373 research outputs found
Negative-continuum dielectronic recombination into excited states of highly-charged ions
The recombination of a free electron into a bound state of bare, heavy
nucleus under simultaneous production of bound-electron--free-positron pair is
studied within the framework of relativistic first--order perturbation theory.
This process, denoted as "negative-continuum dielectronic recombination" leads
to a formation of not only the ground but also the singly- and doubly-excited
states of the residual helium-like ion. The contributions from such an
excited--state capture to the total as well as angle-differential
cross-sections are studied in detail. Calculations are performed for the
recombination of (initially) bare uranium U ions and for a wide range
of collision energies. From these calculations, we find almost 75 % enhancement
of the total recombination probability if the excited ionic states are taken
into account.Comment: 8 pages, 4 figures, accepted to PR
Many-electron effects on the x-ray Rayleigh scattering by highly charged He-like ions
The Rayleigh scattering of x-rays by many-electron highly charged ions is
studied theoretically. The many-electron perturbation theory, based on a
rigorous quantum electrodynamics approach, is developed and implemented for the
case of the elastic scattering of (high-energetic) photons by helium-like ion.
Using this elaborate approach, we here investigate the many-electron effects
beyond the independent-particle approximation (IPA) as conventionally employed
for describing the Rayleigh scattering. The total and angle-differential cross
sections are evaluated for the x-ray scattering by helium-like Ni,
Xe, and Au ions in their ground state. The obtained results
show that, for high-energetic photons, the effects beyond the IPA do not exceed
2% for the scattering by a closed -shell.Comment: 15 pages, 11 figure
Target effects in negative-continuum assisted dielectronic recombination
The process of recombination of a quasi-free electron into a bound state of
an initially bare nucleus with the simultaneous creation of a
bound-electron--free-positron pair is investigated. This process is called the
negative-continuum assisted dielectronic recombination (NCDR). In a typical
experimental setup, the initial electron is not free but bound in a light
atomic target. In the present work, we study the effects of the atomic target
on the single and double-differential cross sections of the positron production
in the NCDR process. The calculations are performed within the relativistic
framework based on QED theory, with accounting for the electron-electron
interaction to first order in perturbation theory. We demonstrate how the
momentum distribution of the target electrons removes the non-physical
singularity of the differential cross section which occurs for the initially
free and monochromatic electrons
Conceptual design of elliptical cavities for intensity and position sensitive beam measurements in storage rings
Position sensitive beam monitors are indispensable for the beam diagnostics
in storage rings. Apart from their applications in the measurements of beam
parameters, they can be used in non-destructive in-ring decay studies of
radioactive ion beams as well as enhancing precision in the isochronous mass
measurement technique. In this work, we introduce a novel approach based on
cavities with elliptical cross-section, in order to compensate for existing
limitations in ion storage rings. The design is aimed primarily for future
heavy ion storage rings of the FAIR project. The conceptual design is discussed
together with simulation results.Comment: Added definition of Uv and Pdiss in the introduction section. Added
Mode numbering in table 1 and figure 1 for more clarity. Corrected one wrong
figure reference. Other minor typo correction
Relativistic calculations of the x-ray emission following the Xe-Bi collision
We study the x-ray emission following the collision of a Bi ion with
a neutral Xe atom at the projectile energy 70 MeV/u. The collisional and
post-collisional processes are treated separately. The probabilities of various
many-electron processes at the collision are calculated within a relativistic
independent electron model using the coupled-channel approach with atomic-like
Dirac-Fock-Sturm orbitals. The analysis of the post-collisional processes
resulting in the x-ray emission is based on the fluorescence yields, the
radiation and Auger decay rates, and allows to derive intensities of the x-ray
emission and compare them with experimental data. A reasonable agreement
between the theoretical results and the recent experimental data is observed.
The role of the relativistic effects is investigated.Comment: 11 figures, 2 table
Relativistic calculations of the isotope shifts in highly charged Li-like ions
Relativistic calculations of the isotope shifts of energy levels in highly
charged Li-like ions are performed. The nuclear recoil (mass shift)
contributions are calculated by merging the perturbative and large-scale
configuration-interaction Dirac-Fock-Sturm (CI-DFS) methods. The nuclear size
(field shift) contributions are evaluated by the CI-DFS method including the
electron-correlation, Breit, and QED corrections. The nuclear deformation and
nuclear polarization corrections to the isotope shifts in Li-like neodymium,
thorium, and uranium are also considered. The results of the calculations are
compared with the theoretical values obtained with other methods.Comment: 28 page
Parity violation in the resonance elastic electron scattering on He-like uranium
Synopsis Parity violation on the cross section of the resonance elastic electron scattering by He-like uranium ion is studied. It is assumed that the incident electron is polarized and tuned in resonance with one of the close-lying opposite-parity states
HILITE – Ion Trap for Studies with Intense Laser Pulses
Synopsis We present our Penning Trap setup which is designed for capture, confinement and preparation of well-defined ion clouds for use in experiments with high-intensity lasers. We explain the experimental setup and the techniques used to capture, confine, manipulate and detect the ions inside the Penning trap. We give an over-view of the status of the project and the planned procedures to measure the laser-focus shape in situ
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