First Beam:
HPCAT Gets Closer
to Science with Innovations Galore
“These advances will make the facility the best and most flexible in the world for high-pressure/ temperature experimentation.”
The High Pressure
Collaborative Access Team (HPCAT) is located at the Advanced Photon
Source (APS) at Argonne National Laboratory in Argonne, Illinois. Shown
far left is the APS synchrotron. The HPCAT sector is located at approximately
12 o’clock.
Image courtesy Argonne National Laboratory
Why Synchrotrons?
During the 1990s, three third-generation synchrotron facilities came on line: the European Synchrotron Radiation Facility in France, SPring-8 in Japan, and APS at Argonne National Laboratory in the U.S. The APS is a circular particle storage ring, which produces short-wavelength, or “hard,” X-rays when high-energy positrons (the positively charged antiparticles of the electrons) are accelerated inside an injection system and then forced along a curved trajectory in the storage ring. Each 10-degree portion, or sector, of the 0.7-mile synchrotron ring consists of two bending magnets and two straight sections where X-rays are produced by accelerating the positrons in intense magnetic fields. These X-rays shine at a tangent to the central circle and feed “beam lines,”where the research is performed.Most sectors are built for a specific kind of research on materials. The short-wavelength X-rays are comparable in size to the distances between atoms and can therefore be used to determine the minute structures and other properties of a vast array of substances, from viruses to nuclear materials. Collaborative Access Teams (CATs) at the APS study everything from molecular biology to fundamental physics and planetary science.Each research sector around the ring consists of an arrangement of lead “enclosures,” or hutches. Some house the optics required to harness the X-rays while others, the experiment enclosures, contain a range of sophisticated, and often custom-designed, remote-controlled equipment used for research. The high-intensity, sharply focused X-rays at the APS are effectively superbrilliant laserlike beams, which are 10,000 times brighter than those available at previous-generation facilities. The advancement in beam quality allows X-ray diffraction—the scattering pattern that can reveal the atomic structure of a crystal—of much smaller samples than before. For high-pressure work, researchers will be able to make much finer measurements of materials to well above 300 gigapascals, which is equivalent to the pressure at the center of the Earth, and to temperatures exceeding 6000 K. A host of spectroscopic devices can also be used to identify specific atoms in a sample. And the ability of the APS to pulse the beam at intervals of 20 trillionths of a second will allow investigators to provoke and view atomic vibrations and displacements in samples in real time.
High-pressure researchers will be able to use the APS to measure crystal and liquid structures, the transitions of materials from one phase to another, melting, vibrational dynamics, elasticity, plasticity, texture development, bonding, electronic and magnetic structures, [continued on page 9]