CU to dedicate facility for research and training of X-ray beam scientists

By David Brand

A remarkable facility producing some of the world's most intense X-ray beams for research, education and training will be dedicated at Cornell Tuesday, June 15. Known as G-line, it is the world's only such center operating on the central campus of a major research university.

Cornell graduate students Aaron Fleet, left, and Darren Dale have designed and built their experiments at the G3 hutch in Wilson Lab's G-line facility to study pulsed laser deposition of new materials. Robert Barker/University Photography

Built by Cornell and housing equipment purchased through National Science Foundation (NSF) grants, G-Line is dedicated to Cornell research and education in technology, biology and materials science. Ten of the university's research groups will pay annual operating expenses.

"This will generate the opportunity for learning to design new beam lines and the next generation of X-ray optics," said Joel Brock, G-Line director and professor of applied and engineering physics. "It's a thing of beauty. An amazing facility. We are so fortunate to have such a set of tools on campus."

The dedication ceremony will be at 4 p.m. June 15 at Wilson Lab, third floor terrace, followed by a tour of the G-line facility.

Four years in the building, G-line is a division of the Cornell High Energy Synchrotron Source (CHESS), a national user facility funded by the NSF. Because of its federal support, CHESS is open to all researchers on a competitive basis and currently supports roughly a thousand user visits a year. Only about a quarter to a third of the users are from Cornell. By comparison, G-line has 80 percent of its time dedicated to Cornell users, in recognition of the fact that about half the cost of the facility was borne by Cornell.

Cornell has been a leader in X-ray synchrotron radiation since the 1950s, and has greatly influenced synchrotron research. G-line presents opportunities to continue this leadership.

The X-rays are provided by the Cornell Electron Storage Ring (CESR), among the world's most powerful rings for X-ray production. The half-mile circumference ring stores counter-rotating particle beams that have been accelerated to nearly the speed of light in a synchrotron. Wilson Lab physicists study the subatomic particles created in the collisions of the beams and CHESS utilizes the X-rays produced by the beams.

The X-rays, created as a byproduct of the beams, escape through beryllium windows located at specific locations in the storage ring and are fed into experimental stations, or hutches, for use by CHESS researchers. For G-line, a new opening was cut into the ring and two X-ray beams were directed into three new hutches. The big difference between these three hutches and the nine others at CHESS is that they will be used almost entirely by graduate students for experiments that will lead to their doctorates.

The research that the high-intensity beams make possible in the three new hutches ranges from the growth of semiconductor films to measuring the time dependence of the size and shape of proteins and nucleic acids as they fold. Many of the research programs use the X-ray beams for investigating new materials, supported by the NSF-funded Cornell Center for Materials Research.

Two graduate students, Aaron Fleet and Darren Dale, have designed and built their experiments in the G3 hutch to study pulsed laser deposition (PLD). This technique uses an intense laser beam to deposit new and interesting materials, which otherwise would be difficult to grow, as thin films on surfaces such as silicon. The students' advantage over other researchers, they say, is that the equipment is permanently installed in the hutch. "Because this is the only full-time PLD installation, alignment is not a big problem. Normally it would take several days to prepare an experiment, but we are already aligned," said Fleet.

By comparison, the hutches at CHESS have a revolving number of users. "The metric of success is not the number of users, but the quality and risks and delivery of science," said Brock.

The 3,000-square-foot facility, including a 140-foot-long tunnel connecting it to CHESS, is built into the side of a hill. Cornell provided $3 million for the civil construction. The NSF awarded $2.5 million over three years for equipment, which it followed up with three other awards, the largest for $445,000. "Staying at the front of the game requires these investments," said Brock.

Much of the equipment was designed and assembled on site by CHESS staff and Cornell graduate students, including the mirror box with its rhodium-coated, silicon mirror, 1 meter in length, for focusing the X-ray beam as it comes off the storage ring. The beam is then split into two in two vacuum boxes, each containing a synthetic multilayer monochromator crystal. The beams are then focused onto the samples by separate final mirrors. Even the building's heavy concrete walls embedded with iron fragments for radiation shielding were developed at Cornell.

Said Brock, "G-line took the tricks learned everywhere else and used novel optics for novel beam lines."