Title: Feedback Control of Morphological Instabilities
Speaker: Alexander A. Nepomnyashchy
Speaker Info: Technion
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The morphological instability of a crystal growth is one of the most important types of crystal growth instabilities. The non-uniformity of the crystal composition caused by the morphological instability greatly reduces the crystal quality. In some cases, the development of the morphological instability is not saturated due to the nonlinear factors and leads to the formation of deep cells and dendrites.Date: Friday, February 14, 2003
The present talk is devoted to the problem of the feedback control of morphological instabilities in the course of the directional solidification. The possibility of a feedback control is studied for both monotonic and oscillatory instabilities. Two ways of the feedback control are considered: (1) a local control by means of external heating within the melt in the vicinity of the melt/crystal interface; (2) a global control by adjusting the applied temperature gradient and the pulling speed. A special attention is paid to the case of small segregation coefficient, where the nonlinear instability is subcritical. The development and the suppression of instabilities are studied analytically and simulated numerically.