Nanoseconds field emitted current pulses from ZrC needles and field   emitter arrays
  The properties of the electron source define the ultimate limit of the beam quality in linear accelerators like Free Electron Lasers (FEL). The goal is to develop an electron gun delivering beam emittance lower than current state of the art. Such a gun should reduce the cost and size of an X-ray Free Electron Laser (XFEL). In this paper we present two concepts of field emitter cathodes which could potentially produce low emittance beam. The first challenging parameter for such cathode is to emit peak current as high as 5 A. This is the minimum current requirement for the XFEL concept from Paul Scherrer Institut.1 Maximum current of 0.12 A and 0.58 A have been reached respectively with field emitter arrays (FEA) and single needle cathodes. Laser assisted field emission gave encouraging results to reach even higher peak current and to pre-bunch the beam. 
R. Ganter, R.J. Bakker, R. Betemps, M. Dehler, T. Gerber, J. Gobrecht,   C. Gough, M. Johnson, E. Kirk, G. Knopp, F. Le Pimp...