Design of a high-current 2.856-GHz RF photocathode gun for wake-field acceleration

A design study of a 2.856-GHz, 1.5-cell RF photocathode gun is described in this paper. The study was motivated to produce short electron bunches with very high beam current, low transverse beam emittance, low energy spread, and short longitudinal bunch length. With the choice of a 10-nC bunch charge and 45 degrees injection phase, a peak electric field of 125 MV/m is produced on the symmetry axis. In order to overcome the emittance growth due to space-charge effect, focusing solenoids are employed in various places, resulting in a normalized rms transverse emittance of 10.19 cm-mrad and an rms bunch length of 0.70 mm at a distance of 90 cm from the photocathode.