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Register a new userProduction and decay of Sulphur excited species in a ECRIS plasma
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Authors
M.C. Martins
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The most important processes for the creation of S12+ to S14+ ions excited states from the ground configurations of S9+ to S14+ ions in an electron cyclotron resonance ion source, leading to the emission of K X-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double KL and triple KLL ionization, transition probabilities and energies for the deexcitation processes, are calculated in the framework of the multi-configuration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical K$alpha$ X-ray spectrum is obtained, which is compared to recent experimental data.
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We describe an apparatus designed to trap and cool a Yb and Cs mixture. The apparatus consists of a dual species effusive oven source, dual species Zeeman slower, magneto-optical traps in a single ultra-high vacuum science chamber, and the associated laser systems. The dual species Zeeman slower is used to load sequentially the two species into their respective traps. Its design is flexible and may be adapted for other experiments with different mixtures of atomic species. The apparatus provides excellent optical access and can apply large magnetic bias fields to the trapped atoms. The apparatus regularly produces 10${}^{8}$ Cs atoms at 13.3 $mu$K in an optical molasses, and 10${}^{9}$ Yb atoms cooled to 22 $mu$K in a narrowband magneto-optical trap.
A rigorous theoretical framework is developed for a generalized local frame transformation theory (GLFT). The GLFT is applicable to the following systems: to Rydberg atoms or molecules in an electric field, or to negative ions in any combination of electric and/or magnetic fields. A first test application to the photoionization spectra of Rydberg atoms in an external electric field demonstrates dramatic improvement over the first version of the local frame transformation theory developed initially by Fano and Harmin. This revised GLFT theory yields non-trivial corrections because it now includes the full on-shell Hilbert space without adopting the truncations in the original theory. Comparisons of the semi-analytical GLFT Stark spectra with {it ab initio} numerical simulations yields errors in the range of a few tens of MHz, an improvement over the original Fano-Harmin theory whose errors are 10-100 times larger. Our analysis provides a systematic pathway to precisely describe the corresponding photoabsorption spectra that should be accurate enough to meet most modern experimental standards.
We present results from a time dependent gas phase chemical model of a hot core based on the physical conditions of G305.2+0.2. While the cyanopolyyne HC_3N has been observed in hot cores, the longer chained species, HC_5N, HC_7N, and HC_9N have not been considered typical hot core species. We present results which show that these species can be formed under hot core conditions. We discuss the important chemical reactions in this process and, in particular, show that their abundances are linked to the parent species acetylene which is evaporated from icy grain mantles. The cyanopolyynes show promise as `chemical clocks which may aid future observations in determining the age of hot core sources. The abundance of the larger cyanopolyynes increase and decrease over relatively short time scales, ~10^2.5 years. We also discuss several sulphur bearing species. We present results from a non-LTE statistical equilibrium excitation model as a series of density, temperature and column density dependent contour plots which show both the line intensities and several line ratios. These aid in the interpretation of spectral line data, even when there is limited line information available.
Charge-breeding processes in Electron Cyclotron Resonance Ion Sources are numerically simulated by using the target helium plasma parameters obtained with NAM-ECRIS code. Breeding efficiency is obtained as a function of 1+ ion injection energy for some alkali ion beams. Time dependencies of extracted ions are calculated; typical times for reaching saturation in currents are in the range of few tens of milliseconds. Role of charge-exchange processes in breeding of ions is discussed. Recycling of ions on the source walls is shown to be important.
We study inelastic collisions between CaF molecules and $^{87}$Rb atoms in a dual-species magneto-optical trap. The presence of atoms increases the loss rate of molecules from the trap. By measuring the loss rates and density distributions, we determine a collisional loss rate coefficient $k_{2} = (1.43 pm 0.29) times 10^{-10}$ cm$^{3}$/s at a temperature of 2.4 mK. We show that this is not substantially changed by light-induced collisions or by varying the populations of excited-state atoms and molecules. The observed loss rate is close to the universal rate expected in the presence of fast loss at short range, and can be explained by rotation-changing collisions in the ground electronic state.
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