EXPERIMENTAL-STUDY OF BEAM EMITTANCE AND BRIGHTNESS FROM A HIGH-POWER FIELD-EMISSION ELECTRON-GUN

A field emission electron gun using a velvet-covered cold cathode has been developed for high-power microwave generation. The emittance and brightness of electrons extracted from this gun at 10 cm behind the 36%-transparency stainless steel mesh anode have been measured by a time-integrated Cherenkov-light method. A minimum normalized emittance of 0.024π cm rad and a maximum normalized brightness of 17 kA/cm2rad2 was obtained by optimizing the diode gap distance. The normalized emittance decreases significantly as the diode average electric field increases from 600 to 650 kV/cm. The electrons in the rise-time duration were observed to have a larger brightness than that for the full pulse beam by shorting the diode voltage at the peak amplitude. The prepulse effect making beam quality worse was also studied. © 1990.