What is HP-CAT?

By Daniel Häusermann, HP-CAT Project Manager

Inside the first beamline enclosure, the double-crystal monochromator (in the foreground, open, and showing the “cage,” which holds the crystals) is the key instrument used to select the X-ray beam for spectroscopy experiments. Behind it is the high-heat-load beam-defining slits and in the far back is the differential pumping unit, which isolates the beamline from the storage ring vacuum.

The Geophysical Laboratory’s (GL) high-pressure team investigates how materials react and change under high pressure and varying temperatures. It has discovered new materials and new physical properties through its research, and it has advanced our understanding of what happens in highly compressed, hot planetary interiors. To obtain the highest pressures and temperatures possible and to examine what happens to materials under extreme conditions, GL has joined forces with two other institutions to form HP-CAT—the High Pressure Collaborative Access Team. Carnegie manages the project, which includes participants from the High-Pressure Physics Group of the Lawrence Livermore National Laboratory, and the High Pressure Science and Engineering Center of the University of Nevada, Las Vegas. The consortium is building an integrated high-pressure facility at the Advanced Photon Source (APS), at Argonne National Laboratory in Illinois. The new installation will unleash the full potential of high-pressure methods for physics, chemistry, and materials science.

The APS is a 7 giga-electron-volt third-generation synchrotron radiation source. It is a huge storage ring with a circumference of 0.7 mile in which a tiny beam of positrons—focused down to the size of a human hair—travels at the speed of light between the poles of magnetic lattices. This produces ultrabrilliant laserlike beams of X-rays millions of times brighter than those emitted by conventional laboratory X-ray sources.

The new research facility will advance high-pressure science by allowing new types of experiments to be performed including complete crystallographic studies of materials at multimegabar pressures; measurements of the dynamics of electrons, atoms, and nuclei; and detailed studies of complex materials as functions of pressure, temperature, and time. In addition, new-generation high-pressure devices such as large-volume diamond-anvil cells

will all be exploited. Researchers will be able to study local chemical environments, including atomic coordination, structures, and bonding character, with a wide variety of X-ray spectroscopies.

Thus far, high-pressure X-ray spectroscopy has been hindered by insufficient synchrotron radiation intensity and by the opaqueness of high-pressure vessels at crucial X-ray energies. With the dramatic improvements in X-ray intensity and X-ray transparent ultra-high-pressure cell components, the new facility opens a window on a previously forbidden energy range. The ultimate goal of HP-CAT is to advance high-pressure synchrotron radiation research to set up a world-leading high-pressure research center accessible to the scientific community at large.

The Geophysical Laboratory’s HP-CAT team is stationed permanently at the APS, and is currently designing and constructing the installation with the support of an engineering design team based in Manchester, England (Instrument Design Technology). The construction of the nine lead enclosures, which will house the optics and experimentation, started in 2001 and will be completed by the end of May on a 12-hours, six-days-a-week work schedule.

Radiation tests were carried out on the first two enclosures and their X-ray beam transfer line in November and December 2001, and the installation of instruments started in January. High-heat-load beam-defining slits and the double-crystal monochromator are now in place and ready to be tested. The rest of the instrumentation required to deliver beam to the second enclosure will be installed in June 2002, and microdiffraction commissioning experiments are planned for this summer. One other experiment station will be commissioned every three months until the full five stations become operational by the spring of 2003.

previous | table of contents | next