The Advanced Photon Source—-so large that it can encircle a baseball stadium is located in the southwest corner of the laboratory.

University of Chicago researchers used the GeoSoilEnviroCARS earth science research facility at the APS to produce temperature and pressure conditions close to those at the center of the Earth. GeoSoilEnviroCARS Associate Director Mark Rivers works in the high-pressure lab.

APS advances frontiers in many fields

The Advanced Photon Source already produces the nation's most brilliant X-ray beams for research, but Argonne scientists and engineers continue to make it even better.

The APS’ brilliant X-rays are used by scientists from around the world to examine materials in greater detail than before. Researchers can watch atomic and molecular activity as it occurs. The facility, funded by the U.S. Department of Energy's Office of Basic Energy Sciences, has opened new doors for scientists in many fields.

The 1,104-meter circumference APS, large enough to encircle a baseball stadium, houses a complex of machines and devices that produce, accelerate and store a beam of electrons that is the source of APS X-ray beams.

The APS is a unique partnership between government, academia and industry. The Department of Energy provides the operating budget. The University of Chicago operates APS and Argonne for DOE. Academic and industrial partners build the beamlines, using funds from government and private sources.

Users who perform the experiments come from universities, labs and companies across the United States and around the world. And finally, the facility involves partnerships between accelerator physicists and users interested in X-ray physics, chemistry, materials science, geosciences, biology and environmental science.

During fiscal year 2002, the primary operating mode at the APS has been “top-up.” This new method of accelerator operation maintains a constant level of current in the storage ring. Top-up operation also maintains constant heat load on X-ray optics and storage ring components, constant power demands on radio frequency generators, and sends a constant signal strength to beam-position monitors, lengthening the lifetime of technical components.

Using top-up operating mode increases beam stability, which is especially advantageous for experiments on very small samples. It also permits low-emittance operation, which results in a smaller beam “spot size”—important for microbeam research such as microprobe and microdiffraction, and greater coherence—important for techniques such as correlation spectroscopy and X-ray imaging.

Another new APS operating accomplishment is a way to extract two separate X-ray beams from a single straight section in the accelerator, effectively doubling the number of experiments that can be performed simultaneously on a beamline. This is particularly important in the field of macromolecular crystallography. The APS macromolecular crystallography facility solves the structures of large crystals more quickly than anywhere else.

The extraction of two beams was accomplished through the development of the canted insertion device, which places two insertion devices at a small angle with respect to each other. Insertion devices—linear arrays of magnets alternating in field direction—vibrate the electron beam, causing it to emit photons at a certain energy each time the beam is bent back and forth, thereby increasing the brilliance of the X-rays produced. Using the canted device increases the versatility of the X-rays as well.

The APS was the site of many exciting discoveries in 2002.

Examining anthrax
Researchers from the University of Chicago’s Ben May Institute for Cancer Research and the Boston Biomedical Research Institute described the 3-D structure of edema factor, one of three toxins that make anthrax so deadly. This finding, published in Nature, is a crucial step toward designing drugs to block the harmful effects of anthrax and perhaps other bacterial toxins.

The edema factor is harmless when it first enters a cell. But if it interacts with calmodulin, a common protein found in most cells, the toxin is prompted to slide apart. The calmodulin settles into the toxin and changes its shape. The altered edema factor toxin over-stimulates cells, and water leaks out, causing surrounding tissue to swell and die.

The researchers determined the structure of edema factor by crystallizing it and X-raying it in the APS. 

Edema factor’s structure may leave it vulnerable to new drugs. The protein contains a deep pocket, essential to its destructive action, which could be plugged by a small molecule. Because edema factor is so different in shape from its benign chemical cousins, scientists may be able to find antibodies that selectively seek out and neutralize the bad protein.

Finding new semiconductors
Researchers are using the APS to search for new materials for solid state cooling and power generation applications requiring portability or long-term reliability. Examples of this sort of specialized need range from cooling individual electronic components or powering a space probe to Saturn.

Semiconductors with a particular crystal structure, type 1 clathrate hydrate, have potential for such applications due to their unusual physical properties—low resistance, low thermal conductivity and the ability of each charge carrier passing through the device to transport a large amount of heat.

Researchers have predicted that a material combining the low thermal properties of glass with charge carrier mobilities found in crystalline materials would be ideal, leading to the preparation of crystalline framework materials with atoms capable of transporting heat held inside cavities in the framework.

Researchers from the Georgia Institute of Technology, the University of South Florida and Argonne used the APS’ X-rays to count the electrons in the atoms of similar molecules of these materials. They are close structural relatives of gas hydrates, which have a hydrogen-bonded network of water molecules forming a framework around the small gas molecules. Understanding this framework may enhance thermoelectric performance.

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