How to Reach a Thousand-Second in-Plane Polarization Lifetime with<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>0.97</mml:mn><mml:mtext>−</mml:mtext><mml:mi>GeV</mml:mi><mml:mo>/</mml:mo><mml:mi>c</mml:mi></mml:mrow></mml:math>Deuterons in a Storage Ring

We observe a deuteron beam polarization lifetime near 1000 s in the horizontal plane of a magnetic storage ring (COSY). This long spin coherence time is maintained through a combination of beam bunching, electron cooling, sextupole field corrections, and the suppression of collective effects through beam current limits. This record lifetime is required for a storage ring search for an intrinsic electric dipole moment on the deuteron at a statistical sensitivity level approaching 10^{-29} e cm.