Generation of Picosecond Pulse Electron Beams

Picosecond pulse electron beams were generated by means of a transverse-type gate and a buncher. The 20 keV beam was deflected by a 1 GHz symmetrical reentrant cavity and chopped by a slit into several tens picosecond pulses. These pulses were bunched by a 4 GHz reentrant cavity. The pulsed beam was then deflected by the other 1 GHz x–y deflectors and finally reached the screen, where the pulse width was measured by comparing the lengths of two chopped arcs with that of the unchopped full circle. A minimum pulse width of 6 psec was recorded. It was observed that as the deflecting voltage of the transverse gate increases, the pulse width decreases at first, reaches a minimum, and then increases. This can be explained by the longitudinal velocity modulation due to the fringing field of the deflector. When the beam chopped by the transverse gate was injected to the longitudinal gate, the maximum phase compression ratio was less than 5; this is also explained by the above-mentioned effect.