Magnetic damping of melt motions during Bridgman crystal growth in microgravity

For a typical Bridgman semiconductor crystal-growth process in space with a 0.2 Tesla axial magnetic field, the velocity in the melt motion driven by the residual accelerations is so small that nonlinear inertial effects and convective heat transfer are negligible, and the governing equations are linear. Therefore the melt motions driven by (1) the time- averaged or steady residual acceleration, (2) the continuous, random fluctuations of acceleration or g-jitters, and (3) the isolated spikes of much larger acceleration due to thruster firings, etc., are decoupled and can be treated independently. In addition, the solution for any instantaneous orientation of the acceleration vector is given by a time-dependent superposition of two solutions for an axial acceleration and a transverse acceleration. Solutions are presented for the magnetically damped buoyant convections driven by the axial and transverse components of the steady acceleration, the g- jitters and the spikes of larger acceleration. The axial magnetic field provides much stronger damping of the transverse vorticity than of the axial vorticity, so that the melt motion may be quite different from that without magnetic damping.