The results of a commissioning experiment on the SILEX-Ⅱ laser facility (formerly known as CAEP-PW) are reported. SILEX-Ⅱ is a complete optical parametric chirped-pulse amplification laser facility. The peak power reached about 1 PW in a 30 fs pulse duration during the experiment. The laser contrast was better than 1010 at 20 ps ahead of the main pulse. In the basic laser foil target interaction, a set of experimental data were collected, including spatially resolved x-ray emission, the image of the coherent transition radiation, the harmonic spectra in the direction of reflection, the energy spectra and beam profile of accelerated protons, hot-electron spectra, and transmitted laser energy fraction and spatial distribution. The experimental results show that the laser intensity reached 5 × 1020 W/cm2 within a 5.8 µm focus (FWHM). Significant laser transmission did not occur when the thickness of the CH foil was equal to or greater than 50 nm. The maximum energy of the accelerated protons in the target normal direction was roughly unchanged when the target thickness varied between 50 nm and 15 µm. The maximum proton energy via the target normal sheath field acceleration mechanism was about 21 MeV. We expect the on-target laser intensity to reach 1022 W/cm2 in the near future, after optimization of the laser focus and upgrade of the laser power to 3 PW.

We present the results of the first commissioning phase of the short-focal-length area of the Apollon laser facility (located in Saclay, France), which was performed with the first available laser beam (F2), scaled to a nominal power of 1 PW. Under the conditions that were tested, this beam delivered on-target pulses of 10 J average energy and 24 fs duration. Several diagnostics were fielded to assess the performance of the facility. The on-target focal spot and its spatial stability, the temporal intensity profile prior to the main pulse, and the resulting density gradient formed at the irradiated side of solid targets have been thoroughly characterized, with the goal of helping users design future experiments. Emissions of energetic electrons, ions, and electromagnetic radiation were recorded, showing good laser-to-target coupling efficiency and an overall performance comparable to that of similar international facilities. This will be followed in 2022 by a further commissioning stage at the multi-petawatt level.

Although it was proposed many years ago that compressed hydrogen should be a high-temperature superconductor, the goal of room-temperature superconductivity has so far remained out of reach. However, the successful synthesis of the theoretically predicted hydrides H3S and LaH10 with high superconducting transition temperatures TC provides clear guidance for achieving this goal. The existence of these superconducting hydrides also confirms the utility of theoretical predictions in finding high-TC superconductors. To date, numerous hydrides have been studied theoretically or experimentally, especially binary hydrides. Interestingly, some of them exhibit superconductivity above 200 K. To gain insight into these high-TC hydrides (>200 K) and facilitate further research, we summarize their crystal structures, bonding features, and electronic properties, as well as their superconducting mechanism. Based on hydrogen structural motifs, covalent H3S with isolated hydrogen and several clathrate superhydrides (LaH10, YH9, and CaH6) are highlighted. Other predicted hydrides with various H-cages and two-dimensional H motifs are also discussed. Finally, we present a systematic discussion of the common features, current problems, and future challenges of these high-TC hydrides.

Synchrotron sources with high photon flux, small source size, and broad energy range have revolutionized ultrafine characterization of condensed matter. With the addition of the pressure dimension realized by the use of diamond anvil cells, enormous progress has been achieved throughout high-pressure science. This is particularly so for synchrotron-based infrared microspectroscopy (SIRMS) with its very high signal-to-noise ratio, high spatial resolution, and extended measurement conditions. SIRMS has high sensitivity, providing a platform for the investigations of the very small amounts of material that need to be used in high-pressure research. This review summarizes developments in SIRMS, focusing on instrumentation and high-pressure measurements. Applications to measurements of infrared reflectance and absorption are presented, illustrating how SIRMS results play a crucial role in advancing understanding of the crystalline phase transitions, electronic transitions, metallization, lattice dynamics, superconductivity, and novel functional behavior. New insights into spectroscopic properties, together with some cutting edge issues and open problems, are also briefly discussed.

We report significant differences in high-pressure properties of vanadium at zero temperature and finite temperature when different projector augmented wave (PAW) potentials are used in simulations based on density functional theory. When a PAW potential with only five electrons taken as valence electrons is used, the cold pressures in the high-pressure region are seriously underestimated, and an abnormality occurs in the melting curve of vanadium at about 400 GPa. We show that the reason for these discrepancies lies in the differences in the descriptions of the interatomic force, electron dispersion, and anisotropy of electron bonding obtained from different PAW potentials at high pressure, which lead to striking differences in the mechanical stability of the system. We propose a procedure for selecting PAW potentials suitable for simulations at high temperature and high pressure. Our results provide valuable guidance for future simulations of thermodynamic properties under extreme conditions.

Recent developments in in situ nuclear magnetic resonance (NMR) spectroscopy under extreme conditions have led to the observation of a wide variety of physical phenomena that are not accessible with standard high-pressure experimental probes. However, inherent di- or quadrupolar line broadening in diamond anvil cell (DAC)-based NMR experiments often limits detailed investigation of local atomic structures, especially if different phases or local environments coexist. Here, we describe our progress in the development of high-resolution NMR experiments in DACs using one- and two-dimensional homonuclear decoupling experiments at pressures up to the megabar regime. Using this technique, spectral resolutions of the order of 1 ppm and below have been achieved, enabling high-pressure structural analysis. Several examples are presented that demonstrate the wide applicability of this method for extreme conditions research.

Born’s valence force-field model (VFM) established a theoretical scheme for calculating the elasticity, zero-point optical mode, and lattice dynamics of diamond and diamond-structured solids. In particular, the model enabled the derivation of a numerical relation between the elastic moduli and the Raman-active F2g mode for diamond. Here, we establish a relation between the diamond Raman frequency ω and the bulk modulus K through first-principles calculation, rather than extrapolation. The calculated K exhibits a combined uncertainty of less than 5.4% compared with the results obtained from the analytical equation of the VFM. The results not only validate Born’s classic model but also provide a robust K–ω functional relation extending to megabar pressures, which we use to construct a primary pressure scale through Raman spectroscopy and the crystal structure of diamond. Our computations also suggest that currently used pressure gauges may seriously overestimate pressures in the multi-megabar regime. A revised primary scale is urgently needed for such ultrahigh pressure experiments, with possible implications for hot superconductors, ultra-dense hydrogen, and the structure of the Earth’s core.

Magnetic diffusion plays an important role in inertial confinement fusion with strong magnetic fields. In this paper, we improve a previous analysis of the generation and diffusion of the magnetic field [Morita et al., Phys. Plasmas 25, 094505 (2018)]. For the generation process, we calculate the temporal evolution of the coil current using a self-consistent circuit model. The results show that the peak of the calculated magnetic field is delayed by 1.2 ns compared with that of the incident laser pulse. For the diffusion process, we evaluate the electrical conductivity of warm dense gold over a wide temperature range (300 K–100 eV) by combining the Kubo–Greenwood formula based on a quantum molecular dynamics simulation with the modified Spitzer model. Our simulation shows that the maximum magnetic field (530 T) that penetrates the cone is delayed by 2.5 ns compared with the laser peak. This result is consistent with experiments [Sakata et al., Nat. Commun. 9, 3937 (2018)] that showed that applying a strong magnetic field improved the heating efficiency of fusion fuel.

Magnetic fields are well known to affect the evolution of fluids via the J × B force, where J is the current density and B is the magnetic field. This force leads to the influence of magnetic fields on hydrodynamics (magnetohydrodynamics). Magnetic fields are often neglected in modeling of high-energy-density plasmas, since J × B is very small compared with the plasma pressure gradients. However, many experiments lie in a separate part of parameter space where the plasma is indirectly affected via magnetization of the heat flux and charged particle transport. This is true even for initially unmagnetized plasmas, since misaligned density and temperature gradients can self-generate magnetic fields. By comparing terms in the induction equation, we go on to estimate the regions of parameter space where these self-generated fields are strong enough to affect the hydrodynamics.

In inertial confinement fusion (ICF), overlapping of laser beams is common. Owing to the effective high laser intensity of the overlapped beams, the collective mode of stimulated Brillouin scattering (SBS) with a shared scattered light wave is potentially important. In this work, an exact analytic solution for the convective gain coefficient of the collective SBS modes with shared scattered wave is presented for two overlapped beams based on a linear kinetic model. The effects of the crossing angle, polarization states, and finite beam overlapping volume of the two laser beams on the shared light modes are analyzed for cases with zero and nonzero wavelength difference between the two beams. It is found that all these factors have a significant influence on the shared light modes of SBS. Furthermore, the out-of-plane modes, in which the wavevectors of daughter waves lie in different planes from the two overlapped beams, are found to be important for certain polarization states and especially for obtuse crossing angles. In particular, adjusting the polarization directions of the two beams to be orthogonal to each other or tuning the wavelength difference to a sufficiently large value (of the order of nanometers) are found to be effective methods to suppress the shared light modes of SBS. This work will be helpful for comprehending and suppressing collective SBS with shared scattered waves in ICF experiments.

Hydrogen (H) is the most abundant element in the known universe, and on the Earth’s surface it bonds with oxygen to form water, which is a distinguishing feature of this planet. In the Earth’s deep mantle, H is stored hydroxyl (OH-) in hydrous or nominally anhydrous minerals. Despite its ubiquity on the surface, the abundance of H in the Earth’s deep interior is uncertain. Estimates of the total H budget in the Earth’s interior have ranged from less than one hydrosphere, which assumes an H-depleted interior, to hundreds of hydrospheres, which assumes that H is siderophile (iron-loving) in the core. This discrepancy raises the questions of how H is stored and transported in the Earth’s deep interior, the answers to which will constrain its behavior in the deep lower mantle, which is defined as the layer between 1700 km depth and the core–mantle boundary.