Superconducting RF Gun cavities for large bunch charges

The first electron beam of an RF gun with a 3.5 cell superconducting cavity is expected in July 2007 in FZD. This cavity has been designed for small bunch charges. In this paper we present the design of a similar cavity and of 1.5 cell gun cavities for large bunch charges. For a charge of 2.5 nC, which is the design value of the BESSY-FEL, and a bunch length of 21 ps a projected transverse emittance less then 1 πμ has been obtained (without thermal emittance).