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[en] Some problems relating to cryopumps for selective pumping of impurity gases in the ''Globus'' tokamak are considered. The dependence on geometry of the pumping speed of the system was determined in molecular regime and taking into account the influence of unpumped hydrogen. The values of the heat load of the cryopumping systems are estimated under different operating conditions. Several types of cooling system are proposed. (Author)
[en] Our study demonstrates a remarkable flexibility of advanced divertor configurations created with the remote poloidal field coils. The emphasis here is on the configurations with three poloidal field nulls in the divertor area. We are seeking the structures where all three nulls lie on the same separatrix, thereby creating two zones of a very strong flux expansion, as envisaged in the concept of Takase's cusp divertor. It turns out that the set of remote coils can produce a cusp divertor, with additional advantages of: (i) a large stand-off distance between the divertor and the coils and (ii) a thorough control that these coils exert over the fine features of the configuration. In reference to these additional favourable properties acquired by the cusp divertor, the resulting configuration could be called 'a super-cusp'. General geometrical features of the three-null configurations produced by remote coils are described. Furthermore, issues on the way to practical applications include the need for a more sophisticated control system and possible constraints related to excessively high currents in the divertor coils
[en] We measured iron emission from the National Spherical Tokamak Experiment. We focused our attention on several band pass regions of the Solar Dynamics Observatory's Atmospheric Imaging Assembly. We found that all significant iron emission in the 171, 193 and 211 Å band pass regions are accounted for by the CHIANTI atomic database, although some strong emission lines of carbon are present that may complicate interpretation of solar data if not taken into account. (paper)
[en] In this study, observations of divertor plasma detachment in tokamaks are reviewed. Plasma detachment is characterized in terms of transport and dissipation of power, momentum and particle flux along the open field lines from the midplane to the divertor. Asymmetries in detachment onset and other characteristics between the inboard and outboard divertor plasmas is found to be primarily driven by plasma x drifts. The effect of divertor plate geometry and magnetic configuration on divertor detachment is summarized. Control of divertor detachment has progressed with a development of a number of diagnostics to characterize the detached state in real-time. Finally the compatibility of detached divertor operation with high performance core plasmas is examined.
[en] Characteristics of tokamak current quenches are an important issue for the determination of electro-magnetic forces that act on the in-vessel components and vacuum vessel during major disruptions. The characteristics of current quenches in spontaneous disruptions in the J-TEXT tokamak have been investigated. It is shown that the waveforms for the fastest current quenches are more accurately fitted by linear current decays than exponential, although neither is a good fit in many slower cases. The minimum current quench time is about 2.4 ms for the J-TEXT tokamak. The maximum instantaneous current quench rate is more than seven times the average current quench rate in J-TEXT. (paper)
[en] Geodesic acoustic modes (GAMs) in a tokamak excited by, for example, energetic particles can create a direct energy channel from energetic population to turbulence. In this paper, the ability of GAMs to further convert their energy into large scale motion such as zonal flows is investigated. The simplest case of GAMs, neglecting the effects of normal curvature, Alfven wave effect and drift effects, is considered. It is shown that such GAMs are stable with respect to generation of zonal flows.