  In this paper, we demonstrate the connection between a magnetic storage ring
with additional sextupole fields set so that the x and y chromaticities vanish
and the maximizing of the lifetime of in-plane polarization (IPP) for a
0.97-GeV/c deuteron beam. The IPP magnitude was measured by continuously
monitoring the down-up scattering asymmetry (sensitive to sideways
polarization) in an in-beam, carbon-target polarimeter and unfolding the
precession of the IPP due to the magnetic anomaly of the deuteron. The optimum
operating conditions for a long IPP lifetime were made by scanning the field of
the storage ring sextupole magnet families while observing the rate of IPP loss
during storage of the beam. The beam was bunched and electron cooled. The IPP
losses appear to arise from the change of the orbit circumference, and
consequently the particle speed and spin tune, due to the transverse betatron
oscillations of individual particles in the beam. The effects of these changes
are canceled by an appropriate sextupole field setting.
