Technical Activities

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"Technical Activities  2005-2007" - Table of Contents

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Atomic Physics Division
The strategy of the Atomic Physics Division is to develop and apply atomic physics research methods, and particulary the interaction between atoms and electromagnetic fields, to achieve fundamental advances in measurement science--some at the quantum limit--relevant to industry and the technical community, and to produce and critically compile physical reference data.


GOAL: To determine
atomic properties and
investigate fundamental
quantum interactions

Strategic Focus Are:

   

First

Light-Matter Interactions and Atom Optics  -  to advance the physics of electromagnetic-matter interactions and to explore new applications for laser cooled and trapped atoms, to study exotic states of matter, and to study and control many-body quantum systems.

Second

Nanoscale and Quantum Metrology  -  to advance measurement science at the atomic and nanometer scale, focusing on ultraprecise length-displacement measurements, x-ray and gamma-ray precision metrology, and nanooptics and nanosystems modeling.

Third

Critically Evaluated Atomic Data  -  to produce reference data on atomic structure, to critically compile reference data for scientific and technological applications, and to develop techniques to apply the data to further the understanding of important plasma devices.

Critically Evaluated Atomic Data:

to produce reference data on atomic structure, to critically compile reference data for scientific and technological applications, and to develop techniques to apply the data to further the understanding of important plasma devices.

INTENDED OUTCOME AND BACKGROUND

The objective of this strategic element is to critically compile fundamental constants and atomic spectroscopy data from the far infrared to the x-ray spectral regions. We disseminate these reference data on the Physics Laboratory website, produce high-quality data for urgent scientific or technological needs,and resolve discrepancies in the body of the data. When reliable data do not exist for high-priority needs, specific measurements or calculations are undertaken to produce them.

The NIST databases for atomic spectra and fundamental constants are recognized throughout the world. We regularly add new material to our flagship database, the Atomic Spectra Database, which now contains data for 141,000 spectral lines and 77,000 energy levels. It experiences over 55,000 requests for data each month. To assist in the diagnostics of a variety of plasmas, we added two new databases that contain benchmark data on plasma population kinetics, i.e., properties of ionized gases. These databases provide researchers with the best available data on numerous plasma parameters, such as mean ion charge state for a plasma under specific conditions. An online computational system for collisional-radiative modeling of hot plasmas under diverse conditions was also added, developed with Lawrence Livermore National Laboratory.

Accomplishments

  • Precision Wavelengths for New Telescopes

    The Very Large Telescope No.1 is one of the largest of a new class of modern telescopes for ground-based astronomy. It is located at the European Southern Observatory in Chile. One of its important missions is to observe spectra of stars and interstellar media at infrared wavelengths, 950 nm to 5500 nm. To do this it uses a major new infrared spectrometer, the Cryogenic High-Resolution Echelle Spectrograph (CRIRES).

    The wavelength scale of this spectrometer is established by spectral lines from a thorium/argon hollow cathode lamp, similar to the platinum/neon lamp used to calibrate spectrometers on the Hubble Space Telescope (HST). Unfortunately, the spectrum of the Th/Ar lamp has not been well studied in the infrared and not enough accurate calibration lines are available.

    To remedy this problem, we made precision measurements of Th/Ar lamps with our 2 m Fourier transform spectrometer. The wavelengths are accurate to about 0.00004 nm. With these new measurements, CRIRES will be able to achieve its astronomical goals.

    In related work for the Hubble Space Telescope, we made observations of Pt/ Ne lamps similar to those to be used to calibrate a new spectrograph to be installed on HST in 2008, the Cosmic Origins Spectrograph (COS). Since the lamps will be used much more intensively on COS than on earlier space spectrographs, there was concern as to whether they would last for the whole mission.

    We performed accelerated aging tests on lamps from the same production run as the COS lamps by running them on an interval timer to simulate their use in space. After each three hundred hours of aging, we used our 10 m vacuum ultraviolet spectrometer to quantitatively measure the spectral output of each lamp. Each lamp was run until it failed (about 1000 h). Although the aging is continuing for some lamps, results to date indicate that the lamps will perform as needed for COS.


    CONTACT: Dr. Gillian Nave
    (301) 975-4311
    gillian.nave@nist.gov



  • Critical Data for Fusion Energy Science: Ionization Energies for Tungsten

    Construction of the International Thermonuclear Experimental Reactor (ITER) will soon start in France. ITER is expected to generate fusion power for periods up to 1000 s. It will be the most expensive science project ever undertaken. An important part of ITER is the divertor, a region of the vessel that exhausts the flow of energy from charged particles and removes helium and other impurities. Tiles of the divertor will be made of tungsten, a material with very high melting point.

    Although the tungsten tiles are able to withstand the high temperatures in ITER, atoms of tungsten will be sputtered into the active gases. To understand the complex processes taking place in these gases, it is important to determine the populations of the various ions of tungsten in the gas. For this it is necessary to have reliable values for the ionization energies of tungsten ions. The ionization energy is the amount of energy required to eject an electron from a given ion so that it is transformed to the next higher ion.

    Previously, only values for the ionization energies of tungsten from rough theoretical calculations were available. We developed a method to determine accurate values for all tungsten ions—from neutral tungsten through almost fully stripped tungsten, W73+. The method is based on scaling results of theoretical calculations according to experimental data. Uncertainties vary from 1.7 % for W2+ to 0.0008 % for W73+, with typical values about 0.1 %. The results are published in Atomic Data and Nuclear Data Tables.


    CONTACT: Dr. Peter J. Mohr
    (301) 975-3217
    peter.mohr@nist.gov



  • Critical Data for Fusion Energy Science: Spectra of Highly Ionized Tungsten

      Figure 9

    Figure 9. Observed spectrum and theoretical modeling of x-ray spectra of tungsten. The labels Cu, ni, and Co refer to the isoelectronic sequences of the stages of ionization of the lines (Cu: W45+; ni: W46+; Co: W47+). The letters 6f, 5f, etc. refer to upper electronic configurations of W46+. The line at 0.79 nm is blend of two transitions forbidden to electric-dipole radiation; one is an electric-quadrupole transition, the other a magnetic-octopole transition.


    In order to help meet the need for spectral data of wall materials in the divertor region of ITER, we excited spectra of tungsten ions with our Electron Beam Ion Trap (EBIT). Spectra in the x-ray region were measured with a microcalorimeter, a new type of spectrometer that detects single photons and measures the rise in temperature to deduce the energy deposited—and hence the wavelength. At longer wavelengths, a grazing-incidence spectrometer was used.

    A number of new spectral lines were identified. The observed spectra were interpreted by means of collisional-radiative modeling of the ionized gas in EBIT. Excellent agreement with the observed spectra was obtained. Fig. 9 shows a spectrum from the microcalorimeter together with a spectrum predicted by modeling calculations.

    According to the calculations, an important strong line at 0.79 nm is actually a blend of two forbidden-type transitions. We showed that electron densities in plasma devices like ITER could be determined by measuring the ratio of the intensities of these two lines. The results are reported in Physical Review A and the Journal of Physics B.


    CONTACT: Dr. Yuri Ralchenko
    (301) 975-3210
    yuri.ralchenko@nist.gov




  • Redefinition of the International System of Units (SI)

    In an effort to improve the International System of Units (SI) to overcome deficiencies, the Fundamental Constants Data Center has published a number of articles describing potential new definitions of the kilogram, ampere, kelvin, and mole, pointing out the merits of these definitions based on prescribed values of the Planck constant, the elementary charge, the Boltzmann constant, and the Avogadro constant.

    The possible new definitions would have advantages including providing a stable, precise, and universal measurement system. With fundamental constant-based definitions of the SI units in place, the values of many of the fundamental physical constants, which are presently determined by experiment and theory, would have exact values, and the uncertainties of many other fundamental constants would be significantly reduced.

    The Fundamental Constants Data Center has worked with relevant organizations to promote the changes in the SI. This includes the Consultative Committee for Units (CCU), the Committee on Data for Science and Technology (CODATA), and the International Union of Pure and Applied Physics (IUPAP).


    CONTACT: Dr. Peter J. Mohr
    (301) 975-3217
    peter.mohr@nist.gov


First strategic focus   |   Second strategic focus   |   Third strategic focus

"Technical Activities  2005-2007" - Table of Contents