researchers working at the lawrence livermore national laboratory (llnl) in livermore, calif. have developed an experimental platform, called differential heating, to measure the thermal conductivity of materials in the warm dense matter (wdm) regime, which had previously been limited to theoretical models.

inside the titan laser target area, from left, jim king (ohio state university), andrew
mckelvey (university of michigan), rui hua (ucsd), and yuan ping (llnl). 
(lawrence livermore national laboratory)

scientists used the titan laser at the llbl jupiter laser facility, according to a report on the llnl website, to get the first measurements of warm dense aluminum by heating a dual-layer target of gold and aluminum with laser-generated protons. the experiment produced simultaneous data from the hotter gold and the colder aluminum.

“by comparing the data with simulations using five existing thermal conductivity models, the team found that only two agree with the data,” the article explained. “the most commonly used model in wdm, called the lee-more model, did not agree with data.”

the researchers, who are from a series of universities across the u.s., plan to continue using the laser and this experimental setup to test iron and carbon.

the research was recently published in scientific reports. the abstract stated:

“thermal conductivity is one of the most crucial physical properties of matter when it comes to understanding heat transport, hydrodynamic evolution, and energy balance in systems ranging from astrophysical objects to fusion plasmas. in the warm dense matter regime, experimental data are very scarce so that many theoretical models remain untested.

“here we present the first thermal conductivity measurements of aluminum at 0.5–2.7 g/cc and 2–10 ev, using a recently developed platform of differential heating. a temperature gradient is induced in a au/al dual-layer target by proton heating, and subsequent heat flow from the hotter au to the al rear surface is detected by two simultaneous time-resolved diagnostics.

“a systematic data set allows for constraining both thermal conductivity and equation-of-state models. simulations using purgatorio model or sesame s27314 for al thermal conductivity and leos for au/al release equation-of-state show good agreement with data after 15 ps.

“discrepancy still exists at early time 0–15 ps, likely due to non-equilibrium conditions.”