(Knoxville News-Sentinel (TN) Via Acquire Media NewsEdge) July 14--OAK RIDGE -- The Spallation Neutron Source is operating like it should, and that's not as simple as it sounds.
Last month -- eight years after construction was completed and seven years after operations began -- the SNS finally achieved the beam power for which it was designed: 1.4 megawatts. Even at lower power levels, the accelerator-based center for materials research set all sorts of records, and scientists from around the globe flocked to Oak Ridge to do experiments with the richest source of neutrons available. It's been a productive journey, but even more is expected with the higher beam power.
Kevin Jones, who heads the Research Accelerators Division at Oak Ridge National Laboratory, noted that the SNS actually reached 1.4 megawatts last September -- for about 30 minutes -- but the system was too unstable to continue.
On June 26, following months of gradual power increases, the SNS operated at 1.4 megawatts for about 24 hours while users conducted their experiments. That was a big milestone to achieve a few days before the systems were shut down for the summer maintenance period.
When the SNS restarts in mid-August, it's anticipated that the power of the proton beam will be sustained at 1.4 megawatts. That will translate into more neutrons for the scientific users, which of course is the whole point. With the higher neutron flux, researchers are able to do more experiments and, in some cases, use smaller samples or tackle challenging studies that wouldn't otherwise be possible.
The Spallation Neutron Source, which occupies about 80 acres atop Chestnut Ridge, has elaborate processes in which particles are accelerated, stripped of their electrons and jammed into a storage ring. The resulting energy is unleashed as powerful pulses of protons on a liquid mercury target. This happens 60 times a second, and each strike on the target releases trillions of neutrons, which are then herded into research stations. Super-sophisticated instruments are able to analyze the neutron movements as they pass through the material samples.
Scientists use these neutron-scattering techniques to explore the essence of materials -- their structure, their properties, their atomic behavior -- and this information can then be used to make better materials or make better use of existing ones.
Thomas Proffen, director of neutron data analysis and visualization, cited a recent experiment at SNS that identified a link between magnetism and superconductivity that is helping scientists better understand how superconductors work. Running at higher power will accelerate the project by studying more samples and enabling systematic studies of a sample under varying conditions, such as different operating temperatures, he said.
The use of smaller samples may also help with studies of the atomic structure of proteins, Proffen said.
"Understanding the structure of binding sites in a protein is the key to rational drug design -- in other words making more effective drugs," he said. "Recent work includes structural studies to create better drugs fighting AIDS and bacterial infections."
ORNL Director Thom Mason, who once served as director of the SNS, said he believes the $1.4 billion research facility is "really hitting its stride" and serving an increasingly broad community of scientific users. New analytical instruments are coming online at the SNS, adding to the research capabilities and expanding the opportunity for new users, he said.
Each time a new research instrument had been made available for experiments, the demand from the scientific community has immediately outstripped the time available, Mason said.
A second target station that would double the SNS capacity and add to the capabilities is in the planning stages, and a Department of Energy review approved the "mission need" for such an expansion. Mason acknowledged the biggest hurdle will be finding the funding for the billion-dollar project in the current budget climate. In the meantime, some of the technical issues are being studied -- in concert with the researchers -- so that the lab is ready to proceed when the time comes.
In addition to upping the beam power to 1.4 megawatts, the SNS team is looking at ways to extend the life of the stainless-steel vessel that holds and circulates the liquid mercury target.
A couple of years ago, the target vessels were failing at a disturbing rate, which forced the lab to lower the beam power for a while to help preserve the vessels while additional backups were manufactured. A welding issue was identified as the problem for the premature failures, but the lab would still like to get longer-lasting vessels because each one costs more than $1 million.
A new target vessel with a different internal design was installed recently and will be tested when the SNS restarts next month, Jones said.
"We'd rather use one a year rather than two a year," he said.
The new design is supposed to allow the mercury to flow more efficiently inside the target vessel and reduce the rate of internal damage from "cavitation" -- bubbles in the mercury collapsing and sending energy against the walls.
Until the new design has been proved, however, ORNL will continue to have new vessels of the old design manufactured as backups, Jones said.
"I'm confident that we have ourselves covered," he said.
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