University of Delhi
In recent years, the high quality observational data recorded by space missions such as International Ultraviolet Explorer (EUVE), the Advanced Satellite for Cosmology and Astrophysics (ASCA), the Hopkins Ultraviolet Telescope (HUT), the Hubble Space Telescope (HST), and Solar and Heliospheric Observatory (SOHO), has highlighted the need for highly accurate atomic data. There is no doubt that this situation will be further emphasized by the launch of future space missions such as FUSE. The accuracy of atomic data is crucial for the interpretation of the spectra from these missions in terms of the physical conditions in the astrophysical sources. The need for accurate atomic and molecular data is immense, with applications in such diverse fields such as astronomy, fusion research, and lasers. The type of data depends upon the region or the object being studied. As very few of the ions of interest can be studied experimentally in the laboratory, the user must depend primarily on theoretical data. Nowadays, measurement and calculation of photoionization cross section and collision strength has become a subject of great interest. Photoionization cross sections are necessary for the computation of photoionization and recombination rates for ionization balance in astrophysical plasmas. Accurate electron-impact inner-shell ionization cross section data are necessary for precisely measuring the impurity density in fusion plasma.
In this direction, our group is involved in the calculations of accurate collision strengths, radiative and autoionization decay rates, photoionization cross-sections, oscillator strengths and wavelengths for allowed and forbidden transitions which are needed for the interpretation of observational data and for modeling of astrophysical objects. In our calculations, important physical effects mainly configuration interaction, autoionizing resonances, exchange, coupling and relativistic effects are incorporated by using Configuration Interaction Technique for the atomic structure and accurate R-matrix method for the collisions. For atomic structure calculations, we use grasp2k, GRASP, FAC, CIV3 techniques whereas for collision problems we use very sophisticated R-Matrix (both relativistic and non-relativistic) state of art techniques. We have reported energies and radiative data for E1, E2, M1 and M2 multipole transitions for lowest 110 fine structure levels of the Cs XXV ion. We have identified 46 EUV and 33 SXR spectral lines from ground state. We have predicted many new spectral lines, which are yet to be observed, and which will form the basis for the future experimental work. We have also calculated line intensity ratio (R ) and electron density and studied their behavior graphically with high plasma temperatures.Moreover, for providing support to experimentalists and extend the data base, we reported the atomic data for Ne-like ions (Z = 72-75) by calculating energies and lifetimes for 209 fine structure levels of HfLXIII, Ta LXIV, W LXV and Re LXVI, along with 109 fine structure levels available in the literature for W LXV.Tungsten being a plasma facing material in fusion reactors, EUV and SXR transitions of high Z ions are of Astrophysical interest. Therefore, we have reported the atomic data for W XLIV such as energies for the lowest 100 fine structure levels. Additionally, the radiative data for all E1 and M1 transitions from ground state among the lowest 100 levels were tabulated. We have identified 5 EUV and 38 SXR spectral lines in dipole transitions. We have calculated the line intensity ratio by considering the maximum plasma temperature of 1010 K, which increases with increasing temperature. For T ≥ 109K, the increase in R < 0.001%. This information may be useful for producing optically thin plasma in LTE at higher temperatures for W XLIV.
Professor Man MOHAN
Department of Physics and Astrophysics, Delhi University, Delhi 110007, India