arXiv subjects

Carsten Fortmann

Publications and source records attributed to Carsten Fortmann.

6 recordsLinked to original sources

arXiv2010

Cluster virial expansion for the equation of state of partially ionized hydrogen plasma

We study the contribution of electron-atom interaction to the equation of state for partially ionized hydrogen plasma using the cluster-virial expansion. For the first time, we use the Beth-Uhlenbeck approach to calculate the second virial coefficient for the electron-atom (bound cluster) pair from the corresponding scattering phase-shifts and binding energies. Experimental scattering cross-sections as well as phase-shifts calculated on the basis of different pseudopotential models are used as an input for the Beth-Uhlenbeck formula. By including Pauli blocking and screening in the phase-shift calculation, we generalize the cluster-virial expansion in order to cover also near solid density plasmas. We present results for the electron-atom contribution to the virial expansion and the corresponding equation of state, i.e. pressure, composition, and chemical potential as a function of density and temperature. These results are compared with semi-empirical approaches to the thermodynamics of partially ionized plasmas. Avoiding any ill-founded input quantities, the Beth-Uhlenbeck second virial coefficient for the electron-atom interaction represents a benchmark for other, semi-empirical approaches.

physics.plasm-ph↗

arXiv2009

The influence of local field corrections on Thomson scattering in non-ideal two-component plasmas

Thomson scattering in non-ideal (collision-dominated) two-component plasmas is calculated accounting for electron-ion collisions as well as electron-electron correlations. This is achieved by using a novel interpolation scheme for the electron-electron response function generalizing the traditional Mermin approach. Also, ions are treated as randomly distributed inert scattering centers. The collision frequency is taken as a dynamic and complex quantity and is calculated from a microscopic quantum-statistical approach. Implications due to different approximations for the electron-electron correlation, i.e. different forms of the OCP local field correction, are discussed.

physics.plasm-ph↗

arXiv2008

Single-particle spectral function for the classical one-component plasma

The spectral function for an electron one-component plasma is calculated self-consistently using the GW0 approximation for the single-particle self-energy. In this way, correlation effects which go beyond the mean-field description of the plasma are contained, i.e. the collisional damping of single-particle states, the dynamical screening of the interaction and the appearance of collective plasma modes. Secondly, a novel non-perturbative analytic solution for the on-shell GW0 self-energy as a function of momentum is presented. It reproduces the numerical data for the spectral function with a relative error of less than 10% in the regime where the Debye screening parameter is smaller than the inverse Bohr radius, kappa<1/a_B. In the limit of low density, the non-perturbative self-energy behaves as n^(1/4), whereas a perturbation expansion leads to the unphysical result of a density independent self-energy [W. Fennel and H. P. Wilfer, Ann. Phys. Lpz._32_, 265 (1974)]. The derived expression will greatly facilitate the calculation of observables in correlated plasmas (transport properties, equation of state) that need the spectral function as an input quantity. This is demonstrated for the shift of the chemical potential, which is computed from the analytical formulae and compared to the GW0-result. At a plasma temperature of 100 eV and densities below 10^21 cm^-3, both approaches deviate less than 10% from each other.

physics.plasm-ph↗

arXiv2008

Self-consistent Spectral Function for Non-Degenerate Coulomb Systems and Analytic Scaling Behaviour

Novel results for the self-consistent single-particle spectral function and self-energy are presented for non-degenerate one-component Coulomb systems at various densities and temperatures. The GW^0-method for the dynamical self-energy is used to include many-particle correlations beyond the quasi-particle approximation. The self-energy is analysed over a broad range of densities and temperatures (n=10^17/cm^3-10^27/cm^3, T=10^2 eV/k_B-10^4 eV/k_B). The spectral function shows a systematic behaviour, which is determined by collective plasma modes at small wavenumbers and converges towards a quasi-particle resonance at higher wavenumbers. In the low density limit, the numerical results comply with an analytic scaling law that is presented for the first time. It predicts a power-law behaviour of the imaginary part of the self-energy, Im Sigma ~ -n^(1/4). This resolves a long time problem of the quasi-particle approximation which yields a finite self-energy at vanishing density.

physics.plasm-ph↗

arXiv2007

On the occurrence of Balmer spectra in expanding microplasmas from laser irradiated liquid hydrogen

Balmer spectra are investigated which are obtained from hydrogen droplets irradiated by ultra-short intense laser pulses. A unified quantum statistical description of bremsstrahlung, the Stark broadening and the van der Waals profile of hydrogen spectral lines is used, which allows to include many-particle effects. Analyzing the line profiles, a low ionization degree of a dense plasma is inferred, where the main contribution to the spectral line shape originates from the interaction with the neutral components. Effective temperatures and densities of the radiating microplasma are deduced. A dynamical description is given within plasma hydrodynamics, explaining the formation of excited atomic states in the expanding system and the occurrence of the observed Balmer lines only below a critical density.

physics.plasm-ph↗

arXiv2006

Optical properties and one-particle spectral function in non-ideal plasmas

A basic concept to calculate physical features of non-ideal plasmas, such as optical properties, is the spectral function which is linked to the self-energy. We calculate the spectral function for a non-relativistic hydrogen plasma in $GW$-approximation. In order to go beyond $GW$ approximation, we include self-energy and vertex correction to the polarization function in lowest order. Partial compensation is observed. The relation of our approach to $GW$ and $GWΓ$ calculations in other fields, such as the band-structure calculations in semiconductor physics, is discussed. From the spectral function we derive the absorption coefficient due to inverse bremsstrahlung via the polarization function. As a result, a significant reduction of the absorption as compared to the Bethe-Heitler formula for bremsstrahlung is obtained.

physics.plasm-ph↗