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Abstract

In an electron beam evaporation system utilizing a grid to control electron flow, non-uniformities in vapor density caused by periodic trapping of electrons near the filament due to the magnetic field produced by alternating heater current are substantially reduced either (1) by out-of-phase grid modulation which increases electron flow from the filament at times when the alternating magnetic field operates to trap electrons, (2) by using a high frequency a.c. source for heating the filament thereby to smooth out the effects of the a.c.-produced magnetic field, or (3) by using an auxiliary cathode heated by the bombardment of electrons from a filament spaced from the cathode by a distance which removes the cathode from the magnetic field produced by the a.c. heating of the filament. In one emobodiment, demodulation of vapor density is employed in laser isotope separation to provide a temporally uniform atomic uranium vapor.

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First Claim