SNuMI uses antiproton facilities freed up at completion of the Tevatron collider program to develop a more intense proton source for NuMI. The Antiproton Accumulator would "momentum-stack" protons delivered from the Booster. The momentum-stacking process is inherently more efficient in its use of longitudinal phase space than the "slip-stacking" process that will be used during the NOνA era. This increased efficiency supports the higher proton throughput of SNuMI.
The SNuMI scheme momentum-stacks three Booster batches in the Accumulator and then transfers them to the Recycler. This process repeats six times via "boxcar" stacking in the Recycler. The accumulated 18 batches are transferred from the Recycler to the Main Injector in a single shot. Because the Booster cycles at 15 Hz, the Recycler accumulation process takes 1.33 seconds. The accumulation process takes place while the Main Injector is accelerating, fast-extracting beam to the neutrino target and ramping down for a new load. A 1.33 second cycle time leads to a beam power of 1.2 MW. Since this scheme uses all available Booster cycles, no additional protons are available for an 8 GeV program without diversion from the Main Injector. However, SNuMI is compatible with reconfigurations of the Debuncher ring and/or the Tevatron to support slow-spill programs at 8 or 120 GeV respectively, and with the Tevatron high-energy neutrino facility.
SNuMI could probably be constructed over a two-to-three-year period following completion of Tevatron collider operations. While it would support some of the neutrino- science and precision-physics goals, the SNuMI plan would require continued use of the existing 8 GeV Booster and 400 MeV Linac accelerators, which date from the 1972 start of beam operations at Fermilab. These accelerators' aging components have led to reliability issues over recent years. Thus, SNuMI entails some risk of operational down time or failures and does not invest in a longer-term program of experiments.