UPGRADE OF THE RF PHOTO-INJECTOR FOR THE DUKE STORAGE RING

The Duke FEL and HIγS (High Intensity Gamma-ray Source) facility consists of a linac preinjector, a booster injector, and a main storage ring. The booster injector and storage ring are operated with a wide range of beam energies (240 MeV - 1.2 GeV). The electron beam source located at the beginning of the linac is a 2.856 GHz microwave photo-injector with a LaB6 cathode which produces 1 ns long pulses with a typically 0.1 nC of charge per pulse. The operation of a photo-cathode gun is important for minimizing the radiation background and reducing the amount of radiation shielding necessary for the full-energy, top-off booster injector. A reliable, effective and clean injection of the booster injector has been realized since 2006. Recently, substantial improvements have been made to the photo-cathode and linac, including the improvement of the nitrogen drive laser, development of a driver laser optical transport and beam monitoring system, and optimization of the cathode heater setting to minimize the thermionic emission. A beam charge measurement system based upon Faraday cup detectors and sample-and-hold electronics has also been developed. In this paper, we present the impact of these upgrades on everyday operation and discuss possible further modifications of the Duke linac preinjector.