FUSION - POWER FOR THE 21st CENTURY.

For the purposes of releasing energy in a fusion reactor the reaction between deuterium and tritium has the highest cross-section and is thus easiest to achieve. The probability of this reaction occurring is greatest when the two nuclei collide with a relative energy of the order of 100 keV and a random collection of such particles has a temperature (T) equivalent to 10**9 **0C and is referred to as a plasma. The requirement to obtain more energy from the nuclear reactions in the plasma than is invested in heating it and maintaining its temperature can be fulfilled if the product of the plasma density (n) and its energy containment time (T) exceeds a minimum value, which for the D-T reaction is 2. 10**2**0 s. m** minus **3. A similar requirement is obtained if the plasma temperature is to be self-sustained as a result of the nuclear reactions. The tokamak is a toroidal magnetic confinement system in which a strong toroidal magnetic field generated by external windings and a weaker poloidal magnetic field generated by a toroidal current flowing in the plasma give a toroidal confining field with a slight twist. The plasma current also heats the plasma by ohmic dissipation. Measured values of nT are still two orders of magnitude less than required for a reactor and temperatures one order of magnitude less. A study group of the International Atomic Energy Agency, consisting of 12 or 16 representatives from Europe, Japan, USA and USSR, hope to report in one year on the possibilities of a large fusion device known as INTOR (International Tokamak Reactor) to operate in the late 1980's or early 1990's.