Angular distribution, total energy distribution, and noise measurements have been carried out on both a zirconium coated and built-up W(100) field cathode operating at high temperature (1400–1800 K). The effect of residual gas on the emission characteristics and emitter life was also measured. The results show that high brightness (∠1010 A cm−2 sr−1) operation with <10% noise levels and <1.5-eV energy spread in a 0.079-msr- beam solid angle can be achieved. Emitter longevity in excess of 1000 h in 10 nTorr (1.3 - 10−7 Pa)gas pressure has been observed.