Double Pulse Operation of Photoinjector in Short Bunch Mode

Wai-Keung Lau^1*, An-Ping Lee¹, Chun-Yan Lin¹

¹Light Source Division, National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Wai-Keung Lau, email:wklau@nsrrc.org.tw

NSRRC photoinjector has been working regularly for testing novel accelerator and light source concepts since its first operation in 2017. It can be operated either in low-emittance mode to deliver 60 MeV electron beam of 3 -mm-mrad normalized emittance or in short bunch mode that generates 25 MeV electron bunches as short as 240 fs by means of rf bunch compression in the booster rf linac of photoinjector. The sub-picosecond beam from photoinjector in short bunch mode has been used to drive a superradiant THz free electron laser (FEL) of few tens J output radiation pulses energy. Recently, much interest is focused on structure-based and plasma-based high gradient acceleration by wake fields that are driven by intense electron beams. In this study, the possibility of generating simultaneously two neighboring electron bunches in the short bunch operation mode is being investigated. We expect the first one will have high bunch charge that can be used to drive wake field in the accelerator under test and the second bunch of lower charge to witness the field gradient of the accelerating structure. Time separation between bunches has to be adjustable by a double pulse photocathode rf gun drive laser within one rf period (i.e. 333 ps in our case). Preliminary results will be reported.

Keywords: Photoinjector, RF bunch compression, Wake field acceleration