| 1. |
- Akram, Nadeem, 1980-
(författare)
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Transmission of slow highly charged ions through nano-structures
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on experimental investigations of transmitting slow highly charged ions through nano-structures of various cross-sections. Transmission through rhombic and rectangular nanocapillaries in muscovite and phlogopite mica, respectively, is used to study the guiding and shaping of highly charged ion beams. The two-dimensional angular distributions of the transmitted ions reveal that slow highly charged ion beams are tailored into rectangular and rhombic shapes after passing through the capillaries of rhombic and rectangular cross-sections, respectively. These transmission profiles are maintained for tilt angles within the geometrical opening angle of the capillaries. The ‘incident charge-dependent’ time evolution of the transmission profiles indicates that the tailored shape comes from the image force experienced by the traversing ions and the deposited charge by the incident ions moves the transmission profiles towards higher observation angles with respect to the beam direction. Transmission is also observed for tilt angles larger than the geometrical opening of the capillaries and evidence of charging-up of capillary walls was seen. Other incident charge-dependent features including the increase in angular width and shift of transmitted angular distributions were also observed. Starting from initially charged capillaries, it was found that the deposited charge must be distributed uniformly along the capillary walls to maintain the tailored rhombic shape through rectangular capillaries. In this thesis, a technique is presented which is successfully employed to investigate directly the formation of charge patches on the walls of a glass capillary by imaging the visible photons emitted due to impact of ions on the walls. These tapered glass capillaries were applied in biological studies of cell damage by ion impact and the technique provides a new way to directly observe the development of ion-guiding in these capillaries. With the help of this technique the mechanism of ion-guiding can be controlled and optimized. We also review the transmission characteristics of slow highly charged ions through nanometer thick foils and present the results of transmission of slow highly charged ions through ultra-thin carbon nano-sheets of molecular layer thickness. The observed energy loss is smaller than the calculated one using SRIM and agrees rather well with the Firsov model. The transmitted ions also keep their initial charge state up to 98% in a complete contradiction to the electron capture rate predicted by the classical over-the-barrier model. The results suggest that the energy loss of slow highly charged ions in such thin sheets is due to the electronic excitations, without charge exchange inside the target.
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| 2. |
- Akram, Nadeem, et al.
(författare)
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Transmission of slow highly charged ions through rectangular nanocapillaries
- 2014
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Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- Transmission of slow highly charged ions through rectangular nanocapillaries in phlogopite mica is studied. The transmission profiles have rhombic pattern at tilt angles within the geometrical opening angle of the capillaries. The time evolution of ion transmission reveals certain features contributing to the tailored transmission profiles.
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| 3. |
- Akram, Nadeem, 1980-, et al.
(författare)
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Transmission of slow highly charged ions through ultra-thin carbon nano-sheets
- 2011
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Ingår i: Proceedings of 3<sup>rd</sup> Int. Conf. on “Current developments in Atomic, Molecular, Optical and Nano Physics”.
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Konferensbidrag (refereegranskat)abstract
- Transmission properties of slow highly charged ions through nanometer thick foils are discussed. We also report on the measurement of the energy loss and the charge states of 46.2 keV Ne10+-ions and 11.7 keV Ne3+-ions transmitted through ultra-thin carbon nano-sheets. The sheets had a thickness of 1.2 nm (single molecular layer) and 3.6 nm (three molecular layers). The measured energy loss of the transmitted ions is considerably smaller than the calculated energy loss by SRIM but it is in agreement with energy loss calculated using the Firsov model. The majority of the transmitted ions retain their initial charge state (up to 98%) contrary to prediction by the classical over-the-barrier model. The results suggest that the energy loss of slow highly charged ions in such thin sheets is only due to the electronic excitations, without charge exchange inside the target.
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| 4. |
- Ali, Safdar, 1982-
(författare)
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Electron - Ion Recombination Data for Plasma Applications : Results from Electron Beam Ion Trap and Ion Storage Ring
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contains results of electron-ion recombination processes in atomic ions relevant for plasma applications. The measurements were performed at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) and at the CRYRING heavy-ion storage ring. Dielectronic recombination (DR) cross sections, resonant strengths, rate coefficients and energy peak positions in H-like and He-like S are obtained for the first time from the EBIT measurements. Furthermore, the experimentally obtained DR resonant strengths are used to check the behaviour of a scaling formula for low Z, H-and He-like iso-electronic sequences and to update the fitting parameters. KLL DR peak positions for initially He- to B-like Ar ions are obtained experimentally from the EBIT measurements. Both the results from highly charged sulfur and argon are compared with the calculations performed with a distorted wave approximation.Absolute recombination rate coefficients of B-like C, B-like Ne and Be-like F ions are obtained for the first time with high energy resolution from storage ring measurements. The experimental results are compared with the intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients of each of these ions are obtained by convoluting the energy dependent recombination spectra with a Maxwell-Boltzmann energy distribution in the temperature range of 103-106 K. The resulting plasma rate coefficients are presented and compared with the calculated data available in literature.
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| 5. |
- Ali, Safdar, et al.
(författare)
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Electron-ion recombination of H- and He-like sulfur
- 2011
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 44:22, s. 225203-
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Tidskriftsartikel (refereegranskat)abstract
- Electron-ion recombination of sulfur ions with electrons in the energy range of 1.6-3 keV was studied at the Stockholm Refrigerated Electron Beam Ion Trap. We obtained the KLn dielectronic recombination (DR) cross sections up to n = 5 for H-like and He-like sulfur ions by observing the x-rays from the trapped ions. A fully relativistic distorted wave approximation method was used for calculating the DR cross sections, while the resonance energies were obtained with a multiconfiguration Dirac-Fock approach using the GRASP II code. The calculations agree with the experimental results within the experimental error bars. Additionally, the obtained total DR resonance strengths were used to check the behaviour of a scaling formula for low-Z, He-like iso-electronic sequence (Watanabe et al 2001 J. Phys. B: At. Mol. Opt. Phys. 34 5095).
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| 6. |
- Ali, Safdar, et al.
(författare)
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Electron-ion recombination rate coefficients for C II forming C I
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 753:2, s. 132-
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Tidskriftsartikel (refereegranskat)abstract
- We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (∆n = 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 103-106 K. The derived temperature dependent plasma recombination rate coefficients are presented graphically to compare with the theoretical data available in literature and parameterized by using a fit formula for convenient use in plasma modelling codes. In the temperature range of 103-2×104 K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2×104 K the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.
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| 7. |
- Ali, Safdar, et al.
(författare)
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Experimental rate coefficients of F5+ recombining into F4
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 557
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Tidskriftsartikel (refereegranskat)abstract
- Recombination spectra of F5+ producing F4+ have been investigated with high-energy resolution, using the CRYRING heavy-ion storage ring. The absolute recombination rate coefficients are derived in the centre-of-mass energy range of 0-25 eV. The experimental results are compared with intermediate-coupling AUTOSTRUCTURE calculations for 2s-2p (Delta n = 0) core excitation and show very good agreement in the resonance energy positions and intensities. Trielectronic recombination with 2s(2)-2p(2) transitions are clearly identified in the spectrum. Contributions from F5+ ions in an initial metastable state are also considered. The energy-dependent recombination spectra are convoluted with Maxwell-Boltzmann energy distribution in the 10(3)-10(6) K temperature range. The resulting temperature-dependent rate coefficients are compared with theoretical results from the literature. In the 10(3)-10(4) K range, the calculated data significantly underestimates the plasma recombination rate coefficients. Above 8 x 10(4) K, our AUTOSTRUCTURE results and plasma rate coefficients from elsewhere show agreement that is better than 25% with the experimental results.
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| 8. |
- Ali, Safdar, et al.
(författare)
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Photo-recombination studies at R-EBIT with a Labview control and data = quisition system
- 2011
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 6, s. C01016-
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Tidskriftsartikel (refereegranskat)abstract
- Equipment at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) was developed for photo-recombination studies. A LabView-based event mode data acquisition and R-EBIT control system was implemented. The energies of KLL dielectronic recombination resonances in Li- to C-like argon ions were determined and compared with theoretical calculations performed using a distorted wave approximation. The theoretical and experimental peak positions for Li-, Be-, and C-like argon ions agree within the error bars. For B-like argon we observe an energy shift of 9 eV between the experimentally obtained peak position and the calculated result.
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| 9. |
- Grieser, M., et al.
(författare)
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Storage ring at HIE-ISOLDE Technical design report
- 2012
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Ingår i: The European Physical Journal Special Topics. - : Springer Science and Business Media LLC. - 1951-6355 .- 1951-6401. ; 207:1, s. 1-117
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Forskningsöversikt (refereegranskat)abstract
- We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report.
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| 10. |
- Gudmundsson, Magnus, et al.
(författare)
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Angular scattering in fast ion-atom electron transfer collisions : projectile wave diffraction and Thomas mechanisms
- 2010
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:18, s. 185209-
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Tidskriftsartikel (refereegranskat)abstract
- We report experimental angular differential cross sections for double-electron capture in He2+ + He collisions and single-electron capture in H+ + He collisions for the 1.3-12.5 MeV kinetic energy range. In all cases, the total cross sections are dominated by forward scattering peaks in d sigma/d Omega. The shapes and widths (but not the magnitudes) of these peaks are very similar for all energies and for capture of one or two electrons corresponding also to our measured linear increases in the transverse momentum transfers with increasing projectile velocities. These observations may be ascribed to diffraction limitations which are connected to electron transfer probabilities P(b) which are significant in limited regions of b only. For the H+ + He single-electron capture we observe two additional maxima in the angular differential cross sections. We conclude that while the secondary maxima at similar to 0.5 mrad probably have large contributions from the Thomas proton-electron-nucleus scattering mechanism, the third maxima at similar to 0.75 mrad are most likely mainly due to projectile de Broglie wave diffraction.
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