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Amir Ahmad Saghiri

Amir Ahmad Saghiri
TRIOPTICS GmbH

PhD

About

57
Publications
2,345
Reads
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500
Citations
Additional affiliations
May 1996 - October 1999
Max Planck Institute for Nuclear Physics
Position
  • PostDoc Position
Description
  • Radiative and dielectronic recombination rate measurements of ions at storage ring TSR
March 1994 - March 1996
Universität Heidelberg
Position
  • Research Assistant
Description
  • Neutron diagnostics at experimental fusion Tokamaks TEXTOR and ASDEX by means of nuclear emulsion plates and activation methods.

Publications

Publications (57)
Article
Full-text available
In photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj → nl'j' core excitations (Δn = 0 DR). We have measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe XIX to Fe XVIII Δn = 0 DR. Using our measurements, we have calculated the Fe XVIII and Fe XIX Δn = 0 DR rate coefficients....
Article
Full-text available
We have measured the resonance strengths and energies for dielectronic recombination (DR) of Fe XX forming Fe XIX via N=2 --> N'=2 (Delta_N=0) core excitations. We have also calculated the DR resonance strengths and energies using AUTOSTRUCTURE, HULLAC, MCDF, and R-matrix methods, four different state-of-the-art theoretical techniques. On average t...
Article
Full-text available
We have measured resonance strengths and energies for dielectronic recombination (DR) of Fe XIX forming Fe XVIII via N = 2 → N' = 2 and N = 2 → N' = 3 core excitations. All measurements were carried out using the heavy-ion Test Storage Ring at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We have also calculated these resonan...
Conference Paper
Full-text available
Direct Write Laser lithography (DWL) is an established technology for the creation of microstructures down to lateral dimensions of about 500nm. These systems use a focused laser beam to write structures that are defined by an electronic design directly onto a photoresist coated substrate. In addition to direct writing and the production of phot...
Article
The enhancement of dielectronic recombination of multiply charged ions by external electric fields has been studied under controlled conditions. The heavy ion storage rings CRYRING at Stockholm University and the heavy ion storage ring TSR at the Max-Planck-Institut in Heidelberg were used to store beams of Si11+ (ion energy 280 MeV) and Cl14+ (ion...
Article
In search for interference between radiative and dielectronic recombination (RR and DR) absolute recombination rate coefficients for Ar-like Sc3+ and Ti4+ ions have been measured at the Heidelberg heavy ion storage ring TSR. Whereas the Sc3+ experiment suffers from statistics too poor for a line shape analysis, the Ti4+ recombination spectrum clear...
Article
Radiative and dielectronic recombination of F6+ have been studied at the heavy ion storage ring TSR in Heidelberg. For a detailed investigation of rate enhancement effects at very low electron-ion center-of-mass energies experimental parameters such as the magnetic guiding field, the electron density and the adiabatic expansion factor of the electr...
Article
Full-text available
SU-8 is a negative tone proxy type resist which allows high aspect ratio for micro machining. SU-8 molds can be used for micro casting and embossing for making high aspect MEMS. A quick way to produce prototypes (Design -> Expose -> Prototype) is presently an important task in the micro fabrication. In this work we demonstrate the ability of multip...
Article
Full-text available
We have measured the resonance strengths and energies for dielectronic recombination (DR) of Fe XX forming Fe XIX via N = 2 --> N' = 2 (DeltaN = 0) core excitations. We have also calculated the DR resonance strengths and energies using the AUTOSTRUCTURE, Hebrew University Lawrence Livermore Atomic Code (HULLAC), Multiconfiguration Dirac-Fock (MCDF)...
Article
Full-text available
The low energy C IV dielectronic recombination (DR) rate coefficient associated with 2s-2p Delta n=0 excitations of this lithiumlike ion has been measured with high energy-resolution at the heavy-ion storage-ring TSR of the Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany. The experimental procedure and especially the experimental detecti...
Article
Full-text available
Accurate high temperature dielectronic recombination (DR) rate coefficients are needed to interpret cosmic X-ray spectra. We have shown experimentally that existing DR rates used for plamsa modeling can easily be wrong by factors of 2 or more. These errors affect our ability to derive reliable differential emission measures and chemical abundances...
Article
Full-text available
Dielectronic recombination (DR) of lithium-like Ti19+(1s22s) ions via 2s→2p core excitations has been measured at the Heidelberg heavy ion storage ring TSR. We find that not only external electric fields (0≤E≤280 V cm-1) but also crossed magnetic fields (30 ≤B≤ 80 mT) influence the DR via high-n 2pjnℓ-Rydberg resonances. This result confirms our pr...
Article
Full-text available
Radiative recombination (inverse photoionization) is believed to be well understood since the beginning of quantum mechanics. Still, modern experiments consistently reveal excess recombination rates at very low electron-ion center-of-mass energies. In a detailed study on recombination of F6+ and C6+ ions with magnetically guided electrons we explor...
Article
An introduction to electron–ion recombination processes is given and recent measurements are described as examples, focusing on low collision energies. Discussed in particular are fine-structure-mediated dielectronic recombination of fluorine-like ions, the moderate recombination enhancement by factors of typically 1.5–4 found for most ion species...
Article
Accurate high temperature dielectronic recombination (DR) rate coefficients are needed to interpret solar spectroscopic data. We have shown experimentally that existing DR rates used for plamsa modeling can easily be wrong by factors of 2 or more. These errors affect our ability to derive reliable differential emission measures and chemical abundan...
Article
Full-text available
Dielectronic recombination (DR) of lithium-like Ti [iopmath latex="$^{19+}$"] 19+ [/iopmath] ( [iopmath latex="$\rm1s^2 2s$"] 1s22s [/iopmath] ) ions via [iopmath latex="$\rm 2s\to 2p$"] 2s2p [/iopmath] core excitations has been measured at the Heidelberg heavy ion storage ring TSR. We find that not only external electric fields ( [iopmath latex="$...
Article
Full-text available
Dielectronic recombination has been investigated for Delta-n = 1 resonances of ground-state Li+(1s^2) and for Delta-n = 0 resonances of metastable Li+(1s2s ^3S). The ground-state spectrum shows three prominent transitions between 53 and 64 eV, while the metastable spectrum exhibits many transitions with energies < 3.2 eV. Reasonably good agreement...
Article
Some recent new developments in dielectronic recombination (DR) measurements at heavy-ion storage rings are presented. A DR spectrum measured at CRYRING in Stockholm of F6+ is used to illustrate a few points regarding this kind of measurements. From the spectrum a transversal temperature of the adiabatically expanded electron beam of 3.0(5) meV is...
Article
We report the first experimental observation of magnetic field effects on dielectronic recombination (DR) via highly excited Rydberg levels. Crossed static electric and magnetic fields Ey and Bz were imposed on the collision region in high resolution DR measurements with Li-like Cl14+ ions at the heavy ion storage ring TSR in Heidelberg. Enhancemen...
Article
In a recent theoretical paper Gorczyca et al. [Phys. Rev. A 56, 4742 (1997)] predicted interference between radiative and dielectronic recombination to show up in the total recombination rate coefficient of Ar-like Sc3+(3s23p6) with the signature of interference being an asymmetric line profile of the 3s23p53d22F dielectronic recombination resonanc...
Article
In the search for interference between radiative and dielectronic recombination (RR and DR), absolute recombination rate coefficients for Ar-like ions have been measured at the Heidelberg Test Storage Ring in the centre-of-mass energy range 0-80 eV. The dominant recombination channels beside RR is DR via the formation of (33d ) and (33d ) intermedi...
Article
Recombination of Ar-like Sc3+ ions has been studied experimentally at the TSR for center of mass energies ranging from approximately 12–18 eV. In this energy range rather broad resonances from short lived Sc2+(3s23p53d2 2F) intermediate states are expected. For these resonances recent theoretical work predicts strongly asymmetric lineshapes due to...
Article
New recombination experiments with merged cold beams of electrons and atomic ions have been carried out at the storage ring facilities TSR in Heidelberg, ESR in Darmstadt, and CRYRING in Stockholm. A brief overview is given on the recent activities in which the Giessen group was engaged. Topics of this research were dielectronic recombination (DR)...
Article
The combination of accelerator technology and merged-beams techniques in storage ring experiments has opened up new experimental opportunities for electron-ion collision studies. In particular, charge changing electron-ion interactions at energies reaching from keV down to mueV with meV (and lower) electron beam temperatures have become accessible...
Article
In an X-ray photoionized nebula (XPN) the ionization structure is driven by photoionization balanced by radiative recombination (RR) and DR; and the electron temperature at which an ion is formed is far below the temperature at which the ion would exist in coronal equilibrium. (Kallman et al.), Astrophys. J. 465, 994 (1996). (Arnaud, M. and Raymond...
Article
Full-text available
As an improvement to an earlier study [T. 4742], we have calculated dielectronic recombination rate coefficient spectra for Sc 3+ and Ti 4+ ions as a test case toward the assembly of a data-base [http://homepages.wmich.edu/~gorczyca/drdata/] for the Ar-like isoelectronic sequence required for modeling of dynamic finite-density plasmas [N.R. Badnell...
Article
Full-text available
In photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj ) nl@j@ core excitations (*n \ 0 DR). We have measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe XIX to Fe XVIII *n \ 0 DR. Using our measurements, we have calculated the Fe XVIII and Fe XIX *n \ 0 DR rate coefficients....

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Projects (2)
Archived project
Project
Understand the physics of resonant and non-resonant attachment of an electron to an atomic ion; Explore the influence of external parameters such as electric and magnetic fields as well as their directions on the recombination process and the associated cross sections; Exploit the resonant character of dielectronic recombination in precision spectroscopy of atomic states and measurements of atomic properties including life times of excited states, the charge radius of the nucleus and other parameters that influence hyperfine effects; Provide atomic collision data (mainly cross sections and plasma rate coefficients) for the modeling of astrophysical environments and plasmas in general