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A tokamak is a machine producing a and Andrei Sakharov . The tokamak is characterized by azimuthal (rotational) symmetry and the use of the plasma current to generate the helical component of the Magnetic Field necessary for stable equilibrium. This can be contrasted to another toroidal magnetic confinement device, the Stellarator , which has a discrete (e.g. five-fold) rotational symmetry and in which all of the confining magnetic fields are produced by external coils with a negligible current flowing through the plasma. HISTORY While research into Nuclear Fusion was conducted after World War II , it was done under Classified programs. It was not until after the 1955 United Nations International Conference On The Peaceful Uses Of Atomic Energy in Geneva that programs were declassified and scientists from different countries allowed to collaborate. In 1968, at the third IAEA International Conference on Plasma Physics and Controlled Nuclear Fusion Research at Novosibirsk , Russian scientists announced that they had achieved electron temperatures of over 1 keV (1 Electron Volt is equal to 11605 Kelvin ) in a tokamak device. This stunned British and American scientists, who were far away from reaching that benchmark. They remained suspicious until tests were done with laser scattering a few years later, confirming the original temperature measurements. Since this performance was far superior to any of their previous devices, most fusion research programs quickly switched to using tokamaks. The tokamak continues to be the most promising device for generating net power from nuclear fusion, reflected in the design of the next generation ITER device. WHY DOUGHNUT SHAPED? The distinctive shape of the fusion reactor is necessary in order to produce a magnetic field with as few irregularities as possible. The Doughnut has a particular topological property that a Sphere (for example) does not have. The problem is referred to as the Hairy Ball Theorem . Imagine a sphere with hair growing out of it. The hair is analogous to the magnetic field lines needed in a fusion reactor. It turns out that it is impossible to comb hair on a sphere so that no hair sticks up. A strand of hair that is standing on end would be equivalent to an instability in the reactor. However, a hairy doughnut can be so combed, and thus adjustments to the magnetic field can be made to correct the irregularities. This allows the magnetic field to better confine the plasma. EXPERIMENTAL TOKAMAKS In operation
Planned SEE ALSO
EXTERNAL LINKS
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