Temporal evolution of beam emittance from a field-emission electron gun

The temporal evolution of the beam emittance and beam brightness from a field-emission electron gun (1.3 MV, 0.5 kA, 30 ns) has been measured with nanosecond time resolution by using a novel Čerenkov-electro-optic diagnostic. Observations show that guns provided with velvet-backed cathodes behave differently than, and are superior to, the more conventional graphite cathodes.