3D Radiative-hydrodynamics Research Articles

A GPU based 3D raytracing algorithm for DUED laser fusion code

Abstract These days, graphical processing units (GPUs) deliver performance
comparable to that of hundreds of CPU cores. This level of performance allows
certain classes of simulations to be run in-house on a standard consumer workstation,
eliminating the need for a cluster. In this paper, it is shown that medium-resolution,
2D radiation hydrodynamics simulations for laser-driven inertial confinement fusion
with realistic 3D laser raytracing can now be conducted on a single consumer device.
A novel raytracing module has indeed been developed for the 2D Lagrangian radiation-
hydro-nuclear code DUED to leverage the computational power of GPUs. By
employing 3D raytracing, more realistic investigations of laser-driven plasmas become
feasible, with a particular focus on perturbations resulting from non-uniform laser
irradiation.

M3DIS - A grid of 3D radiation-hydrodynamics stellar atmosphere models for stellar surveys. I. Procedure, validation, and the Sun

Large-scale stellar surveys, such as SDSS-V, 4MOST, WEAVE, and PLATO, require accurate atmospheric models and synthetic spectra of stars for accurate analyses of fundamental stellar parameters and chemical abundances. The primary goal of our work is to develop a new approach to solve radiation-hydrodynamics (RHD) and generate model stellar spectra in a self-consistent and highly efficient framework. We build upon the Copenhagen legacy RHD code, the MULTI3D non-local thermodynamic equilibrium (NLTE) code, and the DISPATCH high-performance framework. The new approach allows us to calculate 3D RHD models of stellar atmospheres on timescales of a few thousand CPU hours and to perform subsequent spectrum synthesis in local thermodynamic equilibrium (LTE) or NLTE for the desired physical conditions within the parameter space of FGK-type stars. We compare the 3D RHD solar model with other available models and validate its performance against solar observations, including the centre-to-limb variation of intensities and key solar diagnostic lines of H and Fe. We show that the performance of the new code allows to overcome the main bottleneck in 3D NLTE spectroscopy and enables calculations of multi-dimensional grids of synthetic stellar observables for comparison with modern astronomical observations.

Formation of low-mass protostars and their circumstellar disks

Understanding circumstellar disks is of prime importance in astrophysics; however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. We aim to elucidate the small-scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. We carried out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent, dense molecular cloud core to stellar densities. We studied the birth of the protostar, the circumstellar disk, and its early evolution ($<6\ yr $ after protostellar formation). Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot ($ K $), dense, and highly flared circumstellar disk. The protostar is embedded within the disk such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock was shown to be supercritical, whereas its equatorial counterpart is subcritical. We also find a remarkable convergence of our results with respect to initial conditions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger-scale physics.

The LORELI database: 21 cm signal inference with 3D radiative hydrodynamics simulations

The Square Kilometer Array is expected to measure the 21 cm signal from the Epoch of Reionization (EoR) in the coming decade, and its pathfinders may provide a statistical detection even earlier. The currently reported upper limits provide tentative constraints on the astrophysical parameters of the models of the EoR. In order to interpret such data with 3D radiative hydrodynamics simulations using Bayesian inference, we present the latest developments of the LICORICE code. Relying on an implementation of the halo conditional mass function to account for unresolved star formation, this code now allows accurate simulations of the EoR at 2563 resolution. We use this version of LICORICE to produce the first iteration of LORELI, a public dataset now containing hundreds of 21 cm signals computed from radiative hydrodynamics simulations. We train a neural network on LORELI to provide a fast emulator of the LICORICE power spectra, LOREMU, which has ∼5% rms error relative to the simulated signals. LOREMU is used in a Markov chain Monte Carlo framework to perform Bayesian inference, first on a mock observation composed of a simulated signal and thermal noise corresponding to 100 h observations with the SKA. We then apply our inference pipeline to the latest measurements from the HERA interferometer. We report constraints on the X-ray emissivity, and confirm that cold reionization scenarios are unlikely to accurately represent our Universe.

The birth and early evolution of a low-mass protostar

Context. Understanding the collapse of dense molecular cloud cores to stellar densities and the subsequent evolution of the protostar is of importance to model the feedback effects such an object has on its surrounding environment, as well as describing the conditions with which it enters the stellar evolutionary track. This process is fundamentally multi-scale, both in density and in spatial extent, and requires the inclusion of complex physical processes such as self-gravity, turbulence, radiative transfer, and magnetic fields. As such, it necessitates the use of robust numerical simulations. Aims. We aim to model the birth and early evolution of a low-mass protostar. We also seek to describe the interior structure of the protostar and the radiative behavior of its accretion shock front. Methods. We carried out a high resolution numerical simulation of the collapse of a gravitationally unstable 1 M⊙ dense molecular cloud core to stellar densities using 3D radiation hydrodynamics under the gray flux-limited diffusion approximation. We followed the initial isothermal phase, the first adiabatic contraction, the second gravitational collapse triggered by the dissociation of H2 molecules, and ≈247 days of the subsequent main accretion phase. Results. We find that the subcritical radiative behavior of the protostar’s shock front causes it to swell as it accretes matter. We also find that the protostar is turbulent from the moment of its inception despite its radiative stability. This turbulence causes significant entropy mixing inside the protostar, which regulates the swelling. Furthermore, we find that the protostar is not fully ionized at birth, but the relative amount of ionized material within it increases as it accretes matter from its surroundings. Finally, we report in the appendix the results of the first 3D calculations involving a frequency-dependent treatment of radiative transfer, which has not produced any major differences with its gray counterpart.

First indirect drive inertial confinement fusion campaign at Laser Megajoule

The first indirect drive Inertial Confinement Fusion (ICF) experiments on the Laser Megajoule facility were carried out with approximately 150 kJ of laser energy distributed on 48 beams (12 quads) arranged in two cones. The target consisted of a gold vacuum rugby-shaped hohlraum and a plastic capsule located at its center, filled with deuterium gas fuel. The arrangement of the 12 quads is such that the laser irradiation on the wall generated a three-dimensional (3D) x-ray flux around the capsule creating 3D deformations on the imploding plastic shell. This constraint forced the design of a robust target (relatively thin ablator, around 40 μm) driven by a short laser pulse (3 ns) that delivered about 1011 neutrons. Full-integrated 3D radiation hydrodynamics simulations allowed both the target definition and the data interpretation (mainly radiation temperature, x-ray images, and neutron yield). 3D calculations and experiments compare well.

Mass and Angular Momentum Transport in a Gravitationally Unstable Protoplanetary Disk with Improved 3D Radiative Hydrodynamics

During early phases of a protoplanetary disk's life, gravitational instabilities (GIs) can produce significant mass transport, can dramatically alter disk structure, can mix and shock-process gas and solids, and may be instrumental in planet formation. We present a 3D grid-based radiative hydrodynamics study with varied resolutions of a 0.07 M ⊙ disk orbiting a 0.5 M ⊙ star as it settles over most of its radial extent into a quasi-steady asymptotic state that maintains approximate balance between heating produced by GIs and radiative cooling governed by realistic dust opacities. We assess disk stability criteria, thermodynamic properties, strengths of GIs, characteristics of density waves and torques produced by GIs, radial mass transport arising from these torques, and the level to which transport can be represented as local or nonlocal processes. Physical and thermal processes display distinct differences between inner optically thick and outer optically thin regions of the disk. In the inner region, gravitational torques are dominated by low-order Fourier components of the azimuthal mass distribution. These torques are strongly variable on the local dynamical time and are subject to rapid flaring presumably driven by recurrent swing amplification. In the outer region, m = 1 torques dominate. Ring-like structures exhibiting strong noncircular motions, and vortices develop near the inner edge between 8 and 14 au. We find that GI-induced spiral modes erupt in a chaotic manner over the whole low-Q part of the disk, with many spiral modes appearing and disappearing, producing gravitoturbulence, but dominated by fluctuating large-scale modes, very different from a simple α-disk.

Formation of hot spots at end-on pre-compressed isochoric fuels for fast ignition

It is crucial to form a hot spot that can drive a self-heating nuclear burn propagation into the surrounding cold fuel in ignition process of laser fusion. In this paper, we discuss the formation of a hemispherical hot spot located at the edge of an end-on precompressed isochoric fuel instead of a central spherical hot spot surrounded by cold fuel in a corona plasma shell. This configuration leads to a new energy loss mechanism named hot spot collapse, which originates from mass loss of the hot spot through the interface with the vacuum. A semi-analytical model is proposed including α particle induced burning, hot spot collapse and other energy loss processes. Then a modified ignition criterion is derived. The results show that the competition between the hot spot collapse and the burn propagation is crucial in the formation of the hot spot. The formation of such a hot spot at end-on precompressed isochoric fuels would require a somewhat higher initial temperature of Th=9 keV for a hot spot with an initial areal density ρd=0.6gcm−2 . Simulations are performed with a 3D hybrid particle-in-cell/fluid code for the heating process by fast electrons and a 3D radiation hydrodynamics code for the burning process. Simulation results agree with the model. Our optimized result shows a 10 ps heating laser pulse with an energy as low as 39 kJ can lead to a fast ignition in the ideal case. This study provides an effective reference for design and evaluation of experiments planned for fast ignition schemes.

Multidimensional Radiation Hydrodynamics Simulations of Pulsational Pair-instability Supernovae

Stars with masses of 80–130 M ⊙ can encounter pulsational pair-instability at the end of their lives, which triggers consecutive episodes of explosive burning that eject multiple massive shells. Collisions between these shells produce bright transients known as pulsational pair-instability supernovae (PPI SNe) that may explain some extreme supernovae. In this paper, we present the first 2D and 3D radiation hydrodynamics simulations of PPI SNe with the CASTRO code. Radiative cooling causes the collided shells to evolve into thin, dense structures with hot spots that can enhance the peak luminosity of the SN by factors of 2–3. The light curve peaks at 1.9–2.1 × 1043 erg s−1 for 50 days and then plateaus at 2–3 × 1042 erg s−1 for 200 days, depending on the viewing angle. The presence of 12C and 16O and the absence of 28Si and 56Fe in its spectra can uniquely identify this transient as a PPI SN in follow-up observations. Our models suggest that multidimensional radiation hydrodynamics is required to model the evolution and light curves of all shell-collision SNe, such as Type IIne, not just PPI SNe.

Non-LTE radiative transfer with Turbospectrum

Physically realistic models of stellar spectra are needed in a variety of astronomical studies, from the analysis of fundamental stellar parameters, to studies of exoplanets and stellar populations in galaxies. Here we present a new version of the widely used radiative transfer code Turbospectrum, which we update so that it is able to perform spectrum synthesis for lines of multiple chemical elements in non-local thermodynamic equilibrium (NLTE). We use the code in the analysis of metallicites and abundances of the Gaia FGK benchmark stars, using 1D MARCS atmospheric models and the averages of 3D radiation-hydrodynamics simulations of stellar surface convection. We show that the new more physically realistic models offer a better description of the observed data, and we make the program and the associated microphysics data publicly available, including grids of NLTE departure coefficients for H, O, Na, Mg, Si, Ca, Ti, Mn, Fe, Co, Ni, Sr, and Ba.

Extensive characterization of Marshak waves observed at the LIL laser facility

We detail results of an experiment performed at the Ligne d'Intégration Laser facility aimed at studying supersonic and diffusive radiation front propagation in low-density SiO2 aerogel (20 and 40 mg/cm3) enclosed in a gold tube, driven by thermal emission from a laser-heated spherical gold cavity. The evolution of the front is studied continuously by measuring its self-emission with a 1D (one-dimensional) time-resolved soft x-ray imager. Measurement is performed along (through a 200-μm-wide observation slit) and at the exit of the tube giving access to the dynamics and the curvature of the front. Experimental results are then compared successfully to results from the 3D (three-dimensional) radiation hydrodynamics code TROLL, which shows that if continuous tracking of the front position is accessible with this experimental scheme, measurement of its maximum radiation temperature is on the contrary affected by radiation closure of the observation slit. 3D simulations also indicate that this effect can even be worsened if one includes pointing errors of the x-ray imager. Radiation temperature along the tube was then inferred by combining results from the imager to a wall shock breakout time measurement using a velocity interferometer system for any reflector and results from a broadband x-ray spectrometer used to determine the temperature at the exit of the tube. A decrease in the radiation temperature along the tube is observed, the decrease being more important for the higher SiO2 aerogel density.

Leptocline as a shallow substructure of near-surface shear layer in 3D radiative hydrodynamic simulations

ABSTRACT Understanding the effects driven by rotation in the solar convection zone is essential for many problems related to solar activity, such as the formation of differential rotation, meridional circulation, and others. We analyse realistic 3D radiative hydrodynamics simulations of solar subsurface dynamics in the presence of rotation in a local domain 80 Mm wide and 25 Mm deep, located at 30° latitude. The simulation results reveal the development of a shallow 10 Mm deep substructure of the near-surface shear layer (NSSL), characterized by a strong radial rotational gradient and self-organized meridional flows. This shallow layer (‘leptocline’) is located in the hydrogen ionization zone associated with enhanced anisotropic overshooting-type flows into a less unstable layer between the H and He ii ionization zones. We discuss current observational evidence of the presence of the leptocline and show that the radial variations of the differential rotation and meridional flow profiles obtained from the simulations in this layer qualitatively agree with helioseismic observations.

The burst mode of accretion in massive star formation with stellar inertia

ABSTRACT The burst mode of accretion in massive star formation is a scenario linking the initial gravitational collapse of parent pre-stellar cores to the properties of their gravitationally unstable discs and of their accretion-driven bursts. In this study, we present a series of high-resolution 3D radiation-hydrodynamics numerical simulations for young massive stars formed out of collapsing $100{\rm M}_{\odot }$ molecular cores, spinning with several values of the ratio of rotational-to-gravitational energies $\beta =5{{-}9\ per cent}$. The models include the indirect gravitational potential caused by disc asymmetries. We find that this modifies the barycentre of the disc, causing significant excursions of the central star position, which we term stellar wobbling. The stellar wobbling slows down and protracts the development of gravitational instability in the disc, reducing the number and magnitude of the accretion-driven bursts undergone by the young massive stars, whose properties are in good agreement with that of the burst monitored from the massive protostar M17 MIR. Including stellar wobbling is therefore important for accurate modelling disc structures. Synthetic alma interferometric images in the millimetre waveband show that the outcomes of efficient gravitational instability such as spiral arms and gaseous clumps can be detected for as long as the disc is old enough and has already entered the burst mode of accretion.

Investigating laser ablated plume dynamics of carbon and aluminum targets

Recently acquired high-resolution images of nanosecond laser ablation plumes suggest a strong correlation between the internal plume structure and the type of material being ablated. However, the details of this relation are currently not well understood. In this work, we attempt to explore this correlation using a 2D radiation hydrodynamics model to study the dependence of internal plume structure formation on the ablation material. Spatio-temporal emission maps and plume expansion velocities from experimental measurements are compared with the model predictions, including synthetic emission maps. The shape and expansion rate of an outer air plume region are found to be in good agreement for both carbon and aluminum, as are the inner material plume dynamics for carbon ablation. The largest disagreement is observed in the case of a polished aluminum target, where the chaotic inner plume features seen in the experimental images are not observed in the model. The possible physical mechanisms responsible for this discrepancy are discussed. This effort constitutes a continued development toward a predictive model of ablation plume dynamics and chemistry for various materials in extreme environments.

Observational constraints on the origin of the elements

Context.The chemical composition of the Sun is required in the context of various studies in astrophysics, among them in the calculation of standard solar models (SSMs) used to describe the evolution of the Sun from the pre-main-sequence to its present age.Aims.In this work, we provide a critical re-analysis of the solar chemical abundances and corresponding SSMs.Methods.For the photospheric values, we employed new high-quality solar observational data collected with the IAG facility, state-of-the art non-equilibrium modelling, new oscillator strengths, and different atmospheric models, including the MARCS model, along with averages based on Stagger and CO5BOLD 3D radiation-hydrodynamics simulations of stellar convection. We performed new calculations of oscillator strengths for transitions in O I and N I. For O I, which is a critical element with regard to the interior models, calculations were carried out using several independent methods. We investigated our results in comparison with the previous estimates.Results.We find an unprecedented agreement between the new estimates of transition probabilities, thus supporting our revised solar oxygen abundance value. We also provide new estimates of the noble gas Ne abundance. In addition, we discuss the consistency of our photospheric measurements with meteoritic values, taking into account the systematic and correlated errors. Finally, we provide revised chemical abundances, leading to a new value proposed for the solar photospheric present-day metallicity of Z/X = 0.0225, which we then employed in SSM calculations. We find that the puzzling mismatch between the helioseismic constraints on the solar interior structure and the model can be resolved thanks to this new chemical composition.

The extended atmosphere and circumstellar environment of the cool evolved star VX Sagittarii as seen by MATISSE

Context. VX Sgr is a cool, evolved, and luminous red star whose stellar parameters are difficult to determine, which affects its classification. Aims. We aim to spatially resolve the photospheric extent as well as the circumstellar environment. Methods. We used interferometric observations obtained with the MATISSE instrument in the L (3–4 μm), M (4.5–5 μm), and N (8–13 μm) bands. We reconstructed monochromatic images using the MIRA software. We used 3D radiation-hydrodynamics simulations carried out with CO5BOLD and a uniform disc model to estimate the apparent diameter and interpret the stellar surface structures. Moreover, we employed the radiative transfer codes OPTIM3D and RADMC3D to compute the spectral energy distribution for the L, M, and N bands, respectively. Results. MATISSE observations unveil, for the first time, the morphology of VX Sgr across the L, M, and N bands. The reconstructed images show a complex morphology with brighter areas whose characteristics depend on the wavelength probed. We measured the angular diameter as a function of the wavelength and showed that the photospheric extent in the L and M bands depends on the opacity through the atmosphere. In addition to this, we also concluded that the observed photospheric inhomogeneities can be interpreted as convection-related surface structures. The comparison in the N band yielded a qualitative agreement between the N-band spectrum and simple dust radiative transfer simulations. However, it is not possible to firmly conclude on the interpretation of the current data because of the difficulty in constraing the model parameters using the limited accuracy of our absolute flux calibration. Conclusions. MATISSE observations and the derived reconstructed images unveil the appearance of VX Sgr’s stellar surface and circumstellar environment across a very large spectral domain for the first time.

Improvement of ignition and burning target design for fast ignition scheme

For the fast ignition scheme of laser fusion, a highly compressed fuel core is necessary using a cone-inserted spherical solid target. We design an optimal compression method with a multistep laser pulse shape using a 2D radiation hydrodynamics simulation. In the design, the maximum areal density is ρR max = 0.46 g cm−2 with 8 kJ of implosion laser. Considering the scaling law of hydrodynamic, we obtained 82 kJ and 1.3 MJ for the ignition-scale-target (ρR max = 1.1 g cm−2) and burning-scale-target (ρR max = 2.5 g cm−2), respectively. In a preliminary study of hydrodynamic instability in the optimized cone-inserted implosion, there is no significant growth of the instabilities that affect the implosion performance. A parameter search to investigate the feasibility and robustness of a high areal density design for changes in the laser pulse shape is performed. As a result, a delay of several tens of pico-second of the rising laser pulse is acceptable.

Radiation hydrodynamics simulations of line-driven AGN disc winds: metallicity dependence and black hole growth

ABSTRACT Growth of the black holes (BHs) from the seeds to supermassive BHs (SMBHs, $\sim \!10^9\, M_\odot$) is not understood, but the mass accretion must have played an important role. We performed 2D radiation hydrodynamics simulations of line-driven disc winds considering the metallicity dependence in a wide range of the BH mass, and investigated the reduction of the mass accretion rate due to the wind mass-loss. Our results show that denser and faster disc winds appear at higher metallicities and larger BH masses. The accretion rate is suppressed to ∼0.4–0.6 times the mass supply rate to the disc for the BH mass of $M_{\rm BH}\gtrsim 10^5\, M_{\odot }$ in high-metallicity environments of Z ≳ Z⊙, while the wind mass-loss is negligible when the metallicity is subsolar (∼0.1Z⊙). By developing a semi-analytical model, we found that the metallicity dependence of the line force and the BH mass dependence of the surface area of the wind launch region are the cause of the metallicity dependence (∝ Z2/3) and BH mass dependencies ($\propto \! M_{\rm BH}^{4/3}$ for $M_{\rm BH}\le 10^6\, M_\odot$ and ∝ MBH for $M_{\rm BH}\ge 10^6\, M_\odot$) of the mass-loss rate. Our model suggests that the growth of BHs by the gas accretion effectively slows down in the regime ≳ 105M⊙ in metal-enriched environments ≳ Z⊙. This means that the line-driven disc winds may have an impact on late evolution of SMBHs.

Radiation hydrodynamics simulations of massive star cluster formation in giant molecular clouds

ABSTRACT By performing 3D radiation hydrodynamics simulations, we study the formation of young massive star clusters (YMCs; M* > 104 M⊙) in clouds with the surface density ranging from Σcl = 80 to 3200 M⊙ pc−2. We find that photoionization feedback suppresses star formation significantly in clouds with low-surface density. Once the initial surface density exceeds ∼100 M⊙ pc−2 for clouds with Mcl = 106 M⊙ and Z = Z⊙, most of the gas is converted into stars because the photoionization feedback is inefficient in deep gravitational potential. In this case, the star clusters are massive and gravitationally bounded as YMCs. The transition surface density increases as metallicity decreases, and it is ∼350 M⊙ pc−2 for Z = 10−2 Z⊙. We show that more than 10 per cent of star formation efficiency (SFE) is needed to keep a star cluster gravitationally bounded even after the disruption of a cloud. Also, we develop a semi-analytical model reproducing the SFEs obtained in our simulations. We find that the SFEs are fit with a power-law function with the dependence ${\propto}\Sigma _{\rm cl}^{1/2}$ for low-surface density and rapidly increases at the transition surface densities. The conditions of the surface density and the metallicity match recent observations of giant molecular clouds forming YMCs in nearby galaxies.

Femtosecond, two-dimensional spatial Doppler mapping of ultraintense laser-solid target interaction

We present measurements of the spatiotemporal evolution of a hot-dense plasma generated by the interaction of an intense 25 fs laser pulse with a solid target, using pump-probe two-dimensional (2D) Doppler spectrometry. Measuring the time-dependent Doppler shifts at different positions across the probe beam, we achieve velocity mapping at hundreds of femtoseconds time resolution simultaneously with a few micrometer spatial resolution across the transverse length of the plasma. Simulations of the interaction using a combination of 2D particle-in-cell and 2D radiation hydrodynamics codes agree well with the experiment.