FAST METHOD FOR MEASURING POWER-DENSITY DISTRIBUTION OF NONCIRCULAR AND IRREGULAR ELECTRON-BEAMS

A fast method for measuring the power density distribution of electron beams has been developed. The method employs a refractory metal disc containing regularly spaced radial slits and a Faraday cup to measure electron beam profiles as the beam is oscillated in a circular pattern over the disc, This beam profiling method can be used for real time f ocusing along a given beam sweep orientation by monitoring one of the beam profiles. When the focus setting is satisfactory all of the beam profiles can then be stored for computed tomography (CT) reconstructio n. The CT reconstruction renders an image of the powder density distri bution and provides beam statistics as a permanent file for process co ntrol records. The process (taking similar to 1 min to perform in its entirety using a conventional PC) was used to investigate the influenc e of focus setting on the power density distribution of 5 mA electron beams operating at accelerating voltages of 80 and 140 kV. Results of these tests show the effects of beam astigmatism on the power density distribution and the optimum focus conditions for these non-circular b eams. in addition, these results show the ability of the 140 kV beam t o focus more precisely and thus produce higher power densities than th e 80 kV beam.