Sugawara emphasizes that cost is the primary motivating factor for building a photon-photon collider first. The ILC can’t materialize unless organizers can get governments and funding agencies to support it. With high-energy physics suffering budget cuts world wide, and the LHC still trying to get on its feet, it’s a tough time to pitch such an idea. Sugawara predicts that the cost of a photon-photon collider would be well under half that of the ILC, making it more appealing to potential funders.
“If there is a financial threshold over which a government will not fund the ILC, and if that threshold is half the cost, then a photon-photon collider might make sense,” says Tor Raubenheimer, head of the Accelerator Physics Group at SLAC. But if governments are willing to fully fund the ILC, Raubenheimer says it is unlikely that the community will hold back from building it. Sugawara supports building one either way.
Then again, Sugawara argues that a photon-photon collider could also advance accelerator technology before the ILC is built. “From the time that it is decided to build a particle accelerator to the time the physics actually starts can easily be a decade,” Raubenheimer says. Right now the ILC would operate at 500 GeV, but by the time it is fully constructed scientists may well want it to operate at 1 or 2 TeV. Such an upgrade might not be fiscally or technologically possible on a fully constructed machine. As Sugawara puts it, “We would build the machine to study the machine.” In other words he believes the potential collider would advance accelerator technology and understanding before a major investment is made in the ILC.
I'm not sure if any of these can be answered yet. It still depends very much on what the LHC will produce, so at some level, the future of what the next major project for the HEP community depends very much on the results coming out of the LHC, be it positive or negative. Till then, I don't see any impetus from any funding agency (certainly not here in the US) to make a decision to build anything. But then again, countries like Japan and China can make their own unilateral decision and run away with it, leaving Europe, and especially the US, holding an empty bag.