High Energy Density Physics最新文献

We describe laboratory experiments to generate x-ray photoionized plasmas of relevance to accretion-powered x-ray sources such as neutron star binaries and quasars, with significant improvements over previous work. A key quantity is referenced, namely the photoionization parameter, defined as $\xi =4\pi F/n_e$ where F is the x-ray flux and n_e the electron density. This is normally meaningful in an astrophysical steady-state context, but is also commonly used in the literature as a figure of merit for laboratory experiments that are, of necessity, time-dependent. We demonstrate emission-weighted values of $\xi >50$ erg-cm s⁻¹ using laser-plasma x-ray sources, with higher results at the centre of the plasma which are in the regime of interest for several astrophysical scenarios. Comparisons of laboratory experiments with astrophysical codes are always limited, principally by the many orders of magnitude differences in time and spatial scales, but also other plasma parameters. However useful checks on performance can often be made for a limited range of parameters. For example, we show that our use of a keV line source, rather than the quasi-blackbody radiation fields normally employed in such experiments, has allowed the generation of the ratio of inner-shell to outer-shell photoionization expected from a blackbody source with ∼keV spectral temperature. We compare calculations from our in-house plasma modelling code with those from Cloudy and find moderately good agreement for the time evolution of both electron temperature and average ionisation. However, a comparison of code predictions for a K-β argon X-ray spectrum with experimental data reveals that our Cloudy simulation overestimates the intensities of more highly ionised argon species. This is not totally surprising as the Cloudy model was generated for a single set of plasma conditions, while the experimental data are spatially integrated.

The photoionized plasma gas cell experiment is an established platform we use to make at-parameter ($\xi >>1{\mathrm{ergs\; cm\; s}}^{-1}$) measurements of plasma properties with application to high-energy astrophysical systems. We model the experiments with 1D radiation hydrodynamics simulations using the HELIOS-CR code to inform our understanding and assist in the interpretation of results. The simulations predict that the bulk of the plasma is in a quasi-uniform and hydrodynamically unperturbed state throughout the duration of the experiment. To evaluate this prediction, we introduced a photonic Doppler velocimetry (PDV) diagnostic to measure spatially and temporally resolved plasma electron density. The initial measurements were successful but had limitations that made model-data comparisons challenging. To address this, we re-designed the gas cell PDV diagnostic and doubled the number of measurement locations to sample across two thirds of the depth of the cell. We also present a comparison of the results from the upgraded PDV diagnostic to the HELIOS-CR simulations for the first time. The experimental data confirms the prediction of an unperturbed region in the bulk of the plasma but reveals discrepancies in the time evolution and spatial distribution of the simulated electron density.

The phenomenon of ball lightning anomalous penetration through thick metalic absorbing filters and appearance of a dark ball lightning has been investigated. The ball lightning represents an extreme state of ionized matter in Nature. At the interaction of ball lightning with a dense medium a process of energy conversion of its own poloidal magnetic field into the kinetic energy of its charged particles occurs. The phenomenon of anomalous passage of a ball lightning within the standard model can be explained only by cascading generation of particles due to interaction of high-energy protons with an absorbing filter. The decay of pions leads either to the appearance of negative muons and muon antineutrino or positive muons and muon neutrino. This fact is confirmed by the absence of any particle imprints on the surface of this filter and the presence of a high potential of variable polarity in the region above the absorber after passing a ball lightning through it. This phenomenon of muons generation can be used to solve the problem of nuclear fusion.

The purpose of this paper is to illustrate our contribution to general plasma physics studies obtained since the 90s with multiple versions and adaptations of the classical molecular dynamics (CMD) simulation interactive code called BinGo. After a description of the particulars of the CMD simulation models and the BinGo code suite, some applications are discussed for illustration. These results validate the CMD simulation as a powerful tool of investigation for hot dense plasmas.

In warm dense xenon, thermally excited and pressure-ionized electrons are essential for calculating the equation of state; however, the classical Thomas Fermi model is unsuitable for describing this state. Therefore it is necessary to find an appropriate theoretical model to express the thermal characteristics of electrons in warm dense Xe. In this study, we use the average atom-in-jellium(AJ) model to compute the contribution of thermally excited and pressure-ionized electrons of Xe over a wide range of temperatures and densities. The electron resonance state in the AJ model is treated by the adaptive mesh movement method. Moreover a method for correcting the cold pressure curve(which is used in the liquid phase calculations) in the AJ model is proposed. For the liquid phase, the ion motion contribution is expressed by the liquid perturbation theory of the corrected rigid-ion sphere model. For the solid phase, the ion motion contribution is described by the Debye model combined with anharmonic correction. Our calculated Hugoniot curve of Xe coincides with those of the experiments, first-principles density functional calculations and other theoretical models. The melting line of Xe is also consistent with the results of first-principle calculations and other theoretical models.

Supersonic heat (Marshak) waves are radiation dominated, and play an important role in inertial confinement fusion and in astrophysical and laboratory systems. Doping the foam with heavy metals with high opacity cause dramatic changing of the heat wave behavior by the changing of the material opacity. For that reason, the effects of doping on heat waves propagation in low density foams have been measured in a number of experiments reported in the literature. The present study uses the NIF facility advantages to overcome the two main problems that have been identified in earlier works: the radiation pre-heat; and the considerable experimental uncertainties in respect to the physical phenomena. The new experiment will be able to measure the coupling between opacity and the heat wave progress and evolution, because the heat wave progress in a doped foam is expected to be very similar to the heat wave progress in the pure foam, when the latter’s absorption cross-section is simply scale by multiplying with a constant factor.

We discuss the krypton He$\beta$ line spectrum including Li-like satellites with a spectator electron in n = 2 and n = 3 and detailed line shapes computed using standard Stark broadening theory for hot dense plasma conditions relevant to X-ray tracer spectroscopy of inertial confinement fusion implosion cores. The results show that the interference term in the electron broadening does not produce a significant effect for these satellite transitions. However, the effect of the electric field mixing of the energy levels driven by the ion’s microfield distribution does produce a significant change in the line shape. Level populations calculated with a collisional radiative atomic kinetics model were employed to obtain the photon energy resolved emissivity and opacity using the Stark line shapes, and the emergent intensity distribution was calculated by integrating the radiation transport equation along chords assuming a uniform spherical plasma source. The line spectrum has electron temperature ($T_e$) and density ($n_e$) sensitivity due to the temperature and density dependence of level populations and the density dependence of the Stark line shapes. Hence, this spectrum is suitable for a simultaneous temperature and density plasma diagnostic of implosion cores.

When calculating the spectral opacity of hot dense plasmas one often encounters the need to generate a list of detailed ionic configurations of bound states for each ion stage in the plasma. We present here a non-recursive algorithm for the efficient construction of such a list of states.

Experiments on the National Ignition Facility (NIF) have provided clear evidence of ablator material mixing into the Hot-Spot, leading to degraded performance. However, inferring the amount of mix and Hot-Spot conditions from typical experimental observations (e.g. x-ray spectra and images) is highly challenging. We have developed an analysis method that utilizes machine learning assisted Bayesian inference to find the probability distributions of the Hot-Spot and mix conditions. This approach uses a neural network, trained on an idealized 2-dimensional representation of the Hot-Spot and mix distribution, and Bayesian inference to find the statistical distributions of Hot-Spot conditions that provide a match with observations. We have tested this method with synthetic data from simulations.