Single crystal LaB6 electron gun for variably shaped electron beam optics

Abstract

A single crystal LaB6 electron gun for variably shaped beams was developed. For the 50 A/cm2 density, 3 μm length maximum beam size, and 1 μA maximum beam current, the best electron gun characteristics were analysed. Optimum brightnesss is 2.5×105 A/cm2 sr. The product of crossover diameter and beam divergence semiangle is larger than 3.4×10−6 cm rad. Developed LaB6 guns have the following characteristics: crossover diameter is about 15 μm, beam divergence semiangle at 90% of the center intensity is larger than 3×10−3 rad and brightness varies from 7×104 to 6×105 A/cm2 sr with emission current conditions. Special features of this gun are the 480 μm tip radius and <110≳ orientation. An electron optical column for a variably shaped beam was constructed with this electron gun. Beam intensity instability for this column was smaller than ±2%/8 h without alignment or brightness servos.