TOKAMAK
A tokamak is a machine producing a toroidal magnetic field for confining a plasma. It is one of several types of magnetic confinement devices and the most researched candidate for producing fusion energy.
One of the main problems of fusion is that ions and electrons in the centre of a fusion plasma are at very high temperatures, and have correspondingly large velocities. In order to maintain the fusion process, particles from the hot plasma must be confined in the central region, or the plasma will rapidly cool.
In a tokamak, confinement is obtained by the Lorentz force (synonymous with magnetic force). The magnetic lines fill a vacuum chamber where ions and electrons move (yellow in the picture below).
Tokamak magnetic field is composed by two elements:
- magnetic lines generated by toroidal magnets (black arrows in the picture below)
- magnetic lines generated by poloidal magnets (blue arrows in the picture below)
The tokamak toroidal magnets, feeded by a constant electric current, generate magnetic lines which run parallel to the axis of the toroid : the field is stronger towards the center, causing the plasma to tend towards the outer wall. However, another magnetic field generated by a current going through some poloidal magnets combines with the toroidal magnets' field to create magnetic lines that spiral around the torus . This spiralling counteracts the drifting effect on the plasma because of the strong inner field, and effectively traps the plasma. Therefore, these charged particles are confined by the strong magnetism and are forced to follow helical paths along the field lines without impinging on the chamber walls.
The term Tokamak is a transliteration of the Russian words: "toroidal'naya kamera s magnitnymi katushkami" — toroidal chamber with magnetic coils (Tochamac). It was invented in the 1950s by Soviet physicists Igor Yevgenyevich Tamm and Andrei Sakharov (who were in turn inspired by an original idea of Oleg Lavrentyev).
Experimental research of tokamak systems started in 1956 in Kurchatov Institute, Moscow by a group of Soviet scientists led by Lev Artsimovich. The group constructed the first tokamaks,conducting in 1968 the first ever quasistationary thermonuclear fusion reaction.
In 1968, at the third IAEA International Conference on Plasma Physics and Controlled Nuclear Fusion Research at Novosibirsk, Soviet scientists announced that they had achieved electron temperatures of over 1.000.000 K in a tokamak device. This stunned British and American scientists, who were far away from reaching that benchmark.
Since then, the tokamak continues to be the most promising device for generating net power from nuclear fusion, reflected in the design of the next generation devices.
(informazioni prese da WIKIPEDIA)
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