One possible location for placing a linac inside the Tevatron ring as a test facility for the ILC.

Before the International Linear Collider can be built, physicists and engineers must prove that the proposed baseline design will achieve the desired physics, requiring testing and R&D at laboratories and institutions around the world. As part of this process, Fermilab's Mike Church recently shared with attendees, at a weekly ILC R&D meeting, one possible proposal for ILC Test Beam Facilities that would utilize the lab's already existing infrastructure.

In an early stage of development and not yet endorsed by Fermilab management, the proposal will continue to be evaluated and reviewed not only by the lab but also by the Global Design Effort and the Department of Energy. "This is a work in progress," Church said. "We haven't thought too seriously about cost, location or a timeline yet. The tiered proposal allows you to make more rational decisions about what you're getting."

Put together by a team of scientists in March 2006, Church outlined a five-tiered plan in which each facility requires the previous one to be developed. With parts of the proposal already in action at Fermilab, the 5-tiered proposal is as follows:

1. e- source: Continue the ongoing R&D at the AZero photoinjector to study emittance preservation in a superconducting linac.
2. e- source + 3 cryomodule superconducting linac: The basis for a system test of a single RF unit, consisting of a modulator, transformer, klystron, RF distribution, 3 cryomodules and feedback. As the current plan for the Fermilab ILC Test Area at the New Muon Lab (ILCTA – New Muon), this facility can be used to test cryomodules with full beam intensity up to approximately 750 MeV.
3. e- source + 20 cryomodule superconducting linac: This 5 GeV linac, consisting of approximately 20 cryomodules and requiring about 220 metres in length, would be adequate to test emittance preservation techniques and alignment tolerances for the ILC – a primary beam physics concern for the machine.
4. e- source + 20 cryomodule superconducting linac + 5 GeV e- damping ring in the Tevatron tunnel: After 2009, the majority of the Tevatron tunnel will be unused. The 5 GeV linac can be built inside the Tevatron ring, serving as an injector to a 5 GeV damping ring inside the 6 km Tevatron tunnel – something that will never have been done before with these specific conditions.
5. e- source + 20 cryomodule superconducting linac + 5 GeV e- damping ring + positron source and associated beamlines: Using the positron source to produce the opposite of electrons, the linac can then accelerate them to 5 GeV. From there, the positrons can be injected into the e- damping ring to study electron cloud effects – a very uncertain issue.

Emphasizing that this proposal is not final, Church discussed the number of questions that surround building test facilities at Fermilab. Whether the test facility should be located underground, for example, to study such issues as ground motion, temperature and humidity control is one of the questions that scientists will continue to assess.

-- Elizabeth Clements