Current operations at Fermilab use six rings: Booster, Accumulator, Debuncher, Recycler, Main Injector and Tevatron. The descriptions of Project X and SNuMI explain how the Main Injector would be used to produce an intense source of neutrinos, with nearly 10 times the intensity of the current source. Besides the Main Injector, the following examples show how an expanded program could use additional existing rings at Fermilab.
Debuncher slow extraction
The Antiproton Debuncher ring could provide an 8 GeV slow-extraction facility with parameters appropriate for a muon-to-electron conversion experiment. Protons could be provided either from the Accumulator (SNuMI) or from the Recycler (Project X). An RF system within the Debuncher would confine the protons to a single bunch, and a slow extraction system would spill the beam over the 1.33-1.4 second cycle time. Operating with a single bunch, the circumference of the Debuncher creates a spill structure containing a ~100 ns pulse every 1.6 μs. With the SNuMI configuration, total delivered beam would be 1.35×1013 every 1.33 seconds, with a corresponding 16 percent reduction in available protons at 120 GeV. If Project X were used to deliver protons, any number up to the full complement of 2.2×1014 every 1.4 seconds could be made available with no impact on the 120 GeV program.
Taking protons at 120 GeV directly from the Main Injector, the Tevatron could be converted to a 120 GeV "stretcher" ring to provide very high (>90 percent) duty factor beams for a variety of precision frontier experiments. The Tevatron Stretcher provides an independent program that could be used with or without the SNuMI or Project X intensity upgrades. However, the program would result in a tax on the Main Injector-based neutrino program.
A possible scenario would use two Main Injector cycles, at 3.75×1013 protons per pulse, providing 7.5×1013 protons in the Tevatron at 120 GeV. This beam is not accelerated, but rather is slow extracted over roughly 60 seconds. The duty factor would approach 95 percent. This scenario would deliver a total of about 3×1019 protons in a year, representing approximately a five percent diversion of protons from the SNuMI or Project X neutrino program. Because the delivered intensity would be about a factor of 2.5 beyond the highest intensity ever stored in the Tevatron, the laboratory would need to address a number of intensity-related issues. In addition, this scheme would require the design and implementation of a 120 GeV resonant extraction system.
The Tevatron Stretcher and associated extracted beam lines would require a one-to-two year construction period at an appropriate time following completion of Tevatron collider operations.
Tevatron high-energy neutrino facility
The Tevatron could operate at high intensity and high energy in fixed-target mode. The science program described in Chapter 4 would require a minimum beam energy of roughly 800 GeV, with a delivered intensity of at least 4×1019 protons per year. The minimum cycle time of the Tevatron in fixed-target mode is about 40 seconds, establishing the basic per-pulse intensity requirement.
A possible scenario would resemble the Stretcher scheme described above. Two Main Injector cycles, at 3.75×1013 protons per pulse, are transferred to the Tevatron at 120 GeV. This beam is accelerated and delivered to a neutrino target via a fast-spill mechanism. Based on a minimum Tevatron cycle time of 40 seconds, the scheme would deliver a total of about 4×1019 protons per year, approximately a five percent diversion of protons from the SNuMI or Project X neutrino program. The same intensity issues associated with the Tevatron Stretcher would apply. Several other technical issues would also require resolution, including development of the fast-extraction scheme, mechanisms for loss control and collimation, recommissioning of the CZero high-intensity abort, and a reliability analysis.
Tevatron fixed-target operations would require one to two years to implement at an appropriate time following completion of Tevatron collider operations.