419 research outputs found
Double lepton pair production with electron capture in relativistic heavy--ion collisions
We present a theoretical study of a double lepton pair production in
ultra--relativistic collision between two bare ions. Special emphasis is placed
to processes in which creation of (at least one) pair is accompanied
by the capture of an electron into a bound ionic state. To evaluate the
probability and cross section of these processes we employ two approaches based
on (i) the first--order perturbation theory and multipole expansion of Dirac
wavefunctions, and (ii) the equivalent photon approximation. With the help of
such approaches, detailed calculations are made for the creation of two
bound--free pairs as well as of bound--free and free--free
pairs in collisions of bare lead ions Pb. The results of
the calculations indicate that observation of the double lepton processes may
become feasible at the LHC facility.Comment: 12 pages, 1 figur
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
Proton and heavy ion acceleration by stochastic fluctuations in the Earth's magnetotail
Abstract. Spacecraft observations show that energetic ions are found in the Earth's magnetotail, with energies ranging from tens of keV to a few hundreds of keV. In this paper we carry out test particle simulations in which protons and other ion species are injected in the Vlasov magnetic field configurations obtained by Catapano et al. (2015). These configurations represent solutions of a generalized Harris model, which well describes the observed profiles in the magnetotail. In addition, three-dimensional time-dependent stochastic electromagnetic perturbations are included in the simulation box, so that the ion acceleration process is studied while varying the equilibrium magnetic field profile and the ion species. We find that proton energies of the order of 100 keV are reached with simulation parameters typical of the Earth's magnetotail. By changing the ion mass and charge, we can study the acceleration of heavy ions such as He+ + and O+, and it is found that energies of the order of 100–200 keV are reached in a few seconds for He+ + , and about 100 keV for O+
Wave-particle interactions in the outer radiation belts
Data from the Van Allen Probes have provided the first extensive evidence of
non-linear (as opposed to quasi-linear) wave-particle interactions in space
with the associated rapid (fraction of a bounce period) electron acceleration
to hundreds of keV by Landau resonance in the parallel electric fields of time
domain structures (TDS) and very oblique chorus waves. The experimental
evidence, simulations, and theories of these processes are discussed. {\bf Key
words:} the radiation belts, wave-particle interaction, plasma waves and
instabilitiesComment: 9 pages, 2 figure
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