Shifting gears for timing at SNS?

As members of the team for timing systems at the Spallation Neutron Source (SNS) and the team for operating choppers at LANSCE, we were surprised by the results of timing system simulations that overturned some of our preconceived notions regarding choppers and accelerators. We feel these concepts may well benefit from the review of peers interested in such timing issues. We will discuss three propositions: Timing for pulsed sources should be planned backwards starting with extraction at a fixed phase and working toward the leading edge of the beam pulse. Accelerator triggers and storage ring extraction offer only marginal benefits to accelerator-based spallation sources. The storage ring RF should be phase shifted to provide extraction without the one orbit timing uncertainty. The rational for each of these propositions is presented. (author)