High-power inverse Compton γ-ray source at the Duke storage ring

A 1.1 GeV electron storage ring dedicated for UV-VUV FEL operation was commissioned last year at the Duke University Free Electron Laser Laboratory (DFELL). The UV-VUV OK-4 FEL project, based on the collaboration of the Duke FEL Laboratory and Budker Institute for Nuclear Physics (BINP, Novosibirsk, Russia) is under way. The OK-4 FEL has arrived at the Duke FEL Laboratory from Novosibirsk and is in the process of installation. High average intracavity power and natural synchronization of electron and optical pulses in the OK-4 FEL allow the production of intense inverse Compton (gamma) -rays (5-150 MeV) on the return pass of the optical pulse. The projected intensity of this (gamma) -ray source allows high energy resolution with simple geometric collimation of the (gamma) -rays. The wide tunability of the OK-4 FEL also allows us to control the (gamma) -ray energy. In this paper we discuss the processes involved in (gamma) -ray production, the influence of beam parameters and geometry on (gamma) -ray energy spread, and present projected performance of the Duke/OK-4 inverse Compton (gamma) -ray source for two simple cases. The studies reported in this paper were performed in 1993. Results were presented at the 1994 Free Electron Laser Conference (22-26 August 1994, Stanford, CA) but were published only as internal DFELL reports. A group of scientists from the Triangle University Nuclear Laboratory (TUNL) also ran independent simulations in 1994 which confirm our predictions. A workshop on the DFELL-TUNL (gamma) -ray facility was held in Durham from December 16-17, 1994 to discuss unique features of this facility and its utilization for nuclear physics and pion spectroscopy.