[en] The status of knowledge of tokamak discharges with a bundle divertor is described, in particular concerning the effectiveness of a bundle divertor for compositional control and exhaust, first for tokamak experiments, then for the Next European Torus (NET). Magnetic geometry, results from the DITE tokamak experiment, modelling of bundle divertors; assessment of divertor performance, extrapolation from the DITE experiment and from modelling to NET, and comments on reactor bundle divertor designs, are all discussed. (U.K.)

[en] Models of the edge region of a toroidal plasma are described and developed, the eventual aim being to be able to link plasma models of one-dimensional parallel flow to a radial transport code and ultimately to an overall model of the NET system. It is concluded that parallel flow requires a two-fluid description, evaluated numerically or analytically. The full numerical approach, using program ZEPHYR, which is fully documented, is used for many test cases of the parallel flow model. (author)

[en] The second electron emission coefficient of various materials, namely titanium, molybdenum, tungsten and sapphire, has been calculated for a Maxwellian energy distribution from data for a normally incident monoenergetic beam of primary electrons. The most significant difference from the monoenergetic case occurs at low energies. In addition the influence of the incident angle of the electrons is discussed. (author)

[en] Using a very simple, single-fluid model, with one-dimensional transport parallel to the field, the cause of asymmetry which leads to current flow in a scrape-off layer is analysed. Plasma and pre-sheath potentials at two sheaths at the ends of a flux tube in the scrape-off layer are calculated for a specific example, typical of JET with a single-null X-point configuration

[en] A floating double probe has been used to measure time-resolved profiles of electron density and temperature in the boundary layer of DITE. The results compare favourably with profiles from other diagnostics at smaller radii. The radial profiles outside the limiter have been used to derive upper bounds on the power conducted to the limiters in diverted discharges. The density profiles are compared with calculated profiles assuming a Bohm-like diffusion coefficient. (orig.)

[en] Some consequences of the release of electrons at a divertor target have been considered with particular reference to the collisionless exhaust of a D-T reactor. These electrons share the energy of the thermonuclear α particles and thereby cool the divertor plasma and lower the sheath potential at the target. A limit is set by space charge saturation in the sheath and some target materials have sufficiently large yields of secondary electrons for saturation to occur. Even so, the sheath potential will be in excess of the thresholds for unipolar arcing. (Auth.)

[en] This report presents a compilation of papers dealing with reactor exhaust which were produced as part of the TIGER Tokamak Installation for Generating Electricity study at Culham. The papers are entitled: (1) Exhaust impurity control and refuelling. (2) Consideration of the physical problems of a self-consistent exhaust and divertor system for a long burn Tokamak. (3) Possible bundle divertors for INTOR and TIGER. (4) Consideration of various magnetic divertor configurations for INTOR and TIGER. (5) A appraisal of divertor experiments. (6) Hybrid divertors on INTOR. (7) Refuelling and the scrape-off layer of INTOR. (8) Simple modelling of the scrape-off layer. (9) Power flow in the scrape-off layer. (10) A model of particle transport within the scrape-off plasma and divertor. (11) Controlled recirculation of exhaust gas from the divertor into the scrape-off plasma. (U.K.)

[en] We describe the development of a one-dimensional model for the flow of plasma in the scrape-off layer and divertor of a reactor-scale tokamak. Some analytic results and preliminary numerical results are presented. (author)

[en] The aim of this paper is to present and interpret measurements of fluctuation level made in the boundary layer of DITE using a Langmuir double probe. Estimates of diffusion coefficient, based on these results are comparable to values determined from density scale lengths in this region. It is shown that the fluctuations are strongest in regions where the parallel flow velocity in the boundary plasma is likely to be near-sonic and that they are weaker elsewhere. It is known that near-sonic and transonic fluid-flows are highly susceptible to instabilities caused by very small perturbations of the parallel flow and that the magnitude of these 'transonic flow instabilities' increases as the sonic speed is approached. Possible sources of small perturbations are considered, which, coupled with the variation in Mach number, support the suggestion by Stangeby that the fluctuations observed are transonic flow instabilities. (orig.)

[en] Properties of the single-null divertor of INTOR are considered in relationship to the transport of plasma particles and energy in the toroidal scrape-off region and the poloidal divertor chamber. (orig./AH)