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With the advent of the new large tokamaks such as JET, JT-60, TFTR, important advances in magnetic confinement have been made. A number of small and medium sized tokamaks have also come into operation, each addressing specific problems which remain for the future development of the system. The tokamak has moved from success to success over a period of some 25 years and this has been achieved without any control of the current distribution. Many research workers now believe that the final step can be achieved by providing that control with the application of non-inductive current drive. Lower hybrid current drive has now been used very effectively and efficiently on JT-60 and electron cyclotron resonance heating current drive has been demonstrated on smaller devices. The control of the current distribution has led to the stabilisation of the internal sawtooth oscillation and m=2 activity. Sawtooth control has led to impressive rises in central electron temperature. A key feature of recent experiments has been the possible demonstration of the existence of the bootstrap current which is a neoclassical prediction for a toroidal device. Ion and electron cyclotron resonance heating together with neutral beam heating have been highly successful, however in most cases they lead to some degradation in energy confinement time. This degradation can be avoided with the so called H-mode which occurs in magnetic configurations with a separatrix. The best nTtau product for magnetic fusion has been achieved on the JET device with an H-mode. An alternative method of achieving enhanced confinement has been established with the super shots on TFTR. Density and beta limits still pose important restrictions on tokamaks. Shaping and profile control should improve the beta limit. Pellet refueling has also proven to be a highly satisfactory technique for improving confinement and decreasing the impurity concentration. It now seems quite likely that today's tritium compatible tokamaks will demonstrate substantial alpha particle heating within the next few years.

Additional information

Bibliographic Reference: REPORT CLM-P828, 1987, AVAILABILITY: UKAEA, ABINGDON, UK
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