With the power of 10 nuclear power plants, a laser beam strikes. For an instant, a ten billionth of a second, the human-hair-thin wafers of plastic and silicon become so hot and dense that standard descriptions of matter don't cut it and measurements of temperature become theoretical.
In walks Adrien Descamps, a postdoctoral fellow working with Emma McBride in the Centre for Light Matter Interaction at Queen's University Belfast, peering at the experimental enclosure covered in silicon particles that "are everywhere except where they were initially."
Descamps, a former graduate student in the High Energy Density Science division at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University, is taking the first direct temperature measurements of materials in this extreme state, rather mildly called " warm dense matter ." Those measurements have broad applications, including the study of planets' interiors and the development of fusion energy here on Earth.
Now, for his work turning SLAC's Linac Coherent Light Source (LCLS) into what he calls "a billion-dollar thermometer," the LCLS User Executive Committee (UEC) has awarded Descamps its 2024 LCLS Young Investigator Award . The winner of this award is selected by the international team of scientists that makes up the UEC, drawing from a list of candidates submitted by the whole community in an open call each year, ranging from the biosciences to a broad range of materials and chemical sciences.
This recognition from his peers means a lot, Descamps said. The nonscientists in his life don't always understand why he's devoted years to blowing things up with one laser and measuring the results with another laser.
"Being actually recognized for all the effort feels special," Descamps said, especially when the recognition comes from "other people who also do very exciting things."
Warm, dense and a bit frustrating
Descamps originally got interested in measuring temperature at SLAC, where he learned that scientists know more about other planets than Earth's own core. "It's all open questions as to what is happening in there," he said.
He found temperature especially interesting because it is deceptively difficult to measure. Knowing so little about such a familiar concept was "a bit frustrating." Even with a billion-dollar thermometer, measuring the temperature of warm dense matter is challenging. Physical thermometers operate too slowly and light used in conventional spectroscopy can't penetrate deep enough to determine temperatures inside a warm dense plasma.
Scientists instead often rely on predictive models that take observations of a material at certain temperatures, densities and pressures and predict that material's properties as those variables change. But the properties of warm dense matter are so extreme that, like predicting the shape of a continent based on a short stretch of coastline, it's uncertain whether the extrapolation will work.
If the models are wrong, "then you have lost all predictive capabilities," Descamps said, "and this can be problematic when you are trying to make fusion happen."
That means these models need to be benchmarked against new observations of materials at extreme conditions if they are to be trusted.
The world's most powerful thermometer
To solve this problem, Descamps is using LCLS as a spectroscopic thermometer to measure temperatures in warm dense matter. First, Descamps and his colleagues shot a laser at samples of polyimide, a kind of plastic, and silicon using the Matter in Extreme Conditions instrument at SLAC. Then, they fired superfast X-ray pulses from LCLS, the world's most powerful X-ray laser, at the warm dense matter that resulted. By measuring the shift in energy of the X-ray pulses - which have enough energy to pass through the warm dense matter and out the other side - Descamps can calculate the temperature directly.
"This technique leverages that you don't need to assume anything about the behavior of the material - you get the information directly from it," Descamps said.
To get the most accurate measurements, he first bounces the LCLS beam off two monochromators, focusing the beam into a super narrow energy range.
After the beam's photons reach their target and scatter, they are received by three diced silicon analyzers designed by Descamps and researchers at SLAC and the European Synchotron Radiation Facility. The analyzers separate out the different wavelengths that compose X-rays, providing even more granular detail - like a prism splitting white light into a rainbow, Descamps explained.
Siegfried Glenzer, division director for High Energy Density Science at SLAC and Descamps's former graduate supervisor, said that his former student's laser-like focus is what makes Descamps such an effective researcher. "He's really systematic about his approach, so he understood what needs to happen."
Descamps identified the expertise of potential collaborators, the technology and techniques that needed to be developed, and the companies that could actualize the designs, Glenzer said. He slogged through theory and predictions, testing hypotheses on simpler experiments. Finally, he tied it all together into groundbreaking measurements.
Descamps has his sights on measuring more complex systems. His next goal is measuring how warm dense matter moves around when mixed together - an important feature when modeling the Earth's core.
Descamps's contribution is the result of seven years of research into warm dense matter, with colleagues at SLAC and around the globe.
"I love it, but it also takes a lot," Descamps said. "And I think everyone deserves some sort of an award for doing the work."
LCLS is an Office of Science user facility.
