Spatial distribution of copper vapour flux during strip electron beam evaporation

The experimental measurements of spatial distribution of copper vapour flux from a two-dimensional source ( D = 10.4 mm; L = 97 mm) was carried out by impinging electron beam from 130 mm strip electron gun. The copper vapour was generated in the transition flow regime of rarefied gas dynamics and experimental measurements were carried out by using deposition technique, at locations ( r ), where free jet expansion is expected to show three-dimensional behaviour ( D << L ~ r ). Reported analytical expressions based on Knudsen's cosine law for two-dimensional sources with uniform temperature were reviewed and used for the interpretation of experimental data. The inadequacy of these expressions is pointed out by noting the systematic deviation of the calculated values from the observed ones with receding position of the vapour collector from normal line of the source. Attempts are made to interpret experimental data by dividing source area into small elemental areas and integrating contribution from each such area on to the collectors. The experimental data could be best fitted within ±5% with cos n ψ distribution with n = 1.77 and uniform source temperature of 1694 K or with n = 1.75 with temperature distribution along and across the focal strip with an average temperature of 1687 K as compared to the measured value of 1685 K.