# National Institute of Standards and Technology

The most important numerical atomic database at NIST is the Atomic Spectra Database (ASD: http://www.nist.gov/physlab/data/asd.cfm). It contains critically evaluated NIST data for radiative transitions and energy levels in atoms and atomic ions. Data are included for observed transitions of 99 elements and energy levels of 57 elements. ASD contains data on about 950 spectra from about 0.4 Å to 500 μm, with about 77,000 energy levels and 144,000 lines, 60,000 of which have transition probabilities. Following general principles for databasing at NIST only published and evaluated data are included and accuracy must be reported. The data are consistent between spectral lines and atomic levels, which are both in the ASD.

The database is built on MySQL RDBMS and the interface was developed at NIFS using Perl, Java and JavaScript. The interface offers some online derived data in addition to the static data. The database is heavily used; over 400,000 queries were made for spectral lines and over 135,000 for energy levels in the first 11 months of 2009. Compiling new data involves a critical evaluation of the literature, the assessment and possibly change of line identifications, the optimization of energy levels based on multiple sources, the assignment of accuracies, and an internal NIST quality review. A new compilation for Ti is almost finished, a new compilation for Ar is undergoing internal review, and work is in progress on Ba and Sr (many charge states), Ni I and II, and H, He, Li, Be, B, F, Ne and Ar I. Other compilations since 2006/2007 are concerned with Kr, Si, S, Na, Xe and Al (all many charge states) and with Hg I.

There are several bibliographical atomic databases at NIST; concerned with atomic energy levels and spectra, transition probabilities, line broadening, and energy levels and transition probabilities (integrated with ASD). The content has been enriched with direct HTML links to online papers through Digital Object Identifiers. The literature is searched automatically and updates are made on a daily basis. The number of records has grown from 20,000 in 2006 to about 30,000 now.

In addition to the Atomic Spectroscopy Database and the numerical databases the Physics Laboratory at NIST is involved in collisional radiative plasma modeling. The NLTE (non-local thermodynamic equilibrium) series of workshops, most recently NLTE-6 in Dec 2009 in Athens, Greece are organized by NIST and the results of the workshops contribute to the NIST Saha Plasma Kinetics Modeling Database ( http://nlte.nist.gov/NLTE4/ and http://nlte.nist.gov/SAHA/ ), which contains benchmark results for simulation of plasma population kinetics and emission spectra. The on-line NLTE code FLYCHK ( http://nlte.nist.gov/FLYCHK/ ) is available for time-dependent and steady-state calculations of charge state distributions and spectral properties.

- Institution
- National Institute of Standards and Technology, USA
- Contact
- Y. Ralchenko http://nlte.nist.gov/FLY/
- Codes
- MCHF, GRASP2K, FLYCHK, NOMAD
- Description
- MCHF and GRASP2K codes are non-relativistic and relativistic atomic structure packages, respectively, and are used to calculate energy levels, transition probabilities, isotope shifts and hyperfine structure. The FLYCHK code is an on-line CR code (non-Maxwellian plasmas, radiation field, opacity effects and mixtures) available at the above web site, and can produce the following output parameters: reaction rates, ionization distribution, power losses and UTA spectra. FLYCHK contains detailed data for hydrogen-, helium- and lithium-like atoms and ions and uses the hydrogenic approximation with screening parameters for other ions. The NOMAD code is similar to FLYCHK, but is more useful for spectroscopic diagnostics - data normally include detailed structure for all relevant ions, as well as non-Maxwellian ions, radiation field, opacity effects and mixtures. This code is applicable to CXRS problems, and there are plans to have a version on-line in the future.

**Atomic and plasma codes at NIST** ^{[1]}

We present a set of atomic structure and plasma kinetics codes that are being developed or hosted at NIST. The most advanced methods in atomic structure theory are implemented in non-relativistic Multiconfiguration Hartree-Fock (MCHF) and relativistic Multiconfiguration Dirac-Fock (MCDF) codes. An example of an MCDF code is provided by the GRASP2K package which is being maintained and improved by C. Froese Fischer in collaboration with several researchers from other countries. C. Froese Fischer also develops the MCHF code. Both these packages as well as some simpler codes are available for free download from the NIST web site. Yu. Ralchenko presented some examples of recent highly accurate results obtained with MCHF and GRASP2K codes for atoms and ions of relevance to fusion research.

The NIST Atomic Spectroscopy Group also develops sophisticated collisional-radiative models for calculation of plasma population kinetics and emission characteristics. The NOMAD code is used for calculation of spectral patterns in the EBIT experiments with highly-charged ions of tungsten and other heavy elements. This detailed code is also used for simulations on neutral beam spectroscopy in fusion machines, e.g., charge exchange recombination spectroscopy and motional Stark effect. Another advanced collisional-radiative code FLYCHK developed by LLNL researchers and available for online calculations on the NIST site is used by hundreds of researchers, including specialists in fusion plasmas for calculations of ionization distribution, radiative power losses and other important parameters.

**References**