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Two SLAC Scientists Receive DOE Early Career Research Awards

Markus Guehr of the PULSE Institute for Ultrafast Energy Science, a joint SLAC/Stanford institute, and Faya Wang of SLAC's Accelerator Research Division are among 65 young researchers selected from a nationwide pool of more than a thousand hopefuls who will receive five-year grants for their research from the Department of Energy. The awards, announced early this month by the DOE Office of Science, are intended to provide support to promising young researchers at the beginning of their careers—often a time of little money but a lot of energy, enthusiasm and good ideas.

(Photo - Markus Guehr)
Markus Guehr.
(Photo courtesy Markus Guehr.)

Markus Guehr's good idea, selected by the DOE Office of Basic Energy Science, is an attempt to shed light—literally—on photochemistry, the study of how light energy affects interactions between the electrons of different atoms and between electrons and atomic nuclei within a molecule. Electron interaction is the basis of chemical bonding, Guehr explained, but as electrons rearrange themselves, atomic nuclei are affected as well.

"To understand chemistry you need to understand the valence electrons," the electronc responsible for bonding, Guehr said. Capturing the dynamics of bonding electrons requires monitoring the changes in their distribution over time, and how those changes affect the atomic nuclei. "But unfortunately," Guehr added, "electrons are very, very fast."

Guehr proposes using ultrashort light pulses in the extreme ultraviolet and soft X-ray ranges in conjunction with a technique known as time-resolved spectroscopy. To generate the ultrashort light pulses the experiment will need, Guehr intends to take advantage of a process called high harmonic generation, which can convert a wavelength of light to a related, shorter, more energetic wavelength called a harmonic. Guehr said he is also excited about using ultrafast soft X-ray pulses from SLAC's Linac Coherent Light Source to shed light on molecular electronic dynamics.

Guehr and his colleagues will excite a sample material with a pulse of light, then probe the sample using pulses of extreme ultraviolet or soft X-ray photons to see how the electron properties within the excited sample change over time.

The results will enable a better understanding of, and possibly control of, light-driven chemical reactions at the level of electrons, according to Guehr. The ability to harvest the energy in light is at the core of sustainable energy advances such as artificial photosynthesis, a priority of the DOE.

"I want to thank my collaborators in PULSE," Guehr said. "I got a lot of good feedback from them, a lot of good comments—and before that, a lot of good collaboration."

(Photo - Faya Wang)
Faya Wang.
(Photo by Lori Ann White.)

Faya Wang will receive funding from the Office of High Energy Physics for another good idea, an experiment that could lead to shorter, less expensive linear accelerators for use in a variety of applications such as linear colliders, compact light sources for imaging studies in medicine, environmental sciences and many other areas—even fusion.

The key to these advances is finding ways to accelerate particles to much higher energies, over much shorter distances. However, the energies involved can themselves affect the accelerator, damaging it to the extent that the radio frequency field used to accelerate the particles can no longer propagate. This is called RF breakdown.

"Based on innumerable experiments, electric fields, magnetic fields and pulsed heating [cyclic stress of the interior surface of an accelerator cavity due to repeated heating and cooling] are thought to affect RF breakdown," Wang explained. However, he added, since all three phenomena exist in tandem in an accelerator cavity, it's not clear what role each plays. Wang intends to find out just that by designing a special accelerator cavity in which he can control each of the destructive elements separately. In addition, he intends to induce the pulsed heating effect using a laser in the cavity, an experimental first that will enable even finer control.

"A good understanding of these effects is important for designing structures capable of supporting high accelerating gradients—beyond the current state of the art—and devices such as klystrons and magnetrons used to generate very high peak, yet reliable RF power for driving accelerators," Wang said.

Wang, too, thanks his colleagues. "I worked with [supervisor] Chris Adolphsen and several other colleagues. I got a lot of help from them," Wang said. Even with the excellent support, he said he "was very surprised to be chosen."

Adolphsen isn't so surprised. "Faya is very creative and he's got a lot of good ideas," he said. "It's good that he's been recognized as being capable of carrying this off."

—Lori Ann White
SLAC Today, May 18, 2011