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Adding Ionization and Recombination to CHIANTI

Dr Peter YoungCCLRC/Rutherford Appleton Laboratory, UK

Dr Ken DereGeorge Mason University, USA

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Background

• Tables of ion fractions as a function of temperature are essential for the analysis of electron-ionized plasmas

• In the past, rates have been re-assessed on timescales of ~5 years and new tables published

• Previous calculations include– Mazzotta et al. (1998)– Arnaud & Raymond (1992)– Arnaud & Rothenflug (1985)– Shull & Van Steenberg (1982)

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CHIANTI

• CHIANTI contains atomic data for the calculation of level populations within ions

• Major updates occur every ≈ 2 years

• There is no official CHIANTI ion fraction data-set• The user can choose any of the standard ion fraction tables

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CHIANTI version 6

• v.6 of CHIANTI will provide– ionization rates– recombination rates– ion fractions derived from these rates

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Ionization

• Ionization rates have been assessed, and new calculations performed for many ions– K.P. Dere (2006, submitted to ApJ)

• Experimental cross-section data have been fit with a Burgess & Tully (1992) type fitting formula

• High energy limit given by the Bethe coefficient

f – scaling parameter; I – ionization potential; u = E/I; σ – cross-section

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Fitting the rates

• The ionization rate coefficients are also fit with a Burgess-Tully type scaling

• The spline fits to these scaled rates will be provided to the CHIANTI user

f – scaling parameter; I – ionization potential; t = kT/I; σ – rate coefficient

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Ionization: FAC calculations

• For many ions where experimental data are incomplete or missing, new data have been calculated

• The Flexible Atomic Code (FAC) has been used– relativistic distorted wave code similar to that of Zhang & Sampson

(1991)

Example: Ni XIV

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Radiative Recombination

• The baseline set of radiative recombination rates are derived from fits embedded in a fortran routine of D.A. Verner

• Gives rates for all ions of all elements up to zinc

• These rates are used as the baseline, supplemented by– Badnell (2006)– Wane & Aymar (1987)– Aldrovandi & Pequignot (1974)

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Radiative Recombination Problems

• Beyond the sodium sequence, most of the data have been obtained by interpolation/extrapolation of the Woods et al. (1981) data-set for the iron ions

• Comparisons with other data-sets show differences

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Dielectronic recombination

• Baseline DR rates are taken from Mazzotta et al. (1998)

• New DR rates for all sequences up to the sodium sequence have been calculated by N.R. Badnell and co-workers

• Rates for Cu and Zn were not provided by Mazzotta et al. (1998). These are taken from Mazzitelli & Mattioli (ADNDT, 2002)

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Comparison with Nahar data

• S. Nahar and colleagues have calculated combined RR and DR rates for many ions

• Significant differences exist for some ions for cases where new Badnell data are available, and also where older data are being used

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Blue curve: Badnell data Red curve: Nahar data

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Blue curve: Mazzotta data Red curve: Nahar data

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New CHIANTI ion balance

• Carbon ions

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Conclusions

• Version 6 of CHIANTI should be ready in around 6 months

• For all ions of all elements up to zinc it will contain– ionization rates– recombination rates– ion fraction curves