EXPERIMENTALLY MEASURING THERMAL CONDUCTIVITY IN WARM DENSE MATTER USING FRESNEL DIFFRACTIVE RADIOGRAPHY

Transport properties play a vital role in understanding how a material interactsand evolves in larger systems, quantifying how microscopic processes involving the transfer of heat, mass, and momentum between particles can influence macroscopic observables that we interact with daily. In particular, the thermal conductivity, κ, of a given material characterizes how quickly heat flows through it. In daily life, it most often appears in terms of insulating against hot and cold, examples including what cup to use for coffee, what form of insulation to use in walls, and much more. In these mundane situations, the material thermal conductivity is well characterized and easily tested. However, for materials at more rarely-encountered, extreme conditions, the thermal conductivities are less well known, and for conditions known as warm dense matter - found most commonly inside large planets and dwarf stars - we require experimental benchmarking to ensure accurate theoretical and computational work in this regime. This dissertation details the development of the Fresnel Diffractive Radiography platform, which uses X-ray interference effects - refraction and diffraction - to determine the sub-micron evolutions in density gradients at warm dense matter interfaces. These evolutions are a response to heat flowing across the interface and are used to determine the rate of thermal conduction in the constituent materials. This is made possible through the use of novel 1 μm-wide slits that create a partially spatially coherent, high-resolution X-ray source, capable of resolving both refraction features- as a result of X-rays passing through different materials - and more significantly, diffraction features - resulting from sharp density gradients in the system. A series of experiments were performed at the Omega Laser Facility to first develop and then utilize Fresnel Diffractive Radiography. By imaging the dynamic evolution of an interface between warm dense tungsten (W) and parylene (C8H4F4, 'CHF'), we obtain high spatial resolution (∼ 2 μm) diffraction patterns of the evolving interface at multiple times. The characteristic density profile for these diffraction patterns is found at each time, and by simulating heat flow through the system defined by these profiles, we obtain thermal conductivities that are consistent with previously published literature at warm dense conditions (κW = 97.6 W/m/K, κCHF = 170.3 W/m/K). Additionally, future experiments at the Omega Laser Facility and the National Ignition Facility are detailed. These campaigns use Fresnel Diffractive Radiography to measure multiple transport properties for a broader set of materials, including those that have applications to planetary science, such as nickel and iron, and to inertial confinement fusion, such as deuterium.

Level thesis:degree_level

Doctorate Degree

Year dc:date.issued

2023

Author dc:creator

• Allen, Cameron

Advisor dc:contributor.advisor

• White, Thomas G

Committee members dc:contributor.committeemember

• Doeppner, Tilo
• Safronova, Alla
• Plotkin, Richard
• Aureli, Matteo

• diffraction
• radiography
• thermal conductivity
• warm dense matter

Statement dc:rights

• Creative Commons Attribution 4.0 United States

Handle dc:identifier.uri

http://hdl.handle.net/11714/10632

OAI identifier oai:identifier

oai:scholarwolf.unr.edu:11714/10632