Probing the classical field approximation-thermodynamics and decaying vortices

Harry Schmidt, Krzysztof Góra, Filip Floegel, Mariusz Gajda and Kazimierz Rzazewski

We review our version of the classical field approximation to the dynamics of a finite-temperature Bose gas. In the case of a periodic box potential, we investigate the role of the high-momentum cut-off, essential in the method. In particular, we show that the cut-off going to the infinity limit describes the particle number going to infinity with the scattering length going to zero. In this weak-interaction limit, the relative population of the condensate tends to unity. We also show that the cross-over energy, at which the probability distribution of the condensate occupation changes its character, grows with a growing scattering length. In the more physical case of the condensate in the harmonic trap we investigate the dissipative dynamics of a vortex. We compare the decay time and the velocities of the vortex with the available analytic estimates.

J. Opt. B: Quantum Semiclass. Opt. vol. 5, S1-S7 (2003)

Scattering of sulfur ions carbon: Classical-trajectory Monte Carlo results

We analyze classically the scattering of sulfur ions by carbon using the classical-trajectory Monte Carlo method. It is assumed that the scatterer and scattered nuclei are coupled to each other as well as to all electrons, but there is no coupling between electrons themselves. To initialize the state of both atoms, quasiexact energies are used that are obtained from the Dirac-Fock method. Effective charges are used to partially take into account the intra-atomic interactions between electrons. We concentrate on the cross sections for production of vacancies in the K and L shells and capture of electrons to K, L, and M shells of the sulfur ions. The dependence of these cross sections on the energy of the projectile sulfur ions and on the initial charge states of these ions is analyzed. Our results will be helpful in the interpretation of x-ray spectra from highly ionized fast sulfur projectiles passing through a carbon foil.

Phys. Rev. A vol. 67, 012713-1-10 (2003) Slabkowska, Katarzyna, Polasik Marek, Janowicz Maciej