Novel Intermediate Energy X-ray Beamline Opening for Researchers

Estimated reading time: 8 minutes

Like the formation of a new particle in a collider, it was the research trajectory of two scientists that forged the foundations for IEX beamline. Physicists Juan Carlos Campuzano of the University of Illinois at Chicago (UIC) and Peter Abbamonte of the University of Illinois in Urbana Champaign (UIUC) both studied the complicated dynamics of high-temperature superconducting materials.

By 1985, Campuzano had already proposed a similar, but less advanced, beamline at the Swiss Light Source, in Villingen, Switzerland, while Abbamonte, as a postdoc, had been on the team that pioneered the RSXS endstation, at Brookhaven National Laboratory in Upton, NY. Eventually, both took jobs within the University of Illinois system and were seeking an intermediate energy X-ray source in the Midwest to conduct their research.

Given the challenges presented by these superconducting materials, they decided a better, brighter beamline was in order. They wrote a proposal that garnered funding from the National Science Foundation (NSF), which suggested they build the instrument at the newly established APS at Argonne, where Campuzano held a joint appointment.

They reached out to APS beamline scientist George Srajer, now deputy associate laboratory director for Photon Sciences, to forge a partnership with DOE to fine-tune the concept and secure the remaining funding. A beamline was born.

"So there was this freak convergence of a lot of different things: the right combination of science, geography, and technology all at the same time," said Abbamonte, now professor of physics at UIUC.

Making the beamline unique

With several similar beamlines in Japan and Europe already operating, the toughest challenge in requesting funds for and building the new IEX beamline at the APS was to create something unique, noted Campuzano.

"And it doesn't seem like a big deal, but deciding what not to do was very important," added Abbamonte. "You build a $15 million machine and people want to make it do everything. But that ends up costing more and the experiment that is supposed to do everything ends up doing nothing, because the more versatile an instrument is the more difficult it is to make it work. So we decided to focus and pick a few really important things."

A key feature unique to IEX at the APS is the beamline's insertion device (ID), the magnetic system responsible for shaping the properties of X-rays provided to the beamline.

According to Srajer, there is no other like it in the world.

The ID is an electromagnetic variable polarizing undulator (EMVPU), operating in a range of 250 to 2,500 electron volts (eV). Like a fixed magnet device, users can change the energy of the X-rays and polarization at the sample. But the new ID also allows the source to run in quasi-periodic mode, which suppresses the higher harmonics in the X-ray beamline, resulting in a much higher signal-to-noise ratio that is ideal for detecting small signals in a large background.

One advantage to developing a lower-energy beamline at a high-energy storage ring is that the intensity produced by the undulator is rather flat across the whole 250- to 2500-eV energy range. This minimizes the need for normalization, unlike at lower-energy storage rings where users must switch between the different undulator harmonics.

To accurately deliver the X-rays produced by the ID to the endstations required the complicated design and manufacturing of X-ray optics that precisely adjust X-ray parameters, such as focus, energy resolution, and coherence fraction. Users can further tailor the X-ray beam for a given experiment by selecting between one of three gratings in the monochromator, optimizing the total intensity or flux (109–1012 photons per second) and energy resolution (5–300 milli-electron volts [meV]).

Page 2 of 3

• < Previous Page
• Next Page >