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Improved tokamak concepts for JET and the future

The economic viability of Tokamak fusion reactors would be greatly improved if the capital cost were significantly reduced and continuous operation were possible. Designs which realise these goals rely on reduction by a factor 2-3 in plasma current, from the 25 MA needed for a good ignition margin in ITER. A substantial proportion of bootstrap current is needed, in order to keep the recirculating power to a small proportion of the fusion output. These requirements define an operating point which has to be at large beta p ( approximately 2.5-3) and high beta t ( beta N approximately 3-5). Also the energy confinement must be well above H-mode. Steps have already been taken in this direction at JET and a programme has evolved which emphasises coherent development of steady state plasmas. JET has large heating and current drive systems, long pulse capability, He neutral beam injection for ash transport studies and the recently installed, pumped divertor. The results which have already been obtained and the future programme are described. Attention is drawn to the potential application of concept improvement techniques to JET's high performance plasmas so that the fusion yield and Q may be improved.