Experiments with field-emitter arrays for free electron micro-laser applications

Propagation characteristics of beams extracted from double-gated field-emitter arrays (FEAs) were investigated. The beams were accelerated to several keV in a 15-mm long gun region and the whole beam traversed a distance of 1 m. Separate images of emitting tips were formed, when operating the focus lens of FEAs, on a fluorescent screen located at the downstream end. The images became clearer when the beam focusing was assisted by either an electrostatic or magnetic lens arranged in the transport system. A quadrupole lens was employed to determine the emittance diagram of the beam. It was verified that beamlets emitted from the tips were distributed on a straight line in the transverse trace plane. Normalized emittance of the beam thus obtained was a few times 10−7 π m rad, independently of the beam current within a measured range of 10 nA–50 μA.