  In 2008 the Cornell Electron/Positron Storage Ring (CESR) was reconfigured
from an electron/positron collider to serve as a testbed for the International
Linear Collider (ILC) damping rings. One of the primary goals of the CESR Test
Accelerator (CesrTA) project is to develop a fast low-emittance tuning method
which scales well to large rings such as the ILC damping rings, and routinely
achieves a vertical emittance of order 10 pm at 2.085 GeV. This paper discusses
the tuning methods developed at CesrTA to achieve low-emittance conditions. One
iteration of beam-based measurement and correction requires about 10 minutes. A
minimum vertical emittance of 10.3 +3.2/-3.4(sys) +/-0.2(stat) pm has been
achieved at 2.085 GeV. In various configurations and beam energies the
correction technique routinely achieves vertical emittance around 10 pm after
correction, with RMS coupling < 0.5%. The measured vertical dispersion is
dominated by beam position monitor systematics. The propagation of
uncertainties in the emittance measurement is described in detail. Simulations
modeling the effects of magnet misalignments, BPM errors, and emittance
correction algorithm suggest the residual vertical emittance measured at the
conclusion of the tuning procedure is dominated by sources other than optics
errors and misalignments.
