In order to promote the studies of low emittance RF photo cathode and high gradient accelerating structures, a C-band test platform has been initialized since late 2021. In this paper, an overview of the present status and future plans of this platform is given, including a 3.6-cell C-band RF photo cathode and a C-band RF traveling-wave accelerating structure. In addition, other on-going studies on this platform, such as the test of a cryo-copper accelerating structure and the development of short pulse high gradient parallel-coupled structures, are briefly introduced.

High-brightness photoinjector has been an indispensable electron source driving X-ray free electron lasers (FEL). To improve the performance of the next-generation FEL, a high-quality electron beam with a small emittance, e.g, 0.1 micrometers for 100 pC bunch charge, will be of vital importance. A consecutive double-slit emittance meter has been proposed to measure such a small-emittance beam accurately. Analytical evaluations have been performed based upon the beam parameters of a C-band photocathode RF gun being constructed in the China Spallation Neutron Source.