JET and the Prospect for Nuclear Fusion

Abstract

This paper describes the Joint European Torus (JET) device which was built as a European collaboration effort, with the aim of testing the scientific feasibility of producing controlled thermonuclear reactions between light nuclei with a net yield of energy.JET is the largest magnetic confinement machine in the world both in physical size and in the magnitude of the plasma current (5 × 106 Amperes). The machine came into operation in mid-1983 and has followed the first stages of a planned evolution, in which the performance is progressively increased mainly by adding more heating power and which will culminate in eventual operation in a deuterium-tritium mixture. This will permit study of the plasma performance when there is a substantial power input from the α-particle fusion products. So far operating in deuterium gas with 8 MW of additional heating by neutral beams, a peak ion temperature of 12 keV has been obtained with a corresponding fusion product (density × confinement time) of 8 × 1018 m-3 s. If the same conditions were to be achieved in a deuterium-tritium mixture, then the ratio of thermonuclear power output to the heating power input, Q, would be ∼ 0.1. It is expected that following further technical improvements to JET, "scientific breakthrough" (namely Q = 1) will be achieved.The next step after JET will be to study a burning or ignited plasma in which no power input is required because energy losses are balanced by α-particle heating. The requirements for such an experiment will become increasingly clear as more data is obtained from JET. At present it seems likely that a larger apparatus will be needed with a plasma current capability of 12-15 MA. These requirements for the thermonuclear furnace remain broadly consistent with the known technological constraints on an eventual power reactor.