By Saren Johnston
At last, MUCAT has seen the light!
After 10 years of planning and construction, and a whole lot of problem-solving, the undulator beam line developed by the Midwest Universities Collaborative Access Team is up and running at Argonne National Laboratory's Advanced Photon Source near Chicago.
"The beam line is operational. We're actually at the point where we're taking data, getting results and writing papers," says Alan Goldman, an Ames Laboratory senior physicist and chair of the Iowa State University physics and astronomy department. He heads MUCAT, a group of scientists from eight universities and one German institute that was organized in 1990 to develop a sector at the APS.
The APS provides MUCAT scientists and members of other collaborative access teams with a means of tapping into some of the strongest X-ray beams in the world. Goldman and his MUCAT colleagues can use the brilliant, highly focused X-rays produced by the APS third-generation synchrotron radiation source to investigate the molecular make-up of all kinds of materials, ranging from magnets, ceramics and soils to proteins, drugs and asteroid dust.
"The APS is an incredibly versatile tool that allows you to see microscopic details of materials with extremely high resolution," says Goldman. "It can be used by almost any group interested in looking at the structure of materials. Most significantly, because it has wide applications to so many fields, it allows for collaborative research efforts among different disciplines."
The APS synchrotron operates round-the-clock, generating electrons and accelerating them to energies approaching the speed of light. In just a quarter of a second, the electrons can make 200,000 trips around the synchrotron's 368-meter circumference (approximately 405 yards) as they climb to energies approaching 7 billion electron volts.
From the synchrotron, the electrons are injected into a giant storage ring about two-thirds of a mile in circumference. The storage ring is constructed as a set of curves connected by straight sections. Once inside, the electrons travel in a concentrated beam, circling the ring more than 271,000 times per second. The electron beam is guided and focused by hundreds of powerful electromagnets that keep it moving in a circular path.
Researchers have optimum access to the beam through the experiment hall, which surrounds and is separated from the storage ring by a shielding wall. The experiment hall consists of 35 sectors, which serve as laboratory space for the collaborative access teams using the APS.
"Each sector in the APS really consists of two beam lines that tap the synchrotron radiation produced by the storage ring's electron beam," says Goldman. "The insertion device beam line contains powerful permanent magnets that have been placed in the straight sections of the storage ring to either wiggle the beam back and forth or make it undulate -- this is how you get synchrotron radiation. But the act of turning the beam around the corner by a bending magnet will also produce synchrotron radiation, so each sector also has a bending magnet beam line," he explains.
The bends, wiggles and undulations produced by the bending magnets and insertion devices alter the electron beamÕs course and allow it to navigate the straightaways and curves of the storage ring. As its path changes, the beam sheds synchrotron radiation in the form of X-rays that range in power from 1 kilovolt to hundreds of kilovolts. By way of comparison, Goldman says that standard medical X-rays have an energy of 50-60 kilovolts.
Although the undulator beam line in MUCAT's sector 6 is now working, Goldman says it's difficult to pinpoint the exact date it became operational.
"There's a constant effort in commissioning that goes on when you're getting beam. And there are lots of problems to solve on these lines because they're extraordinarily complicated," he says.
Fortunately for Goldman and the rest of the MUCAT scientists, they have an outstanding group of trouble-shooters to count on. Doug Robinson, an Ames Lab physicist, is in charge of operations at the beam line. "More than anyone, Doug has really made that thing work," says Goldman.
He adds that Ames Lab assistant scientist Eric Zoellner has been at the beam line since the beginning of construction. "Eric has had an awful lot to do with its success, as has Didier Wermeille, a postdoc in my group who's been working on the beam line for about two years."
The building process for sector 6 started from the ground up, or put more accurately, from the wall out. "What the APS gives you in the very beginning is a hole in the wall," says Goldman with a grin. "Basically, what you get to start with is a beam pipe and a flange at the end. You have to build everything else outside to access the storage ring's electron beam."
Everything else includes a lot of expensive equipment, so sector 6 is coming together bit by costly bit. There's an enclosure for the optical systems that condition the X-ray beam so researchers can use it in the experimental station. "All of the instruments and equipment in the optics enclosure condition the beam so we get something clean coming down the pipe and into the experimental enclosure, which is about 50 meters from the storage ring," explains Goldman.
The MUCAT undulator beam line consists of two experimental stations that operate in tandem. And those stations are slowly filling up with the kinds of equipment that will allow Goldman and other MUCAT members to carry on a diverse assortment of research projects. An instrument currently in operation in station 1 is the four-circle diffractometer.
Goldman and his Ames Lab colleagues are using the diffractometer to perform magnetic scattering measurements and to study X-ray diffraction from single crystal samples produced at the Lab. The work has brought new information to light about the magnetic structures of the compounds from which the crystals were produced, as well as revealed new magnetic transitions that did not show up under traditional measurements.
Station 1 is also the home of a novel piece of equipment that is one of only a few in the world. The liquid surface reflectometer developed by Ames Lab physicist David Vaknin will be used in conjunction with the powerful APS X-rays to investigate the structure of ultrathin layers of organic materials that may one day be used in novel optical, electronic and biological devices.
A piece of equipment being tested in station 1 on the MUCAT undulator beam line is a new compact furnace designed by Goldman and Ames Lab researchers Bill McCallum, Matt Kramer, Kevin Dennis and Larry Margulies (see furnace story). The furnace allows high-temperature powder diffraction studies of complex materials at various temperatures and under the same processing conditions that exist in the laboratory environment. The resulting diffraction patterns reveal what happens to the crystal structure as a material heats and cools, information needed to better understand and control the microstructure of new materials.
"I expect the new compact furnace will be one of the most popular instruments on the beam line because it's really rather unique," says Goldman. He explains that the idea was to scale down a basic tube furnace design and make it fit on the four-circle diffractometer to take advantage of the high-energy X-rays produced by synchrotron radiation.
"You can control the furnace temperature up to 1,500 C (2,732 F) and also spin the sample in such a way that there are no preferred orientation effects. It's worked quite nicely," he adds.
In addition to the equipment already in place, researchers in sector 6 will soon be able to make use of a new surface science chamber. Funded by the National Science Foundation, the chamber will be constructed in station 2 on the MUCAT undulator beam line. It will be used to study the surface properties of materials and surfaces that are grown in situ using a variety of techniques.
"There's a lot to do, but it's going to be fun," says Goldman. "I like playing with complicated pieces of equipment. And I like seeing things come together and work."
With any luck, Goldman will see that happen with the special high-energy side station, which is being funded and constructed by the German institute, F. Z. Juelich, a MUCAT member organization. As its name implies, the high-energy side station will sit to the side of the main undulator beam line in sector 6. It will operate in parallel with the beam line, supplying energies up to 120 kilovolts compared with the main beam line's lower energies of 3-40 kilovolts.
"The high-energy range is for experiments in which we want to penetrate into the sample more deeply," says Goldman. "The low-energy range will help us with magnetic scattering studies on actinide materials."
Goldman and his colleagues have a lot on their plates, but not so much that they can't make room for more, especially when it comes in the form of a second beam line for sector 6. "We've been funded to build a bending magnet beam line, which will complement the undulator line and allow a wide variety of standard scattering and spectroscopy techniques to be used," Goldman says. "This is where the high-temperature diffractometer and the compact furnace will live, eventually."
Experiments planned for the bending magnet beam line include studies of phase diagrams, in situ investigations of nucleation and growth, recrystal-lization of bulk metallic glasses and processing of high-temperature materials.
Getting the new beam line operational will mean a lot of travel between Ames and Argonne for Goldman, who never seems to worry about the time or the miles. "I think one of the things that keeps me going is that there's this instant in time when you're working on a project and you finally understand, or think you have a good way of understanding, what's going on in a material," he says. "And for that instant, you know something that other people don't know. So it's just discovery itself."
And in the end, discovery is the reason Ames Laboratory has strongly supported the MUCAT project, beginning with the 1990 initial planning stages -- before the APS was even built. "The Lab's support over the years has been just outstanding," says Goldman. "The APS is a remarkable tool for synchrotron X-ray studies for the general scientific community. And we're going to welcome anyone to come out and do some work."
For more information:
Alan Goldman, (515) 294-5441
goldman@ameslab.gov
Research funded by:
DOE Office of Basic Energy Sciences
Last revision: 9/15/00 sd
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