The Department of Energy's Jefferson Lab, located in Newport News, Va., is putting the finishing touches on a 10-kilowatt upgrade that will make its Free-Electron Laser 250 times more powerful, in terms of average power, than any other existing FEL. Experiments in photochemistry and atomic physics that thus far haven't been possible will become so, as should a series of advanced industrial applications. The military is also keenly interested in potential defense applications: the Navy contributed more than $18 million over the last three years and the Air Force roughly $5 million to the improvements. Additional monies have been provided by the state of Virginia and NASA.
"Calling it an upgrade is a bit of a misnomer," says FEL program manager Fred Dylla. "We've changed 90 percent of the hardware in the machine. We've gone beyond just tweaking. This is a significantly new machine."
A new cryomodule was added to the linear accelerator, or linac, portion of the laser, and a new electron-gun injector has been installed and commissioned. Early in May, the first electron beam was attained. Since then, beam has been transported through the linac and optimized. First lasing was achieved on June 17, followed by a week of initial laser-light "characterization," or analysis. Early in July the last of the electron-beam recirculation system was installed, and fine-tuning is now underway. The goal is to attain 10 kilowatts in the infrared-energy regime by summer's end, and subsequent resumption of full operations.
"It can be challenging pulling together all these threads," Dylla says. "There haven't been any major problems. We've had little ones, but nothing that we, along with help from our JLab colleagues and outside suppliers, haven't been able to overcome. We still have a lot of work to do before we get the machine up and performing optimally."
The "tuneability" of the upgraded FEL across a broad range of wavelengths, from infrared to ultraviolet, is of crucial importance for materials research, as it helps scientists better understand the behavior of particles at the atomic level and below. Its enhanced capability should also provide industrial uses of the FEL with a fast and cost-effective means of changing material properties, both on surfaces and in bulk.
"If we had stopped at one kilowatt, we would have had a very interesting machine," Dylla says. "But we wanted to make the machine even more useful. And we are."
Improvements began in September 2001 but will not be complete until the fall of 2004. The FEL also produces long wavelength light with a frequency in the range of trillions of cycles per second. This "terahertz" capacity could conceivably lead to imagers that could quickly detect biological agents, such as anthrax, and hunt for concealed land mines.
Among the FEL's enhanced capabilities is an ultraviolet-light (UV) one-kilowatt "sidecar" add-on. New experiments with the UV FEL will assess the nature and extent of the human health risk arising from increased exposure to ultraviolet light.
FEL research falls into three broad categories: photo-induced chemistry, biology and materials. FEL proof-of-concept experiments have included investigations of chemical-vapor deposition, a technique used to produce high-quality coatings and thin films for electronics and metals, as well as the effects of FEL processing on nylon, polyester and a class of materials known as polyimides, including altering the surface properties of food packaging, making it more resistant to microbes and food spoilage.
The Lab's FEL has also been able to create in quantity ultra-small but very strong structures known as carbon nanotubes, which could eventually be the heart of minuscule next-generation computers, as well as structural components for aircraft and automobiles. Areas under future investigation are expected to include the function of protein molecules within human cells, as well as the mechanisms that determine and degrade materials purity, such as the silicon that comprises many computer components. Scientists will also study the effects of new surface compounds, produced when metals bathed in nitrogen are exposed to FEL light, and explore novel areas such as "spintronics," which concerns the properties of next-generation semiconductor designs that optimize performance using the magnetic properties of materials.
The amount of FEL operational time in 2004, the first full year of operations, remains to be determined. Runtime will depend on when the machine comes fully on line, and on the demand from paying customers. Dylla expects that 40 percent of the new machine's time will be devoted to basic research conducted by universities and other national laboratories, with 40 percent derived from applied projects conducted on behalf of the private sector, and 20 percent emanating from a variety of Department of Defense projects.
"We all think the future of this FEL is a pretty good one," he says. "The team is very excited about seeing the machine come back on line for our existing and new users."
Materials provided by Thomas Jefferson National Accelerator Facility. Note: Content may be edited for style and length.
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