Realization of limited-area cathodes and their performance in an electron optical column

Limited-area cathodes based upon impregnated dispenser cathod material have been investigated in an electron optical column at accelerating voltages of up to 30 kV. A peak axial brightness of about 6 X 105 A/cm2 sr was obtained at this voltage using a flat cathode. Brightness values greater by a factor of 10 were measured using a conical limited-area cathode with a tip radius of curvature of 0.075 mm. The latter measurements were affected by space-charge spreading in the beam. 7 refs., 6 figs., 1 tab