Observations of electron bunching in the micro-pulse electron gun

We report on the first observations of electron bunching in the Micro-Pulse Gun (MPG). The MPG is an electron gun based on the resonant amplification of an electron current by secondary electron emission in an rf cavity. Electron emission is enhanced by a secondary emission material coated on the cavity walls and the resonant amplification creates electron bunches much shorter than the rf period. The beam is extracted through a grid and can be used as a source for rf accelerators and microwave devices. Analytic theory and Particle-in-Cell (PIC) simulation of the beam show that the natural bunching process creates one bunch for each rf period. A proof of principle experiment was designed and operated at 1.3 GHz and direct measurements of the beam confirm the existence of short bunches.