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The European Spallation Source Only two years have passed since ORNL's Spallation Neutron Source began to generate the most intense pulsed neutron beams in the world, but the race to build a successor to the SNS—or at least a worthy competitor—has already begun. In Europe, interest is growing in building a "next-generation" spallation source. Recently, delegations from all three of the groups competing for the privilege of hosting the ESS—Bilbao, Hungary and Scandanavia—have visited the ORNL on fact-finding missions. The visitors are not only interested in the scientific programs at the SNS, but also in the impact the multibillion dollar facility has had on the region, including the local economy and schools. ORNL Director, Thom Mason, who headed up the SNS project during most of its planning and construction, recalls that "When we were building SNS, we benefitted a lot from the interactions we had with other operating facilities around the world—in Europe primarily, and in Japan. So now that the Europeans are contemplating building a source, they're trying to draw on our experience in the same way we drew on theirs." Mason stresses that there's more involved in decisions about whether or where to build a facility than purely scientific considerations. "There's an element that's related to scientific collaboration and solving technical problems," says Mason, "but building a facility of that scale is also a big deal for the region economically, so the visits to some extent have been oriented more around the economic development impact of a major R&D facility." The ESS website suggests that, because any European spallation source is not likely to come online before 2017, the European scientific community should plan on building a facility that's five times as capable as the SNS in many areas. So, will that sort of capability make the SNS obsolete in less than ten years? Not likely, according to Mason: "The European design goal is a five megawatt facility. SNS is currently 1.4 megawatts, but we're working on a power upgrade to increase that. So we're a bit of a moving target. The European spallation source certainly won't be five times as powerful as the SNS by the time it's finished." Mason also explained that the proposed European spallation source is a different type of neutron source than the SNS. "The proposed European machine is a long-pulse source and the SNS is short-pulse," Mason said, "so it has different characteristics. Getting to five megawatts, for example, is easier with a long-pulse source. The second target station planned for the SNS would be a long-pulse target. I'm confident that by the time the ESS is built the SNS will have moved ahead, so we're going to stay competitive under any scenario." Because the construction of a worldclass neutron source is such a massive undertaking, both the European spallation source and the SNS are designed to be upgraded as technology improves. "Eventually we will hit some sort of limit," says Mason, "but accelerators tend to have capabilities that go beyond what was originally thought possible—just because the technology improves." The SNS has a 20-year plan for upgrades that includes doubling the beam power, doubling the number of instruments with a second target station, and developing a long-pulse source. "That doesn't mean we won't be able to upgrade it after that," says Mason, "it's just that, at that point in time, the technology is sufficiently far out that it's hard to know what the path will be. That'll keep us busy for 10-20 years. After that it will depend on how the technology evolves."
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