Power Density of Optimally Focused Space-Charge-Limited Electron Beams

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Abstract
Factors affecting the power density of optimally bundled electron beams used for the welding, cutting, and machining of solid material are described. The power density and spot size of these beams are expressed as a function of acceleration voltage, beam current, and electron optical characteristics of the system. Assuming that the spherical aberration of the beam-focusing lens system limits the spot size of the space-charge-limited beam, the power density under optimum conditions increases approximately with the fifth power of the acceleration voltage, and decreases with the 7/4 power of the beam current. A criterion is also given which enables one to determine whether the electron beam at its impact on the workpiece is space-charge-limited or not. Some considerations are given to the neutralization of the electron space charge by ions originating from the background pressure of the vacuum system.

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