arXiv subjects

H. Reinholz

Publications and source records attributed to H. Reinholz.

9 recordsLinked to original sources

arXiv2017

Relaxation and Collective Excitations of Cluster Nano-Plasmas

Nano-plasmas produced, e.g. in clusters after short-pulse laser irradiation, can show collective excitations as derived from the time evolution of fluctuations in thermodynamic equilibrium. Molecular dynamical simulations are performed for various cluster sizes. New data are obtained for the minimum value of the stationary cluster charge. The bi-local auto-correlation function gives the spatial structure of the eigenmodes, for which energy eigenvalues are obtained. Varying the cluster size, starting from a few-particles cluster, the emergence of macroscopic properties like collective excitations is shown.

physics.plasm-ph↗

arXiv2016

Optical conductivity of warm dense matter in wide frequency range within quantum statistical and kinetic approach

Fundamental properties of warm dense matter are described by the dielectric function, which gives access to the frequency-dependent electrical conductivity, absorption, emission and scattering of radiation, charged particles stopping and further macroscopic properties. Different approaches to the dielectric function and the related dynamical collision frequency are compared in a wide frequency range. The high-frequency limit describing inverse bremsstrahlung and the low-frequency limit of the dc conductivity are considered. Sum rules and Kramers-Kronig relation are checked for the generalized linear response theory and the standard approach following kinetic theory. The results are discussed in application to aluminum, xenon and argon plasmas.

physics.plasm-ph↗

arXiv2015

Warm dense matter conductivity including electron-electron collisions

The controversy with respect to the role of electron-electron collisions in the dynamic conductivity of dense plasmas is resolved. In particular, the dc conductivity is analyzed in the low-density, non-degenerate limit where the Spitzer theory is valid and electron-electron collisions lead to the well-known reduction of the result for a Lorentz plasma. With increasing degeneracy, the contribution of electron-electron collisions to the dc conductivity is decreasing and can be neglected for the liquid metal domain where the Ziman-Faber theory is applicable. We show how electron-electron collisions have to be implemented in calculations based on the Kubo-Greenwood formula which is prevalently applied in simulations for the frequency-dependent conductivity in the warm dense matter region, i.e. for arbitrary degeneracy.

physics.plasm-ph↗

arXiv2014

Cluster virial expansion and electron-hydrogen molecule scattering

The equation of state of partially ionized hydrogen plasma is considered with special focus on the contribution of $e-\rm H_2$ interaction. Within a cluster virial expansion, the Beth-Uhlenbeck formula is applied to infer the contribution of bound and scattering states to the temperature dependent second virial coefficient. The scattering states are calculated using the phase expansion method with the polarization interaction model that incorporates experimental data for the $e-\rm H_2$ scattering cross section. We present results for the scattering phase shifts, differential scattering cross sections, the second virial coefficient due to $e-\rm H_2$ interaction. The influence of this interaction on the composition of the partially ionized hydrogen plasma is confined to the parameter range where both the $\rm H_2$ and the free electron components are abundant.

physics.plasm-ph↗

arXiv2008

The influence of Pauli blocking effects on the properties of dense hydrogen

We investigate the effects of Pauli blocking on the properties of hydrogen at high pressures, where recent experiments have shown a transition from insulating behavior to metal-like conductivity. Since the Pauli principle prevents multiple occupation of electron states (Pauli blocking), atomic states disintegrate subsequently at high densities (Mott effect). We calculate the energy shifts due to Pauli blocking and discuss the Mott effect solving an effective Schroedinger equation for strongly correlated systems. The ionization equilibrium is treated on the basis of a chemical approach. Results for the ionization equilibrium and the pressure in the region 4.000 K < T < 20.000 K are presented. We show that the transition to a highly conducting state is softer than found in earlier work. A first order phase transition is observed at T < 6.450 K, but a diffuse transition appears still up to 20.000 K.

physics.plasm-ph↗

arXiv2006

Bremsstrahlung vs. Thomson scattering in VUV-FEL plasma experiments

We determine the spectral photon yield from a hot dense plasma irradiated by VUV-FEL light in a Thomson scattering experiment. The Thomson signal is compared to the emission background mainly caused by bremsstrahlung photons. We determine experimental conditions that allow for a signal-to-background ratio larger than unity. By derivation of the Thomson and the bremsstrahlung spectrum from linear response theory we present a consistent quantum statistical approach to both processes. This allows for a systematic treatment of medium and quantum effects such as dynamical screening and strong collisions. Results are presented for the threshold FEL-intensity as a function of density and temperature. We show that the account for quantum effects leads to larger thresholds as compared to previous work.

physics.plasm-ph↗

arXiv2005

Bremsstrahlung from dense plasmas and the Landau-Pomeranchuk-Migdal effect

The suppression of the bremsstrahlung cross section due to multiple scattering of the emitting electrons is an important effect in dense media (Landau-Pomeranchuk-Migdal effect). Here, we study the emission from a dense, fully-ionized and non-relativistic hydrogen plasma. Using the dielectric approach, we relate optical properties such as emission and absorption to equilibrium force-force correlation functions, which allow for a systematic perturbative treatment with the help of thermodynamic Green functions. By considering self-energy and vertex corrections, medium modifications such as multiple scattering of the emitting electrons are taken into account. Results are presented for the absorption coefficient as a function of the frequency at various densities. It is shown that the modification of the inverse bremsstrahlung due to medium effects becomes more significant in the low frequency and high density region.

physics.plasm-ph↗

arXiv2004

Internal vs. External Conductivity of a Dense Plasma: Many-particle theory and simulations

In the long-wavelength limit k=0, the response function has been investigated with respect to the external and internal fields which is expressed by the external and internal conductivity, respectively. Molecular dynamics (MD) simulations are performed to obtain the current-current correlation function and the dynamical collision frequency which are compared with analytical expressions. Special attention is given to the dynamical collision frequency and the description of plasma oscillations in the case of k=0. The relation between the external and internal conductivity and to the current-current correlation function is analyzed.

physics.plasm-ph↗

arXiv2002

Reflectivity of Shock Compressed Xenon Plasma

Experimental results for the reflection coefficient of shock-compressed dense Xenon plasmas at pressures of 1.6 - 17 GPa and temperatures around 30 000 K using a laser beam with λ= 1.06 10^-6 m are compared with calculations based on different theoretical approaches to the dynamical collision frequency. It is found that a reasonable description can be given assuming a spatial electron density profile corresponding to a finite width of the shock wave front of about $2 10^-6 m.

physics.plasm-ph↗