A precision LLRF control system for UED

An ultrafast electron diffraction (UED) facility is located at Shanghai Jiao Tong University. The layout of the UED is divided into two modules. The accelerating module has one S-band photocathode RF gun, one C-band harmonic buncher, and one C-band deflector. The power-generating module has one S-band klystron and one C-band klystron. To meet the high-precision requirements, a MicroTCA.4-based low level radio frequency (LLRF) system is used to provide a stable RF field in the cavities. In this paper, we introduce the RF distributions, LLRF system, firmware and software of the feedback controller, and field stability of the RF gun; and present an analysis of the measurement results for UED.