High Energy Density Physics最新文献

In the present work, we compute the amplitude of the real part of the electronic collision operator for the electron broadening of hydrogenic ion lines in plasmas, taking into account the screening effects (the interaction between the free electron (perturber) and the ion (emitter) is governed by Debye potential) and relativistic effects in the dynamics of the perturbing electron. The screening effects are included using the cross section calculated by Debye potential instead of Rutherford cross section and the relativistic effects are included by the modification of the velocity distribution (Maxwell–Jûttner) instead of (Maxwell–Boltzmann) distribution and relativistic mass (mass depend on the velocity). The obtained results are compared with Griem’s theoretical work.

We focus on the collision dissociation process of O₂+O₂→O+O+O₂ at high temperatures (8000 K–30000 K). The research method is the new general non-equilibrium dynamics model proposed by Singh et al. The model parameters are determined by calculating the dissociation probability under the specific vibrational energy and the energy distribution functions in the quasi-steady state (QSS). It is found that the dissociation rate is more easily at high vibrational energy levels. Moreover, the energy distribution function deviates from the Boltzmann distribution in the QSS state. We obtain the dissociation rate coefficients at high temperatures by integrating the dissociation probability and the internal energy distribution functions (the Boltzmann distribution, the QSS state distribution, and the non-Boltzmann distribution). Our results demonstrate that the rate coefficients depend on the vibrational temperature and more strongly at a lower translational temperature.

Spectral diagnostics provide a powerful probe of high energy-density physics experiments. By shining an x-ray source on a target, absorption features can be used to determine accurate temperature profiles of that target material. Many studies produce a single temperature/density measurement by fitting these observed spectra. This paper demonstrates how, by leveraging detailed simulations, we can not only measure the average temperature and density, but the full density and temperature profiles. To do so, we must conduct a careful analysis of the uncertainties in the diagnostic measurement. We discuss the characteristics and associated uncertainties of the spectral diagnostic used in the COAX, Radishock and OuTi experiments, ultimately demonstrating how these detailed studies increase the potential of this powerful probe.

For diagnosing temperatures of high-energy-density plasmas, relying on the ratio of a pair of isoelectronic spectral lines provides the alternative of “matched charge-state transits in different elements” to the more conventional, “unmatched charge-state transits in the same-element” spectral-line-ratio technique. In contrast to a novel previous establishment of isoelectronic emission-line ratio determination of plasma temperature, this report determines plasma temperature from the ratio of isoelectronic absorption spectral line pairs. The feasibility of this technique is assessed from experimentally acquired transmission spectra, spanning the 7–15 Å  range, through a $0.4\mu m$ MgO-NaF foil, tamped with CH, x-ray-radiation heated by a z-pinch dynamic hohlraum (ZPDH), and backlit by the brief X-ray burst upon imploding-wire stagnation on the Z pulsed-power facility at Sandia National Laboratories. As expected from the slight difference between interstage and isoelectronic absorption processes, a quantitative comparison between the value of isoelectronic-absorption-derived temperature and the value of inter-stage-absorption-derived temperature is shown to yield a well correlated, slight difference in inferred values of plasma temperature associated with local thermodynamic equilibrium.

We present extensive new Ab initio path integral Monte Carlo (PIMC) simulations of the uniform electron gas (UEG) in the high-temperature regime, $8\le \theta =k_{B}T/E_F\le 128$. This allows us to study the convergence of different properties towards the classical limit. In particular, we investigate the classical relation between the static structure factor $S\left(q\right)$ and the static local field correction $G\left(q\right)$, which is only fulfilled at low densities. Moreover, we compare our new results for the interaction energy to the parametrization of the UEG by Groth et al. (2017), which interpolates between PIMC results for $\theta \le 8$ and the Debye–Hückel limit, and to higher order analytical virial expansions. Finally, we consider the momentum distribution function $n\left(q\right)$ and find an interaction-induced increase in the occupation of the zero-momentum state even for $\theta \gtrsim 32$. All PIMC data are freely available online, and can be used as input for improved parametrizations and as a rigorous benchmark for approximate methods.

Inertial Confinement Fusion involves the implosion of a spherical capsule containing thermonuclear fuel. The implosion is driven by irradiating the outside of the capsule by X-rays or by optical laser irradiation, where in each case the highest uniformity of irradiation is sought. In this paper we consider the theoretical problem of irradiation of a capsule by point sources of X-rays, and seek configurations which maximise uniformity. By studying the root-mean-square deviation in terms of different order harmonic modes, we rationalise the dependence of uniformity on distance $d$ of the point sources from the centre of a capsule. After investigating simple configurations based on the Platonic solids, we use a global optimisation algorithm (basin-hopping) to seek better arrangements. The optimum configurations are found to depend strongly on $d$; at certain values which minimise nonuniformity, these involve grouping of sources on the vertices of octahedra or icosahedra, which we explain using a modal decomposition. The effect of uncertainties in both position and intensity is studied, and lastly we investigate the illumination of a capsule whose radius is changing with time.