Study on Clarification of Large-Area EB Irradiation Phenomenon by Electron Track Analysis

In large-area electron beam (EB) irradiation method, uniformly high energy density can be obtained without focusing the beam. Large-area EB can be used for melting and evaporating metal surface instantly. It was clarified that high efficient surface finishing of metal mold steels, ceramics and cemented carbides was possible by the large-area EB irradiation. Furthermore, the tip of convex shape was often rounded after large-area EB irradiation with remarkable material removal at the tip. This phenomenon is probably caused due to the heat accumulation and electrons concentration at the tip. However, electrons behavior near the workpiece surface during large-area EB irradiation has not yet been clarified. In this study, electron track analysis was conducted in order to clarify electrons behavior during large-area EB irradiation. At first, analytical model of the large-area EB irradiation apparatus was built. Then, the EB diameter on the workpiece surface was experimentally measured with different energy density in order to evaluate the accuracy of our analytical model. The calculated results of EB diameter were in good agreement with the experimental ones. In addition, the electrons concentration phenomenon at the tip of convex shape was clarified by calculating energy density distribution on the surface obtained with electron track analysis. The analytical results indicated that the energy density increased from edge to tip of convex shape, while the energy density was constant in the case of planar shape. Experimented results also showed that removal thickness increases with high relative permeability. These results were similar tendency to the energy density distribution. Therefore, electrons concentration on the tip could be simulated by the electron track analysis.