X射线汤姆孙散射在温稠密物质研究中的应用

温稠密物质(warm dense matter,WDM)是近年来兴起的一个前沿研究领域,它处于传统的凝聚态与等离子体状态之间的过渡状态.此状态下的物质广泛存在于宇宙和实验室中,如巨行星的内核、惯性约束聚变的内爆燃料等.然而人们对温稠密物质又是陌生的,因为传统的凝聚态和等离子体物理的理论和实验方法难以用于研究这样的物质状态.近几年,随着高功率激光装置以及诊断技术的发展,人们发展出X射线汤姆孙散射方法,对温稠密态物质开展了深入的研究,获得了重要的实验结果.     

X射线汤姆孙散射在温稠密物质研究中的应用

温稠密物质(warm dense matter,WDM)是近年来兴起的一个前沿研究领域,它处于传统的凝聚态与等离子体状态之间的过渡状态.此状态下的物质广泛存在于宇宙和实验室中,如巨行星的内核、惯性约束聚变的内爆燃料等.然而人们对温稠密物质又是陌生的,因为传统的凝聚态和等离子体物理的理论和实验方法难以用于研究这样的物质状态.近几年,随着高功率激光装置以及诊断技术的发展,人们发展出X射线汤姆孙散射方法,对温稠密态物质开展了深入的研究,获得了重要的实验结果.     

Observations of plasmons in warm dense matter

We present the first collective x-ray scattering measurements of plasmons in solid-density plasmas. The forward scattering spectra of a laser-produced narrow-band x-ray line from isochorically heated beryllium show that the plasmon frequency is a sensitive measure of the electron density. Dynamic structure calculations that include collisions and detailed balance match the measured plasmon spectrum indicating that this technique will enable new applications to determine the equation of state and compressibility of dense matter.     

Linear and nonlinear excitations in warm dense matter

Small and large amplitude linear and nonlinear ion acoustic and Langmuir waves are investigated for plasma with the generalized equation of state (EoS). This EoS covers a wide range of energy-density conditions from dilute classical regime up to the relativistically degenerate matter. Investigation shows that the linear dispersion and localized excitations of ion acoustic waves are significantly affected by the plasma parameters. It is also found that the criterion for ordinary soliton existence is significantly different for fully degenerate and nondegenerate plasma regimes with given electron temperature. In the nondegenerate regime, bright solitons form only for Mach numbers above a critical value which is only a function of the fluid temperature.     

Phase transitions in dense quark matter in a gravitational field of constant curvature

Abstact The impact of the gravitational field on the formation of quark and diquark condensate in the framework of the extended Nambu-Jona-Lasinio (NJL) model is studied. In the mean field approximation, an expression for the effective potential with regard to a finite temperature and density of quark matter in the static gravitational field of constant curvature is obtained. Original Russian Text ? V.Ch. Zhukovsky, A.V. Tyukov, D. Ebert, 2007, published in Vestnik Moskovskogo Universiteta. Fizika, 2007, No. 3, pp. 68–70.     

Exotica in dense and cold nuclear matter

A method for creating and investigating, under laboratory conditions, droplets of superdense cold matter is proposed, neutron stars being the closest analog of this kind of matter in nature. Arguments in support of the statement that an implementation of respective experiments is possible are presented, and the mechanism of kinematical cooling of the droplets in question is clarified. Various trigger types are proposed for performing searches for various exotic multiquark states in cold superdense matter.     

Phase transitions in hadronic matter

We formulate an equation of state for strongly interacting matter, which leads to a phase transition from massive resonance excitation to ideal gas behaviour. The structural similarity to the Van der Waals equation is discussed, as are extensions to describe hadron to quark matter transitions.     

Phase transitions in nuclear matter

The possible phases of nuclear matter are summarised. A new periodic phase of nuclear matter is discussed in details. In this phase the nucleon spin orientation follows the direction of the magnetic field associated with the periodic vector meson field. The probability of the transition accompanied by gamma radiation between this periodic phase and the anisotropic normal phase is derived.     

Aluminum equation-of-state data in the warm dense matter regime

Isochore measurements were performed in the warm dense matter regime. Pressure and internal energy variation of aluminum plasma (density 0.1 g/cm(3) and 0.3 g/cm(3)) are measured using a homogeneous and thermally equilibrated media produced inside an isochoric plasma closed vessel in the internal energy range 20-50 MJ/kg. These data are compared to detailed calculations obtained from ab initio quantum molecular dynamics, average atom model within the framework of the density functional theory, and standard theories. A dispersion between theoretical isochore equation of state is found in the studied experimental thermodynamic regime.     

Properties of warm dense matter at low entropies

We describe the qualitative properties of warm dense matter on adiabats, paying particular attention to their behavior in the vicinity of phase transitions. The equation of state of matter on the adiabat corresponding to an entropy of 1 k_B per nucleon is calculated within the compressible liquid drop model for nuclei.     

Excited electron dynamics modeling of warm dense matter

We present a model (the electron force field, or eFF) based on a simplified solution to the time-dependent Schr?dinger equation that with a single approximate potential between nuclei and electrons correctly describes many phases relevant for warm dense hydrogen. Over a temperature range of 0 to 100,000 K and densities up to 1 g/cm(3), we find excellent agreement with experimental, path integral Monte Carlo, and linear mixing equations of state, as well as single-shock Hugoniot curves from shock compression experiments. In principle eFF should be applicable to other warm dense systems as well.     

On phase transitions in cold nuclear matter

Real conditions for the formation of cold subhadronic matter are considered with allowance for nontrivial properties of the QCD vacuum. It is shown that a steady state of this matter is attainable, if at all, only in the case where dynamical (massive) quarks exist as rather stable quasiparticles. This state may consist of both a degenerate nearly perfect gas of these particles and a degenerate gas of current quarks in the interior of some (compact) neutron stars. In the latter case, both phases should coexist, and the first phase should occupy a certain space between the second phase and (normal) hadron matter occurring at the periphery of the star.     

Two- and three-color two-quark states in warm, dense quark matter

We study the Gaussian fluctuations of the two-flavor, meson-diquark bosonized NJL model for two and three colors at the color superconducting phase transition. The analysis is based on analytical properties of the polarization matrix. Pionic fluctuations are shown to be stabilised in the 2SC phase compared to the two-color result where they are right on threshold.     

Confining but chirally symmetric dense and cold matter

The possibility for existence of cold, dense chirally symmetric matter with confinement is reviewed. The answer to this question crucially depends on the mechanism of mass generation in QCD and interconnection of confinement and chiral symmetry breaking. This question can be clarified from spectroscopy of hadrons and their axial properties. Almost systematical parity doubling of highly excited hadrons suggests that their mass is not related to chiral symmetry breaking in the vacuum and is approximately chirally symmetric. Then there is a possibility for existence of confining but chirally symmetric matter. We clarify a possible mechanism underlying such a phase at low temperatures and large density. Namely, at large density the Pauli blocking prevents the gap equation to generate a solution with broken chiral symmetry. However, the chirally symmetric part of the quark Green function as well as all color non-singlet quantities are still infrared divergent, meaning that the system is with confinement. A possible phase transition to such a matter is most probably of the first order. This is because there are no chiral partners to the lowest lying hadrons.     

Equation of state for aluminum in warm dense matter regime

A semi-empirical equation of state model for aluminum in a warm dense matter regime is constructed. The equation of state, which is subdivided into a cold term, thermal contributions of ions and electrons, covers a broad range of phase diagram from solid state to plasma state. The cold term and thermal contribution of ions are from the Bushman–Lomonosov model, in which several undetermined parameters are fitted based on equation of state theories and specific experimental data. The Thomas–Fermi–Kirzhnits model is employed to estimate the thermal contribution of electrons. Some practical modifications are introduced to the Thomas–Fermi–Kirzhnits model to improve the prediction of the equation of state model. Theoretical calculation of thermodynamic parameters, including phase diagram, curves of isothermal compression at ambient temperature, melting, and Hugoniot, are analyzed and compared with relevant experimental data and other theoretical evaluations.     

Extreme ultraviolet interferometry of warm dense matter in laser plasmas

We demonstrate that interferometric probing with extreme ultraviolet (EUV) laser light enables determination of the degree of ionization of the "warm dense matter" produced between the critical and ablation surfaces of laser plasmas. Interferometry has been utilized to measure both transmission and phase information for an EUV laser beam at the photon energy of 58.5 eV, probing longitudinally through laser-irradiated plastic (parylene-N) targets (thickness 350 nm) irradiated by a 300 ps duration pulse of wavelength 438 nm and peak irradiance 10(12) W cm(-2). The transmission of the EUV probe beam provides a measure of the rate of target ablation, as ablated plasma becomes close to transparent when the photon energy is less than the ionization energy of the predominant ion species. We show that refractive indices η below the solid parylene N (η(solid) = 0.946) and expected plasma values are produced in the warm dense plasma created by laser irradiation due to bound-free absorption in C(+).     

Phase transitions in nucleonic matter and neutron-star cooling

A new scenario for neutron-star cooling is suggested by the correspondence between pion condensation, induced by critical spin-isospin fluctuations, and the metal-insulator phase transition in a 2D electron gas. Above the threshold density for pion condensation, the neutron single-particle spectrum acquires an insulating gap that quenches neutron contributions to neutrino production. In the liquid phase just below the transition, the fluctuations play dual roles by (i) creating a multisheeted neutron Fermi surface that extends to low momenta and activates the normally forbidden direct Urca cooling mechanism, and (ii) amplifying the nodeless P-wave neutron superfluid gap while suppressing S-wave pairing. Lighter stars without a pion-condensed core undergo slow cooling, whereas enhanced cooling occurs in heavier stars via direct Urca emission from a thin shell of the interior.     

激光产生温稠密物质的微观动力学过程及状态诊断

随着大型激光装置的建立和精密测量技术的发展,强激光与固体相互作用成为实验室产生温稠密物质的一个重要手段。温稠密物质的结构复杂性、瞬态性和非平衡性给理论建模和实验测量带来了巨大挑战。本文系统介绍了激光产生温稠密物质的实验手段和理论模拟方法方面的重要进展,分析了其中的电子激发动力学、电子-离子能量弛豫过程、离子动力学等物理过程,总结了温稠密物质状态诊断的实验技术和理论方法,并论述了激光产生温稠密物质的发展趋势。