Research opportunities at the upgraded HIS facility

The High Intensity γ -ray Source (HI γ S) is a joint project between the Triangle Universities Nuclear Laboratory (TUNL) and the Duke Free Electron Laser Laboratory (DFELL). This facility utilizes intra-cavity back-scattering of the FEL light in order to produce intense γ -ray beams. An upgrade which allows for the production of γ -rays up to energies of about 100 MeV having total intensities in excess of 108/s is essentially complete. The primary component of the upgrade is a 1.2 GeV booster-injector which makes it possible to replace lost electrons at full energy. In addition, an upgrade of the present linear undulator to a helical system has made it possible to produce nearly 100% linear and circularly polarized beams. The full system was commissioned in the early part of 2007. A nuclear physics research program using beams at energies below 50 MeV commenced in the fall of 2007. The proposed experimental program includes low-energy studies of nuclear reactions of importance in nuclear astrophysics as well as studies of nuclear structure using the technique of nuclear resonance fluorescence (NRF). Few-body nuclear physics problems will also be addressed by studying photodisintegration of d, 3He and 4He. Future double-polarization experiments include a study of the Gerasimov–Drell–Hearn Sum Rule for the deuteron and 3He, and an extensive Compton scattering program designed to probe the internal structure of the nucleon. A major focus of these studies will be the measurement of the electric and magnetic polarizabilities as well as the spin-polarizabilities of the proton and the neutron. This review will describe the principles of operation of the upgraded facility, followed by a description of the performance which has been achieved to date, and a projection of the performance anticipated in the near future. Following this, we will review several of the research areas of nuclear physics which are accessible using this facility, and describe both the results to date and proposed experiments being developed for the future.