History of the approach to ignition

The origin of the energy of the stars as being due to the fusion of light n uclei was identified by Edington in 1920. In the late 1940s, work started, aimed at creating suitable conditions in the laboratory to develop a major new energy source for the world. The two radically different approaches dep end either on the inertia of a small dense hot pellet or on the use of magn etic fields to control and contain the motion of charged particles. This pa per concentrates largely on the latter 'magnetic confinement' history leavi ng 'inertial confinement' to other contributors. Early work saw the inventi on of a wide variety of magnetic-field geometries for the confinement of ho t ionized gases (plasmas). By a process of natural selection, this has been almost entirely reduced to so-called 'closed toroidal systems', such as th e stellarator, tokamak and reversed-field pinch. Effort has been concentrat ed on the tokamak, culminating in the present position where 'breakeven' ha s been achieved in large machines. An improvement by a further factor of fi ve to ten in the key triple-product parameter (n tau T) is needed to reach the ignition point where the reaction becomes self-sustaining. New machines designed to achieve this, and in one case (International Thermonuclear Exp erimental Reactor) to demonstrate the technical feasibility of an ultimate power-generating system, are under consideration. A course of action in thi s direction is recommended.