel is heated to temperatures in excess of 150 million°C, forming a hot plasma. While the Tokamak design is ideal for containing this plasma, it poses some safety risks, for instance, if the current fails or there's a magnetic disruption.
In stellarators, plasma is contained by external magnetic coils which create twisted field lines around the inside of the vacuum chamber These disruptions can unleash magnetic forces powerful enough to damage the reactor. Scientists at the Max Planck Institute say the W7-X is a more practical option and can overcome the safety problems of a Tokamak reactor, according to an in-depth report in Science. 'Tokamak people are waiting to see what happens. There's an excitement around the world about W7-X,' engineer David Anderson of the University of Wisconsin, Madison told Science. In tokamaks, two sets of magnets are used to contain the plasma; an external set surrounding the vacuum chamber and an internal transformer that drives current in the plasma.
This causes the magnetic field to be stronger in the centre than it is on the outer side. As a result, plasma contained in a tokamak can moves to the outer walls where it then collapses. In stellarators, plasma is contained by external magnetic coils which create twisted field lines around the inside of the vacuum chamber, according to Science.
The photograph on the left combines the tracer of an electron beam on its multiple circulation along a field line through the machine. On the right is one of the interior components of the W7-X being made As such, it overcomes can continuously hold the plasma away from the walls of the device. Its key component is a ring 50 superconducting magnetic coils approximately 3.5 metres in height. In total the device is 16-meters-wide. The stellarator design was first thought up in 1951 by Lyman Spitzer working at Princeton University. But at the time, it was thought to be too complex for the constraints of materials available in the middle of the 20th Century. Now using supercomputers and new materials, researchers have finally made Spitzer's vision a reality.
While the Tokamak design is ideal for containing this plasma, it poses some safety risks, for instance, if the current fails or there's a magnetic disruption 'We all know the trend of global development, the hunger for energy of emerging economies and emerging countries,' said Professor Johanna Wanka, Federal Minister for Education and Research. 'So when we talk about energy, we need research that keeps all options open. And one of these options is nuclear fusion. 'Wendelstein 7-X is an important step forward allowing us to better evaluate the 'fusion option.' The machine took 1.1 million hours to assemble, using what has been described as one of the world's most complex engineering models. Testing of the magnetic field in the Wendelstein 7-X fusion device was completed in June – much sooner than expected. The test revealed that the magnetic cage for the fusion plasma, which has a temperature of many million degrees, was working as scientists predicted. If the machine works for longer periods of time, scientists believe it could herald a change in the direction for fusion power.
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