Design of the initial emittance measurement system for Multi-Alkali photo cathode

We develop the electron gun which is put a photo cathode and superconducting RF cavity to develop the high repetition X-rays free-electron laser (XFEL). It is desirable that the photo cathode in superconducting RF cavity is operated under low temperature like case of the cavity. Operating under low temperature makes decrease a thermal emittance of photo cathode. We pay our attention to this point and manufacture the Multi-Alkali photo cathode and the initial emittance measurement system of DC electric field mode. In this paper, we report about the characteristic of the film formation device of the Multi-Alkali photo cathode, the result of film formation examination and the conception of the initial emittance measurement system. (author)