Optimized design of an consecutive double-slit emittancemeter for the c-band photocathode rf gun

To enhance the performance of the next generation of X-ray free electron lasers (XFEL), it is essential to produce a high quality electron beam with a low emittance, for instance, below 0.2 mm-mrad for a 100 pC bunch charge. In order to demonstrate the fundamental techniques required for future FEL facilities, a C-band photoinjector test facility has been constructed aligning with the Southern Advanced Photon Source (SAPS) pre-research project. An emittancemeter based on the consecutive double-slit-scan concept has been proposed and designed for determining such small emittance. This paper presents the further optimization of the primary parameters of this emittancemeter employing numerical simulations in the presence of the measured motion accuracy and the expected observation resolution.