Inside a tokamak
(a) Tore Supra has been fitted with an actively cooled toroidal pump limiter, which will be an essential technology for an eventual fusion reactor. These photos of the limiter were taken with a CCD camera during a plasma lasting four minutes, which was heated by 3 MW of radio-frequency power. There is no difference between these photos, which shows that the limiter - which is in direct contact with the plasma - remains at a steady temperature. The bright area corresponds to a temperature of 320 °C. (b) The physical and technological events that are encountered during a plasma discharge have characteristic timescales. A short plasma duration of tens of seconds is long enough for studying the MHD instabilities that have a strong influence on the fusion rate. These include kink instabilities that distort the magnetic surfaces and the plasma boundary. Particle and energy confinement can also be studied, but no existing fusion experiment can address integrated physical and technological issues.