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 pressure, temperature, and timescale, the irradiation of matter by high intensity sources has been of central importance.Here we investigate the performance of layered targets in experiments involving very high intensity hard x-ray irradiation, motivated by the advent of extremely high brightness x-ray sources such as free electron lasers. These sources enable massive (µm to mm) scale targets with confinement of the directly irradiated regions by thick, x-ray transparent tampers. The thermal and mechanical response of these layers, from femtosecond-picosecond energy delivery, to mechanical relaxation on nanosecond timescales and heat flow and dissipation on microseconds, is controlled by the differential energy deposition, shock and release wave production, and thermal transport properties. Sample survival over one or more exposures can depend on damage arising from heating or mechanical stresses induced by heating, depending on the materials used and target geometry. This study also doubles as an investigation into the properties of diamond anvil high pressure cells, long used in conjunction with x-ray synchrotron sources, at new high intensity x-ray beamlines at free electron lasers and upgraded synchrotrons. Configuring a tamped target as a high pressure cell confers certain advantages, such as resistance to expansion and thermal stresses, and sample confinement, in conjunction with efficient control of heat. This study suggests new routes to studying thermodynamic equilibrium states of high energy density matter via the capacity to confine extreme states for particularly long durations.

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 Laboratory (PAL-XFEL).…”

“…This hot state in the S 8 persists on time scales 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…”

“…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 time scale 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 time scales of ∼10 −6 seconds before quenching and will additionally heat the surrounding hydrogen to high temperatures.…”