Low Emittance Gun Based on Field Emission

The design of an electron gun capable of producing beam emittance one order of magnitude lower than current technology would reduce considerably the cost and size of a free electron laser radiating at 0.1 nm. Field emitter arrays (FEAs) including a gate and a focusing layer are an attractive technology for such high brightness sources. Electrons are extracted from micrometric tips thanks to voltage pulses applied between the gate and the tips. The focusing layer should then reduce the initial divergence of each emitted beamlet. This FEA will be inserted in a high-gradient diode configuration couplesd with a radiofrequency (RF) structure. In the diode part the high electric field (several hundreds of MV/m) will limit the degradation of emittance due to space-charge effects. The first acceleration will be obtained with high voltage pulses (about one megavolt in a few hundreds of nanoseconds) synchronized with the low voltage pulses applied to the FEA (200-300 V in less than one nanosecond at a frequency lower than a kilohertz). This diode part will then be followed by an RF accelerating structure in order to bring the electrons to relativistic energies.