The energy confinement time in stellarators

On the basis of neoclassical transport theory, approximate expressions are proposed for particle and energy fluxes which can be applied over the whole range of collision frequencies of interest for current experimental work and which allow for the contributions of both transit particles and toroidally and locally trapped particles. With the help of these expressions, an evaluation is made of the electron and ion energy confinement times for a number of stellarators (L-2, W-VIIA, Heliotron-E), and it is shown that the calculated confinement times coincide to within an order of magnitude with the experimentally determined values and do not as a rule require the introduction of additional anomalously high losses via the electron channel. Confinement times are calculated for two stellarators still at the design stage (ATF-1 and L-3) and also for a stellarator thermonuclear reactor. It is shown that, in the case of the reactor, the system would not have to be made unreasonably large in order to satisfy the Lawson criterion (N(0)τ E > 10 14 ).