Beam Dynamics Study of a Photo-Injector at Wuhan Light Source

A photo-injector is under development at Wuhan Light Source (WHLS) to provide beams for the 1.5 GeV storage ring proposed as a fourth-generation synchrotron radiation light source and a future free electron laser (FEL) facility. The photo-injector and the following LINAC will be able to produce electron beams with low emittance (2 mm·mrad), high bunch charge (~1 nC), small energy spread (0.5%) , and short bunch length, which meet the requirements of the ring injection and the FEL operation simultaneously. The injector boosts the bunch energy to 100 MeV, which is mainly composed of a photocathode RF gun working at 2998 MHz, two solenoid coils for emittance compensation, and two 3-meter-long 2998 MHz traveling-wave (TW) accelerator units. Beam dynamics optimization of the photo-injector is presented in detail, which has been performed with multi-objective genetic algorithm (MOGA) combining theoretical analysis and ASTRA code. After optimization, the 95% projected transverse emittance has reached as low as 0.45 mm·mrad with an RMS bunch length of about 1.0 mm at a bunch charge of 1 nC.