arXiv subjects

H. E. De Witt

Publications and source records attributed to H. E. De Witt.

3 recordsLinked to original sources

arXiv2009

Corrections to linear mixing in binary ionic mixtures and plasma screening at zero separation

Using the results of extensive Monte Carlo simulations we discuss corrections to the linear mixing rule in strongly coupled binary ionic mixtures. We analyze the plasma screening function at zero separation, H_{jk}(0), for two ions (of types j=1,2 and k=1,2) in a strongly coupled binary mixture. The function H_{jk}(0) is estimated by two methods: (1) from the difference of Helmholtz Coulomb free energies at large and zero separations; (2) by fitting the Widom expansion of H_{jk}(x) in powers of interionic distance x to Monte Carlo data on the radial pair distribution function g_{jk}(x). These methods are shown to be in good agreement. For illustration, we analyze the plasma screening enhancement of nuclear burning rates in dense stellar matter.

physics.plasm-ph↗

arXiv2009

Nuclear fusion reaction rates for strongly coupled ionic mixtures

We analyze the effect of plasma screening on nuclear reaction rates in dense matter composed of atomic nuclei of one or two types. We perform semiclassical calculations of the Coulomb barrier penetrability taking into account a radial mean field potential of plasma ions. The mean field potential is extracted from the results of extensive Monte Carlo calculations of radial pair distribution functions of ions in binary ionic mixtures. We calculate the reaction rates in a wide range of plasma parameters and approximate these rates by an analytical expression that is expected to be applicable for multicomponent ions mixtures. Also, we analyze Gamow-peak energies of reacting ions in various nuclear burning regimes. For illustration, we study nuclear burning in C-O mixtures.

astro-ph.SR↗

arXiv1999

Coulomb crystals in the harmonic lattice approximation

The dynamic structure factor ${\tilde S}({\bf k},ω)$ and the two-particle distribution function $g({\bf r},t)$ of ions in a Coulomb crystal are obtained in a closed analytic form using the harmonic lattice (HL) approximation which takes into account all processes of multi-phonon excitation and absorption. The static radial two-particle distribution function $g(r)$ is calculated for classical ($T \gtrsim \hbar ω_p$, where $ω_p$ is the ion plasma frequency) and quantum ($T \ll \hbar ω_p$) body-centered cubic (bcc) crystals. The results for the classical crystal are in a very good agreement with extensive Monte Carlo (MC) calculations at $1.5 \lesssim r/a \lesssim 7$, where $a$ is the ion-sphere radius. The HL Coulomb energy is calculated for classical and quantum bcc and face-centered cubic crystals, and anharmonic corrections are discussed. The inelastic part of the HL static structure factor $S''(k)$, averaged over orientations of wave-vector {\bf k}, is shown to contain pronounced singularities at Bragg diffraction positions. The type of the singularities is different in classical and quantum cases. The HL method can serve as a useful tool complementary to MC and other numerical methods.

physics.plasm-ph↗