Thermal Property Characterization, Modeling, and Theory in Extreme Environments: Thermal Transport Theory & Mechanisms
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Janelle Wharry, Purdue University; Mukesh Bachhav, Idaho National Laboratory; Marat Khafizov, Ohio State University; Eric Lass, University of Tennessee-Knoxville; Vikas Tomar, Purdue University; Tiankai Yao, Idaho National Laboratory; Cody Dennett, Commonwealth Fusion Systems; Karim Ahmed, Texas A&M University
Wednesday 2:00 PM
March 17, 2021
Room: RM 53
Location: TMS2021 Virtual
Session Chair: Vikas Tomar, Purdue University; Mukesh Bachhav, Idaho National Laboratory; Karim Ahmed, Texas A&M University
2:00 PM Invited
Thermal Transport in Irradiated ThO2: A Combined Experimental and Phonon Level Investigation: Anter El-Azab1; Walter Deskins1; Maniesha Singh1; Sanjoy Mazumder1; Kumagai Tomohisa1; Jie Peng1; Marat Khafizov2; Zilong Hua3; Lingfeng He3; David Hurley3; 1Purdue University; 2Ohio State University; 3Idaho National Laboratory
We present a theory driven program for predicting thermal transport in irradiated ThO2, where computational models and experiments are combined to make progress. A Boltzmann Transport Equation (BTE) approach is used to model phonon transport and interactions at the mesoscale, with input consisting of phonon dispersion relations obtained by inelastic neutron scattering measurements and strain-based models for phonon scattering by lattice defects and microstructural features. Within a Monte Carlo (MC) solution scheme, point defects are represented as continuous fields that scatter phonons everywhere in the crystal while extended defects such as dislocation loops and voids are expressed as discrete strain sources that scatter phonons in a non-uniform fashion. MC simulations of phonon transport in irradiated ThO2 are compared with Modulated Thermoreflectance measurements of conductivity in the same material. This work is performed as part of the EFRC Center for Thermal Energy Transport under Irradiation.
2:30 PM Invited
Thermal Conductivity and Heat Transport Processes of Ion Irradiated and Laser Heated Solids: Patrick Hopkins1; Thomas Pfeifer1; Ethan Scott1; John Gaskins1; David Olson1; Khalid Hattar2; Mark Goorsky3; 1University of Virginia; 2Sandia National Labs; 3UCLA
The defects, temperature gradients and phase changes that can occur during ion irradiation and intense laser heating of solids can give rise to spatial gradients of varying thermal processes that push the extremes of thermal conduction in materials. In this work, we present a series of works in which we use a recently-developed steady-state thermoreflectance technique (SSTR) to characterize the thermal conductivity of materials after ion irradiation or during intense laser heating. We will discuss: i) thermal boundary conductance across GaN interfaces, and how ion irradiation can lead to increases in phonon heat conduction; ii) profiling the thermal conductivity of ion irradiated diamond as a function of depth under the surface through the end of range; and iii) measuring the thermal conductivity of intensely laser heated materials with temperature gradients on the order of 100’s of degree’s per micron, including molten salt materials of interest to next generation reactor technologies.
3:00 PM
Thermal Gradient Effect on the Transport Properties of Helium and Intrinsic Defects in Tungsten: Enrique Martinez Saez1; Nithin Mathew1; Danny Perez1; Dimitrios Maroudas2; Brian Wirth3; 1Los Alamos National Laboratory; 2University of Massachusetts; 3University of Tennessee
Plasma-facing materials (PFMs) in a fusion reactor are expected to withstand high heat and particle fluxes. These fluxes will create strong gradients of temperature and concentration of diverse species. Intrinsic defects and He atoms will then migrate in the presence of such gradients. We have used nonequilibrium molecular dynamics to study the transport properties of He, and self-interstitials in the presence of a thermal gradient in tungsten. We observe that defects and impurity atoms tend to migrate toward the hot regions of the material. The resulting concentration profiles are in agreement with the predictions of irreversible thermodynamics. We compute a negative heat of transport, which indicates that the respective driven species fluxes are directed opposite to the heat flux. These results have important implications for PFMs in fusion environments, mostly when abnormal operation occurs in the plasma, which increases the heat flux towards the material and intensifies the thermal gradients.
3:20 PM Invited
Phonon Transport in ThO2 from Neutron Scattering and First-principles Computation: Michael Manley1; Matthew Bryan1; Chris Marianetti2; Lyuwen Fu2; Krzystof Gofryk3; 1Oak Ridge National Laboratory; 2Columbia University; 3Idaho National Laboratory
We are investigating the microscopic origin of thermal transport in advanced oxide nuclear fuels, including thorium dioxide, using inelastic neutron scattering and first-principles calculations. Neutron scattering measurements performed on large single crystals provide a direct measure of the phonon group velocities and lifetimes controlling lattice thermal transport. These quantities enable us to deduce mode specific contributions to thermal transport. Since the phonon scattering processes responsible for lifetime broadening involve anharmonic interactions between multiple branches, a full accounting requires accurate calculations. Density functional theory (DFT) captures the phonon dispersion curves of ThO2 and allows calculations of the anharmonic terms from which phonon lifetimes are derived. The results of these calculations are benchmarked against the inelastic neutron scattering phonon dispersion and linewidth/lifetime measurements as well as thermal transport measurements.
3:50 PM Invited
Theory of Non-equilibrium Thermal Transport at High Temperatures from First-principles: Keivan Esfarjani1; 1University of Virginia
In systems of small dimensions or near interfaces subject to a thermal gradient, heat carriers are not at equilibrium. Such situations are traditionally modeled using non-equilibrium molecular dynamics simulations. In this numerical approach, a temperature is associated to every atom or atomic layer, even though such concept is not necessarily well-defined. Other approaches use the Green's function method combined with the Landauer formalism, but usually treat near-equilibrium cases using harmonic theory.In this presentation, we show a new non-equilibrium formalism which can self-consistently describe thermal expansion and heat propagation of vibrational degrees of freedom across an ordered or disordered interface at high temperatures and in anharmonic systems.