Beam dynamics in RF-gun cavity with a modified first cell

The result of beam dynamics simulation with bunch charges up to a few tens pC in superconducting linaer accelerator for ELBE project [1] is presented. The accelerator consists of 3+1/2 TESLA cells RF-Gun and two 9-cell TESLA cavities. It is shown, that the change of a flat back wall of the half cell with cathode in its center by a conical back wall results in reduction of transversal bunch sizes and also in reduction of emittance at the accelerator exit by a factor of 20.