Ionospheric simulator survey

Evaluation of D and E region ionospheric simulation technique

Coincident Charge State Production In F⁶⁺+Ne Collisions

Total cross sections are presented for the production of various stages of multiple ionization of the target in coincidence with the final projectile charge state for collisions of F6+ with Ne at 10 and 15 MeV. In particular, the current measurements are compared with the results of a classical trajectory Monte Carlo method in which electrons are included explicitly on both target and projectile (nCTMC) and with those based on the conventional independent electron model (IEM). It is shown by the good agreement with experiment that the nCTMC model simultaneously represents well the ionization, charge transfer and excitation channels for both target and projectile. Further, it is demonstrated that the IEM is in clear disagreement with the present experiment and is inadequate to predict the outcome of such multi-electronic transition processes. However, the IEM is shown to provide a reasonable estimate of the free electron production, that is, the cross section summed over charge states weighted by the number of electrons liberated. The IEM is also used to illustrate a process in cusp electron production where electrons are interchanged between the target and projectile. © 1990, IOP Publishing Ltd

Large-angle Scattering In Positron-helium And Positron-krypton Collisions

We have calculated differential cross sections as a function of the projectile scattering angle for positron-helium and positron-krypton collisions using the classical-trajectory Monte Carlo technique. These intermediate- velocity collisions have been simulated by various independent-electron and n-electron models, using both screened Coulomb and quantum model potentials to approximate the effects of electron-electron interactions. These several models all indicate that scattering of positrons to large angles in ionizing collisions persists to high impact velocities. In a previous work [Phys. Rev. A 38, 1866 (1988)] we proposed that the recent experiments that have measured the total cross section for positronium formation could be affected by the loss of positron flux due to incomplete confinement after large-angle scattering. Here, utilizing these newly calculated differential-scattering cross sections, adjustments are computed that account for the difference between the experimental and theoretical behaviors of the positronium formation cross section. Further, it is demonstrated that large angle scattering in the elastic channel is important for one of the experiments. We have also computed total cross sections for ionization and charge transfer for collisions of protons with krypton. Good agreement is obtained in these cases with experimental measurements. © 1989 The American Physical Society

Classical Calculation Of High-energy Electron Capture In 5-MeV Proton-hydrogen Collisions

The existence of the classical Thomas peak in the angular distribution of projectiles undergoing capture in collisions of 5-MeV protons with atomic hydrogen is explored using the three-body, three-dimensional classical-trajectory Monte Carlo technique. A method that selects only that portion of the initial phase space which yields capture at this energy was developed to make the calculation tractable due to the extremely small cross section. The spectrum obtained displays only a small shoulder near the angle predicted by Thomas on the basis of successive classical binary collisions and the total (integral) cross section is overestimated by a factor of 26 compared to recent experimental measurements. The overestimation originates from too large a contribution from velocity matching direct capture; the energy regime in which it is significant is discussed. In addition, the double-scattering events in this model which contribute significantly to the cross sections are found to differ substantially from the Thomas picture. © 1992 The American Physical Society

Recent Advances In The Comparison Of Matter— And Antimatter—atom Collisions

The relatively recent advent of low energy antimatter projectiles has spurred a rapid advance in the comparison of matter- and antimatter-atom collisions. These experimental studies have in turn stimulated a great deal of theoretical effort to explain their results, and together both theory and experiment have shed new light on the dynamics of ion-atom collisions. Here we review these developments with particular emphasis on the processes of ionization and charge transfer. © 1991 IOP Publishing Ltd

Workshop on Meteorites From Cold and Hot Deserts

The current workshop was organized to address the following points: (1) definition of differences between meteorites from Antarctica, hot deserts, and modern falls; (2) discussion of the causes of these differences; (3) implications of possible different parent populations, infall rates, weathering processes, etc.; (4) collection, curation, and distribution of meteorites; and (5) planning and coordination of future meteorite searches

Feq⁺+ H, H2and He Electron Loss And He2++ H(N = 1, 2) Electron Capture Cross Sections: Processes Of Interest In Fusion Plasmas

Cross sections have been calculated utilizing the classical trajectory Monte Carlo method for collisional processes of special interest to plasma fusion research. Specifically, H1H2and He total electron loss cross sections for the impact by Feq+(1 \u3c q \u3c 26) impurity ions, in the energy range of 50 to 500keV/u, are presented. These results illustrate a clear departure for low charge states (q \u3c 10) from scaling of the cross section with projectile charge (q). Further, cross sections for electron capture from both the ground and n = 2 states of H by 30 to lOOkeV/u He2+impact are tabulated as function of final n-level, yielding information for neutral beam heating models. © 1991 IOP Publishing Ltd

Differential Cross Sections For State-selective Electron Capture In 25100-keV Proton-helium Collisions

Cross sections differential in the scattering angle of the projectile are presented for electron capture summed over all states and to the 2s, 2p, 3s, 3p, 4s, and 4p states of hydrogen in 25-, 50-, and 100-keV proton-helium collisions. The classical-trajectory Monte Carlo (CTMC) technique was employed for these calculations as well as to compute total cross sections as a function of impact energy. The latter are compared with experiment to display the behavior of the integral state-selective cross sections in this energy regime. Detailed comparison is also made between the calculated angular differential cross sections and the experimental measurements of Martin et al. [Phys. Rev. A 23, 285 (1981)] for capture summed over all states and of Seely et al. [Phys. Rev. A 45, R1287 (1992)] for capture to the 2p state. Very good overall agreement is found. Regarding the cross section for capture summed over all states, an improved agreement is demonstrated by using an alternate representation of the initial state in the CTMC method, which improves the electronic radial distribution, but which cannot presently be applied to state-selective determinations. © 1992 The American Physical Society

Deep Level Transient Spectroscopy in Quantum Dot Characterization

Deep level transient spectroscopy (DLTS) for investigating electronic properties of self-assembled InAs/GaAs quantum dots (QDs) is described in an approach, where experimental and theoretical DLTS data are compared in a temperature-voltage representation. From such comparative studies, the main mechanisms of electron escape from QD-related levels in tunneling and more complex thermal processes are discovered. Measurement conditions for proper characterization of the levels by identifying thermal and tunneling processes are discussed in terms of the complexity resulting from the features of self-assembled QDs and multiple paths for electron escape