Thermomechanical response of thickly tamped targets and diamond anvil cells under pulsed hard x-ray irradiation

Abstract

In the laboratory study of extreme conditions of temperature and density, the exposure of matter to high intensity radiation sources has been of central importance. Here we interrogate the performance of multi-layered targets in experiments involving high intensity, hard x-ray irradiation, motivated by the advent of extremely high brightness hard x-ray sources, such as free electron lasers and 4 th-generation synchrotron facilities. Intense hard x-ray beams can deliver significant energy in targets having thick x-ray transparent layers (tampers) around samples of interest, for the study of novel states of matter and materials' dynamics. Heated-state lifetimes in such targets can approach the microsecond level, regardless of radiation pulse duration, enabling the exploration of conditions of local thermal and thermodynamic equilibrium at extreme temperature in solid density matter. The thermal and mechanical response of such thick layered targets following x-ray heating, including hydrodynamic relaxation and heat flow on picosecond to millisecond timescales, is modeled using radiation hydrocode simulation, finite element analysis, and thermodynamic calculations. Assessing the potential for target survival over one or more exposures, and resistance to damage arising from heating and resulting mechanical stresses, this study doubles as an investigation into the performance of diamond-anvil high pressure cells under high x-ray fluences. Long used in conjunction with synchrotron x-ray radiation and high power optical lasers, the strong confinement afforded by such cells suggests novel applications at emerging high intensity x-ray facilities and new routes to studying thermodynamic equilibrium states of warm, very dense matter.

Intense Reactivity in Sulfur–Hydrogen Mixtures at High Pressure under X-ray Irradiation

“…This was interpreted as a rapidly-produced bubble of the reaction product H 2 S, the stable hydride of S at these pressures. The motion is consistent with a dense H 2 S vesicle (1.03 g cm −3 ) 29 sinking through the lower density molecular hydrogen medium (0.10 g cm −3 ), 30 where isothermal equations of state are used as heat associated with the reaction should dissipate within milliseconds, 31 before the bubble moves. Following Stokes law for a spherical particle falling through a fluid, 32 the velocity v is related to the medium viscosity µ, particle radius R, and densities of the particle (ρ p ) and medium (ρ m ), as…”

“…This hot state in the S 8 persists on timescales of ∼ 10 −6 seconds before quenching and will additionally heat the surrounding hydrogen to high temperatures. 31 Temperature induced reaction and subsequent formation of hydrides under pressure is well documented, for example as a result of laser-heating S in H 2 , 9,10,19 and gentle heating of Se in H 2 at 473 K. 12 The equilibrium peak temperature (before heat dissipation) in these experiments can be estimated as 31 T − T 0 = H…”

“…20 While these qualitative comparisons suggest that the total dose and the photon energy are critical parameters, nonlinear effects of high beam intensity including multiple ionization, bulk chemical disruption, and sample heating may also be enhancing the reaction intensity. Concomitant with electronic chemical disruption is the rapid thermalization of the hot electrons on a timescale of ∼ 10 −12 seconds, 28,31 leading to an equilibrium heated state in S 8 (direct heating of H 2 is negligible). This hot state in the S 8 persists on timescales of ∼ 10 −6 seconds before quenching and will additionally heat the surrounding hydrogen to high temperatures.…”

Novel experimental setup for megahertz X-ray diffraction in a diamond anvil cell at the High Energy Density (HED) instrument of the European X-ray Free-Electron Laser (EuXFEL)

“…metallic) surfaces of the sample, bulk sample heating can be achieved without the need for heat to conduct through the sample, which could also have benefits in controlling and minimizing temperature gradients. X-ray heating in a DAC has been evaluated through finite element simulations in recent work by Meza-Galvez et al (2020). This work proposes to utilize the different timescales of XRD and X-ray absorption, whereby XRD is immediate and occurs before any subsequent unit-cell expansion due to X-ray absorption.…”

“…Current explorations of how best to integrate DAC techniques with XFEL sources focus on probing conditions of rapidly varying pressure and temperature states using piezoelectrically driven pressure cells (dynamic DAC or dDAC) and pulsed optical laser heating (e.g. Liermann, 2014;Liermann et al, 2016), or the use of the X-ray source itself for dynamic excitation (Meza-Galvez et al, 2020;Pace et al, 2020).…”