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The shape of a plume conduit produced by melting solid paraffin block above a local heat source was studied experimentally as a function of the relative thermal power of the plume Ka = N/N1, where N1 is the power of the plume source and N1 is the power corresponding to the amount of heat transferred by conduction through the plume conduit to the surrounding solid paraffin block. The limiting power of the plume source at which the plume erupts at the Earth’s surface (Nlim1 = (1.35–1.60) × 1010 W) and the power at which the mushroom-shaped plume head formed at the base of the refractory layer (Nlim2 = (1.78–1.90) × 1010 W) with no horizontal mantle flow were determined. The dependence of the diameter of the base of the plume on the Ka number was established. The Ka value and the diameter of the plume base were determined for the Hawaiian and Iceland plumes, for the plume responsible for the formation of the Tunguska syneclise and for the McKenzie and Central Atlantic continental plateau-basalt provinces and for the Ontong Java and Manihiki oceanic lava plateaus.

532.5+536.25+548.5In model experiments, the layer of melt bounded by the crystallization front and the heater for heatin 9 the diaphragm in a growing furnace is shown to determine crystal growth by the Stockbarger method under conditions of induced convection and also to control the crystallization process. The free volume of the melt exerts no effect on its hydrodynamic and thermal structures. Optimum values of the exposure time are estimated for constant mazimum and minimum velocities of modulated rotation of the growing ampoule.In studying the effect of the temperature field in a growing furnace on the optical quality of crystals grown by the Stockbarger method, Godovikov et al. [1] noted that the determining factors are the position of the crystallization front in the growing furnace and the perturbation of the thermal field in close proximity of this front. It is clear that studying the effect of one parameter is possible only if the other controlled parameters that determine the crystallization conditions are constant. As in the classical Stockbarger method (see Fig. 1), we formed a temperature field in a growing furnace by three heaters: an upper heater, a lower heater, and a middle heater (a heater for heating the diaphragm).We studied three positions of the crystallization front relative to the annular heater for the diaphragm and its effect on the optical quality of proustite single crystals (AgnAsS3, a nonlinear-optics material with Tmelt = 485~Single crystals of high optical quality were grown only if the crystallization front was positioned below the diaphragm, although Stepanov and Vasil'eva [2] noted that it is impossible to obtain high-quality single crystals under similar conditions. Meanwhile the most positive effect in creating large single crystals for optoelectronics by the Stockbarger method is attained with the use of forced stirring of the melt by the method of modulated rotation of the growing container [3]. Stirring is caused by the presence of intense flows in the melt. These flows are directed radially from the cylinder's generatrix to the axis of rotation if the velocity of rotation of the ampoule slows down and from the axis to the cylinder's generatrix upon acceleration [4] (Fig. 2a and b).In experiments on physical modeling of the hydrodynamics and heat and mass transfer in the melt in growing single crystals by the ACRT, we considered the case where the thickness of the melt layer was equal to or slightly exceeded the distance from the crystallization front to the annular heater for heating the diaphragm [5]. Since in the process of growing real crystals by the Stockbarger method (especially at its initial stage), a melt layer positioned above the level of the middle heater always exists, it is important to know its effect on the general hydrodynamic and thermal structure of the melt. Under real conditions, this layer has a constant temperature along the axis of the growing furnace already at a small distance above the diaphragm.In the present paper, we model the thermal struc...

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