Impurities in Tokamaks: Sources, Effects and Control (Report on the IAEA Technical Committee Meeting, Alushta, 1979)

The IAEA Technical Committee on Impurities in Tokamaks met at Alushta (Ukrainian SSR) from 8 to 12 October 1979. It discussed the present status of knowledge on the behaviour of impurities in tokamaks – their sources and dynamics, and the methods of controlling them. The meeting was convened at the initiative of the IAEA and organized by the Kharkov Physico-Technical Institute. At Alushta, 23 participants from seven countries (eight from USA, seven from the Federal Republic of Germany, three from France, two from Great Britain and one each from Hungary, the Netherlands and Japan) came together with 14 participants from the USSR. In more than 30 papers and during the extensive discussions which followed the presentations practically all the main aspects of the impurity problem were considered. As a result of the meeting, it became clear that in the last five years substantial advances had been made towards obtaining, in tokamaks, a sufficiently pure plasma with Zeff close to unity. This has been achieved by using new methods of purifying the discharge chamber walls, titanium gettering, graphite limiters and programmed filling of gas. Active methods of impurity control – with divertors and asymmetric injection of neutral hydrogen – were also found to be successful. The principal conclusions arrived at by the participants are reviewed below.