The burn condition for D-T plasmas is derived in a form which accounts for the stationary helium concentration determined by the coupling of the fusion power and helium production. The ratio of the global alpha particle confinement time r a to the energy confinement time T E is taken as a quantity characterizing the prevailing confinement and exhaust regime. For an ignited and stationary burning D-T plasma this ratio needs to remain sufficiently below 15 or below 10 for typical impurity concentrations. This poses a lower limit on the required helium exhaust efficiency and indicates that operational regimes are needed where the particle confinement time does not diverge too far from the energy confinement time. Applied to the D-3 He fusion reaction, the analysis leads to even more stringent limits on the ratio T'JT E , which must be smaller by a factor of three to four compared to the D-T case. It is found that, for any given temperature (and for otherwise equal exhaust and recycling conditions), in general burning can be achieved at two different values of the fusion parameter n T T E and ash concentration.

Helium, as the ash of burning D-T plasma, is an unavoidable impurity component necessarily present already in near future tokamak experiments with significant alpha particle heating. Its efficient removal from the burning zone of a D-T fusion reactor (or lack thereof) will play a key role in the path towards achievement of economic fusion power production. A survey is given of the issues related to this question. Since there is as yet no experimental experience with thermonuclear plasmas significantly heated by fusion products, this review is based on results from simulation experiments of helium injection into hydrogen or deuterium tokamak plasmas, and from numerical transport code work. Both kinds of results are discussed with reference to handy ignition criteria obtained for steady D-T burning, which have been reformulated in terms relevant for the ash removal problem.

The 11th European Conference on Controlled Fusion and Plasma Physics was held from 5 to 9 September 1983 in the Kármán Auditorium of the University of Aachen, FRG. The Conference, organized by the Nuclear Research Centre Jülich, was attended by nearly 500 participants from over 30 countries, among them guest delegations from several non-European countries. The scientific material was presented in 24 invited papers, 36 short oral contributions, and about 250 posters spread over five poster sessions.The present review is necessarily limited and cannot give proper credit to each work presented at the Conference. According to the Conference programme, this report is divided into ten sections with emphasis on magnetic confinement and related problems and topics.

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However, the generally predicted rapid growth of the m=I internal kink for the case of q(0) about 0.6 has also been observed (Fig. 6). After more than 0.5 sec during which the current distribution has shown a fairly stationary behaviour with only small density sawteeth (Fig.7), a large m=I mode develops, and the observed negative voltage spike indicates a large poloidal flux change. Eventually, this leads to a termination of the discharge. These phenomena would be difficult to understand with the assumption of q(0) near I. Conditions under which the resistive m=I mode may be marginally stable are not known theoretically for q on axis significantly less than I and are now being investigated / 2 2 / .