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We report on the design of the CIBER-X source' which is a new laser driven table-top ultrashort electron and x-ray source. X-ray pulses are produced by a three-step process which consists of the electron pulse production from a thin metallic photocathode illuminated by picosecond 213 nm laser pulses with 16 ps duration. The electrons are accelerated in the diode by a cw electric field of 11 MV/rn, and the photoinjector produces a single 70-100 keV electron pulse of O,5nC and 2O A peak current at a repetition rate of 10 Hz. The gun is a standard Pierce diode electrode type, the electrons leaving the diode through a hole made in the anode. The electrons are then transported along a path 2O cm long, and are focused by two magnetic fields produced by electromagnetic coils. Finally, the x-rays are produced by the impact of electrons on a massive target of Tm. Simulations of geometrical and energetic characteristics of the complete source were done previously with assistance ofthe code PIXEL1. Finally, experimental performances ofelectron and x-ray bursts are discussed.

The space-charge phenomenon in the diode of a photoinjector induces simultaneously temporal and spatial dispersions of the electrons burst in pulsed regime. They are higher when the initial pulse duration is shortened. Here, we present the results of temporal dispersion obtained by computer simulation and we give a simple scaling law accounting for it. This law can be used to compare durations of electron pulses at the cathode and anode in any well-defined operation set, in space-charge regime.

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