PERSPECTIVES ON NUCLEAR-FUSION

Controlled thermonuclear fusion is potentially a major vast new energy source. A reactor based on nuclear fusion would be inherently safe, e nvironmentally friendly, and fuels are cheap, abundant and widely avai lable. The JET tokamak experiment has approached the plasma conditions needed in a thermonuclear reactor based on magnetic confinement conce pts. In single deuterium discharges, breakeven has been achieved and, for the first time with deuterium-tritium fuels, approximately 1.7MW o f fusion power was achieved in a 2s pulse. The total energy release wa s 2MJ. These results were obtained transiently, limited by a high impu rity influx. For long-pulse, high-power operation, plasma dilution has been identified as a major threat to a reactor. Improved impurity con trol in the pumped divertor configuration in a New Phase of JET (1992- 1996) is envisaged. Experimental results support a plasma model based on a single phenomenon and MHD limits.. Together, these are used to de fine the size and operating conditions of a reactor. A Next Step devic e, ITER, would demonstrate the scientific feasibility of ignition unde r reactor conditions and this is discussed within the context of an in ternational collaborative program.