The feedback control of the vertical Bridgman crystal growth process by crucible rotation: two case studies

In this work, we consider the feedback control of flows within the vertical Bridgman crystal growth process. We investigate the use of crucible rotation, via feedback control algorithms, in suppressing oscillatory flows in two prototypical vertical Bridgman crystal growth configurations-a laminar flow regime driven by a time-oscillatory furnace disturbance and a time-varying regime driven by strong buoyant forces. Proportional, proportional-integral, and input-output linearizing controllers are applied to the vertical Bridgman model to attenuate the flow oscillations. Simulation results show that for the first configuration, crucible rotation is an appropriate actuation method for feedback control. In addition, nonlinear control provides superior performance to P and PI control. For the latter case, crucible rotation is less effective, due to its exacerbating effect on the inherent time-dependent flows within this system.