Enhancing the conversion efficiency of extreme ultraviolet light sources using a 2 µm-wavelength laser

In this study, we use the FLASH radiation hydrodynamic code and the FLYCHK atomic code to investigate the energy conversion and spectra associated with laser–Sn target interactions with 1 µm and 2 µm wavelength lasers. We found that the conversion efficiency (CE) reached as much as 3.38% with the 2 µm laser, which is 1.48 percentage points higher than the 1 µm laser (CE = 1.9%). In addition, we analyzed the contribution of dominant ionization states to the emission spectrum for both lasers. We observed that the growths of the out-of-band emission eventually led to a broadening of the spectrum, resulting in a reduction of SP for the 1 µm laser. By contrast, the emission main peaks were all centered near 13.5nm for the 2 µm laser, which is beneficial for efficient emission of light with a 13.5 nm wavelength (relevant for nanolithographic applications).

Modification of the radiation transfer equations to take into account NLTE effects in the simulations of supernova light curves by the radiation hydrodynamic code STELLA

The observed supernova broadband light curves serve as an extensive source of information about the physics of presupernovae and about the processes taking place during supernova outbursts. Their modeling requires complex calculations using radiation-hydrodynamic codes. The paper proposes to modify the STELLA radiation-hydrodynamic code to take into account NLTE (local thermodynamic equilibrium) effects in the calculation of supernova light curves. The paper provides a theoretical justification for the need to take into account the effects of NLTE when calculating the level number densities of multicharged plasma in a supernova envelope. A modification of equations of time-dependent radiation transfer and the equation of gas energy to take into account the NLTE effects is described. Various methods of mean opacity coefficients in the expanding envelope of supernovae are analyzed.

The evolution of a circumplanetary disc with a dead zone

ABSTRACT We investigate whether the regular Galilean satellites could have formed in the dead zone of a circumplanetary disc. A dead zone is a region of weak turbulence in which the magnetorotational instability is suppressed, potentially an ideal environment for satellite formation. With the grid-based hydrodynamic code fargo3d, we examine the evolution of a circumplanetary disc model with a dead zone. Material accumulates in the dead zone of the disc leading to a higher total mass and but a similar temperature profile compared to a fully turbulent disc model. The tidal torque increases the rate of mass transport through the dead zone leading to a steady-state disc with a dead zone that does not undergo accretion outbursts. We explore a range of disc, dead zone, and mass inflow parameters and find that the maximum mass of the disc is around $0.001 M_{\rm J}$. Since the total solid mass of such a disc is much lower, we find that there is not sufficient material in the disc for in situ formation of the Galilean satellites and that external supplement is required.

How fast do young star clusters expel their natal gas? Estimating the upper limit of the gas expulsion time-scale

ABSTRACT Formation of massive stars within embedded star clusters starts a complex interplay between their feedback, inflowing gas, and stellar dynamics, which often includes close stellar encounters. Hydrodynamical simulations usually resort to substantial simplifications to model embedded clusters. Here, we address the simplification which approximates the whole star cluster by a single sink particle, which completely neglects the internal stellar dynamics. In order to model the internal stellar dynamics, we implement a Hermite predictor–corrector integration scheme to the hydrodynamic code flash. As we illustrate by a suite of tests, this integrator significantly outperforms the current leap-frog scheme, and it is able to follow the dynamics of small compact stellar systems without the necessity to soften the gravitational potential. We find that resolving individual massive stars instead of representing the whole cluster by a single energetic source has a profound influence on the gas component: for clusters of mass less than $\approx3 \times 10^3 \, \mathrm{M}_{\odot }$ , it slows gas expulsion by a factor of ≈5 to $\approx 1 \, \mathrm{Myr}$, and it results in substantially more complex gas structures. With increasing cluster mass (up to $\approx 3\times 10^3 \, \mathrm{M}_{\odot }$), the gas expulsion time-scale slightly decreases. However, more massive clusters ($\gtrsim 5\times 10^3 \, \mathrm{M}_{\odot }$) are unable to clear their natal gas with photoionizing radiation and stellar winds only if they form with a star formation efficiency (SFE) of 1/3. This implies that the more massive clusters are either cleared with another feedback mechanism or they form with an SFE higher than 1/3.

Powering galactic superwinds with small-scale AGN winds

ABSTRACT We present a new implementation for active galactic nucleus (AGN) feedback through small-scale, ultrafast winds in the moving-mesh hydrodynamic code arepo. The wind is injected by prescribing mass, momentum, and energy fluxes across a spherical boundary centred on a supermassive black hole according to available constraints for accretion disc winds. After sweeping-up a mass equal to their own, small-scale winds thermalize, powering energy-driven outflows with dynamics, structure, and cooling properties in excellent agreement with those of analytic wind solutions. Momentum-driven solutions do not easily occur, because the Compton cooling radius is usually much smaller than the free-expansion radius of the small-scale winds. Through various convergence tests, we demonstrate that our implementation yields wind solutions, which are well converged down to the typical resolution achieved in cosmological simulations. We test our model in hydrodynamic simulations of isolated Milky Way – mass galaxies. Above a critical AGN luminosity, initially spherical, small-scale winds power bipolar, energy-driven superwinds that break out of the galactic nucleus, flowing at speeds $\gt 1000 \rm \, km \, s^{-1}$ out to $\sim 10 \, \rm kpc$. These energy-driven outflows result in moderate, but long-term, reduction in star formation, which becomes more pronounced for higher AGN luminosities and faster small-scale winds. Suppression of star formation proceeds through a rapid mode that involves the removal of the highest density, nuclear gas, and through a slower mode that effectively halts halo gas accretion. Our new implementation makes it possible to model AGN-driven winds in a physically meaningful and validated way in simulations of galaxy evolution, the interstellar medium and black hole accretion flows.

The final fate of supermassive M ∼ 5 × 104 M⊙ Pop III stars: explosion or collapse?

ABSTRACT We investigate the possibility of a supernova in supermassive (5 × 104 M⊙) population III stars induced by a general relativistic instability occurring in the helium burning phase. This explosion could occur via rapid helium burning during an early contraction of the isentropic core. Such an explosion would be visible to future telescopes and could disrupt the proposed direct collapse formation channel for early Universe supermassive black holes. We simulate first the stellar evolution from hydrogen burning using a 1D stellar evolution code with a post-Newtonian approximation; at the point of dynamical collapse, we switch to a 1D (general relativistic) hydrodynamic code with the Misner-Sharpe metric. In opposition to a previous study, we do not find an explosion in the non-rotating case, although our model is close to exploding for a similar mass to the explosion in the previous study. When we include slow rotation, we find one exploding model, and we conclude that there likely exist additional exploding models, though they may be rare.

CFD Modelling of Particle-Driven Gravity Currents in Reservoirs

Reservoir sedimentation results in ongoing loss of storage capacity all around the world. Thus, effective sediment management in reservoirs is becoming an increasingly important task requiring detailed process understanding. Computational fluid dynamics modelling can provide an efficient means to study relevant processes. An existing in-house hydrodynamic code has been extended to model particle-driven gravity currents. This has been realised through a buoyancy term which was added as a source term to the momentum equation. The model was successfully verified and validated using literature data of lock exchange experiments. In addition, the capability of the model to optimize venting of turbidity currents as an efficient sediment management strategy for reservoirs was tested. The results show that the concentration field during venting agrees well with observations from laboratory experiments documented in literature. The relevance of particle-driven gravity currents for the flow field in reservoirs is shown by comparing results of simulations with and without buoyant forces included into the model. The accuracy of the model in the area of the bottom outlet can possibly be improved through the implementation of a non-upwind scheme for the advection of velocity.

Common Envelope Evolution on a Moving Mesh

The common envelope phase in binary star systems is simulated using the 3-D moving-mesh hydrodynamic code MANGA. Improvements to MANGA to improve accuracy and computation time are discussed. Two open questions in the physics of common envelope evolution are investigated. The effects of tidal forces present before the onset of a common envelope phase are explored by comparing simulations in which the giant star is initialized with varying degrees of rotation. The role of hydrogen recombination energy is investigated by using two different equations of state, only one of which includes the effects of recombination. Rotation is shown to increase the final binary separation, while recombination energy decreases the separation. Future improvements to MANGA to capture additional physics present in common envelopes are discussed.