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Near breakeven conditions have been attained in the JET tokamak, with beryllium as the first wall material. A fusion triple product of 8 to 9 x 1.0 E20 s.keV/m3 has been reached, within a factor of 8 of that required in a fusion reactor. However, this has only been achieved transiently. At high heating powers, an influx of impurities still limits the achievement of better performance and steady state operation. In parallel, an improved quantitative understanding of fusion plasmas has emerged from the development of a particular plasma model. Good quantitative agreement is obtained between the model and JET data. The main predictions are also consistent with statistical scaling laws. With such a model, it is possible to define the parameters and operating conditions of a DEMO, including impurity levels. A divertor concept must be developed further to ensure impurity control, before a DEMO can be constructed. A new phase for JET is planned in which an axisymmetric pumped divertor configuration will be used to address the problems of impurity control, plasma fuelling and helium ash exhaust. A single Next Step facility (ITER) is a high risk strategy in terms of physics, technology and management, since it does not provide a sufficiently sound foundation for a DEMO. A Next Step programme is proposed, which could comprise several complementary facilities, each optimised with respect to specific clear objectives. In a minimum programme, there could be two Next Step tokamaks, and a materials test facility.

Additional information

Authors: REBUT P-H, JET Joint Undertaking, Abingdon, Oxon. (GB);WATKINS M L, JET Joint Undertaking, Abingdon, Oxon. (GB);GAMBIER D J, JET Joint Undertaking, Abingdon, Oxon. (GB);BOUCHER D, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(90)75 EN (1990) 29 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199110574 / Last updated on: 1994-12-02
Original language: en
Available languages: en