New ways for influencing thermophoretic efficiency in the MCVD process

Abstract The thermophoretic efficiency in the modified chemical vapour deposition process has been experimentally studied under conditions of changing temperature and velocity field in the silica deposition tube. The cooling of the tube by a stream of air, deposition under the reverse torch traverse and induction of a circular flow in the tube have been studied. Results of the experiments were explained on the basis of the Walker thermophoretic model and under the assumption that the amount of the deposited glass is determined by chemical equilibrium. Considerable increase of the overall thermophoretic efficiency was observed when cooling by the air stream was used. The derived theoretical model can account for these results.