  The High Intensity Gamma-ray Source (HIGS) at Duke University is an
accelerator-driven Compton gamma-ray source, providing high flux gamma-ray beam
from 1 MeV to 100 MeV for photo-nuclear physics research. The HIGS facility
operates three accelerators, a linac pre-injector (0.16 GeV), a booster
injector (0.16-1.2 GeV), and an electron storage ring (0.24-1.2 GeV). Because
of proximity of the booster injector to the storage ring, the magnetic field of
the booster dipoles close to the ring can significantly alter the closed orbit
in the storage ring being operated in the low energy region. This type of orbit
distortion can be a problem for certain precision experiments which demand a
high degree of the energy consistency of the gamma-ray beam. This energy
consistency can be achieved by maintaining consistent aiming of the gamma-ray
beam, therefore, a steady electron beam orbit and angle at the Compton
collision point. To overcome the booster leakage field problem, we have
developed an orbit compensation scheme. This scheme is developed using two fast
orbit correctors and implemented as a feedforward which is operated
transparently together with the slow orbit feedback system. In this paper, we
will describe the development of this leakage field compensation scheme, and
report the measurement results which have demonstrated the effectiveness of the
scheme.
