Experimental Modelling of Czochralski Melt Flow with a Slow Crystal Dummy Rotation
This study examines the e ect of slow crystal dummy rotation on three-dimensional oscillatory instability and time-dependent supercritical ow states in a Czochralski melt ow experimental model. To enable further comparison with numerical modelling, the experiments are carried out using a 20 cSt silicone oil as an experimental liquid and in a large diameter crucible, which allows one to work in a narrow temperature interval, so that temperature dependence of all the thermophysical properties of the experimental liquid can be neglected. The measurements con rm, partially qualitatively and partially quantitatively, earlier numerical predictions on destabilization ofthe Czochralski convective ow by a slow rotation. A simple power dependence of ow oscillations frequency on the Grashof and rotational Reynolds numbers that ts all the experimental runs was found.
Experimental and computational study of flow instabilities in a model of Czochralski growth
The results of experimental modeling of Czochralski flow of large-Prandtl-number oxide melts are reported. An instability mechanism resulting in cold plumes detaching from the cold crystal and then descending towards the crucible bottom is observed. With the increase of the temperature difference or crystal rotation the baroclinic instability mechanism, characterized by three-dimensional oscillations of a cold jet descending along the symmetry axis, becomes dominant. The experiments are carried out for different silicone oils characterized by different Prandtl numbers and for varying crystal/crucible radii ratio. Results of computational modeling results qualitatively agree with the experimental observations. Possible reasons for the quantitative disagreement are discussed.
Microwave source with enhanced radiation power based on orbitron MASERs
We have proposed the design of high power microwave source in a vacuum tube based on the theory of negative mass instability. The proposed source does not operate based on a slow-wave structure but instead makes use of accelerated charged particles. In our structure, an electron emitter injects the charged particles into to the cavity. Emitted particles move around the anode, which leads to electron acceleration and emission of electromagnetic waves with a specific frequency. In this paper, we have enhanced the output power and frequency of microwave source by variation of particles initial energy and the number of anodes incorporating their specific arrangement and applied voltages. Working at room temperature, compactness, wide bandwidth, and tunability of output frequency are among the advantages of the proposed source.