Engineering topics

Feldman, U.

Publications and source records attributed to Feldman, U..

At least 37 records · Page 2

NASA NTRS1986

Laser-produced spectra and QED effects for Fe-, Co-, Cu-, and Zn-like ions of Au, Pb, Bi, Th, and U

Spectra of very highly charged ions of Au, Pb, Bi, Th, and U have been observed in laser-produced plasmas generated by the OMEGA laser. Line identifications in the region 9-110 A were made for ions in the Fe, Co, Cu, and Zn isoelectronic sequences. Comparison of the measured wavelengths of the Cu-like ions with values calculated with and without QED corrections shows that the inclusion of QED corrections greatly improves the accuracy of the calculated 4s-4p wavelengths. However, significant differences between the observed and calculated values remain.

Seely, J. F.↗

NASA NTRS1986

2s2 2p5-2s2p6 transitions in fluorinelike ions from Zr(31+) to Sn(41+)

Transitions of the type 2s2 2p5-2s2p6 have been observed in eight fluorinelike ions from Zr(31+) to Sn(41+). The spectra were produced by focusing light from the Nd:glass Omega laser at the University of Rochester onto solid targets and photographing the resultant plasmas with a 3-m grazing-incidence spectrograph. The identified transitions are in the region 24-60 A. The measured wavelengths are in good agreement with wavelengths calculated with the semiempirical formulas of Edlen (1983). Wavelengths for the 2s2 2p5 2P3/2-2P1/2 magnetic-dipole transitions are given for each ion.

Reader, Joseph↗

NASA NTRS1986

The extreme-ultraviolet spectrum (300-630 A) of an erupting prominence observed from Skylab

The Skylab 300-630 A images of the January 17, 1974 eruptive spray event imply that the energy input to the arch was maintained during the first 22 min, accompanied by upward motion and heating. From the spectrum obtained, thermal properties are derived for the brightest portion of the nearly straightened leg of the arch. Wavelengths, identifications and intensities are presented for about 90 emission lines formed at temperatures between 100,000 and 1,000,000 K. The emission measure plot obtained is similar to those plots observed for the quiet sun.

Widing, K. G.↗

NASA NTRS1986

Transitions of the type 2s-2p in oxygenlike Y, Zr, and Nb

Transitions of the type 2s-2p in the oxygenlike ions Y XXXII, Zr XXXIII, and Nb XXXIV were identified in spectra recorded at the University of Rochester's Omega laser facility. Solid targets were spherically irradiated by 24 beams of frequency-tripled (351-nm) Nd-glass laser radiation. The spectra were photographed with a 3-m grazing-incidence spectrograph. The identified transitions of the oxygenlike ions are in the range 30 to 73 A. The wavelengths for the magnetic-dipole transitions within the 2s2p4 ground configurations of these ions are predicted from the experimental energy levels.

Behring, W. E.↗

NASA NTRS1986

3s-3p laser gain and X-ray line ratios for the carbon isoelectronic sequence

Calculations have been conducted for the 46 levels belonging to six different configurations in the C I isoatomic sequence, for atomic numbers 18, 22, 26, 30, 34, and 36, with electron densities in the 10 to the 15th to 10 to the 22nd/cu cm range. The 2s2 2p 3p levels' large populations are due to the large electron collisional monopole excitation rates from the ground configuration, as well as to the small radiative decay rates to the ground configuration; this leads to population inversions for transitions of the 3s-3p type. Attention is given to the density-dependence of X-ray line ratios, which represent a promising diagnostic for electron density.

Feldman, U.↗

NASA NTRS1986

Measurement of wavelengths and lamb shifts for inner-shell transitions in Fe XVIII-XXIV

The wavelengths of inner-shell 1s-2p transitions in the ions Fe XVIII-XXIV have been measured in solar flare spectra recorded by the Naval Research Laboratory crystal spectrometer (SOLFLEX) on the Air Force P78-1 spacecraft. The measurements are compared with previous measurements and with recently calculated wavelengths. It is found that the measured wavelengths are systematically larger than the wavelengths calculated using the Z-expansion method by up to 0.65 mA. For the more highly charged ions, these differences can be attributed to the QED contributions to the transition energies that are not included in the Z-expansion calculations.

Seely, J. F.↗

NASA NTRS1986

Spectrum of sodiumlike selenium - Se XXIV

High-resolution spectra of Se XXIV have been obtained with a 3-m grazing-incidence spectrograph. Thin plastic foils coated with selenium were irradiated with four or eight beams of the OMEGA laser in a line-focus configuration. Spectrograms were obtained by viewing the plasma axially. Prominent in the spectra were the 3s-3p and 3p-3d transitions in the 150-240-A region and the transitions nl-(n + 1)l-prime with n = 3, 4 in the 24-80-A region. The energy levels and ionization limit derived from the measured wavelengths are also presented.

Brown, C. M.↗

NASA NTRS1986

Measured wavelengths for n = 4 to 2 transitions in Fe XXIV and Fe XXIII

Accurate wavelength measurements for Fe XXIV and Fe XXIII transitions near 8 A and of the type N = 4 to 2 from solar spectra are presented. The resonance transition in the hydrogenlike ion Mg XII is used as a reference. The measured wavelengths are compared with previous ones and with ab initio and semiempirical calculations that include screening parameters in the nonrelativistic, relativistic, and radiative terms.

Seely, J. F.↗

NASA NTRS1985

High-resolution observations of X-ray transitions in Fe XXV-XXIII

The wavelengths of X-ray transitions in Fe XXV-XXIII have been measured using a high-resolution spectrum reflected from the Ge(13-1) planes. A number of transitions have been resolved for the first time in solar flare spectra, and the contributions of the Fe XXIV n = 3 satellites to the Fe XXV parent lines are discussed. The QED contributions to the wavelengths of the Fe XXIV n = 3 satellite transitions have been determined.

Seely, J. F.↗

NASA NTRS1985

Density sensitive X-ray line ratios in the Be I, B I, and Ne I isoelectronic sequences

The intensities of X-ray transitions in highly charged ions in the Be I, B I, and Ne I isoelectronic sequences have been calculated as functions of electron density. The intensities of the transitions from the 2s(n)2p(m)3p configuration, relative to the intensities from the 2s(n)2p(m)3s and 2s(n)p(m)3d configurations, are strong functions of electron density in high-density plasmas. The density sensitivity occurs at electron densities between 10 to the 16th/cu cm (for Si ions) and 10 to the 22nd/cu cm (for Kr ions). Opacity is unimportant for plasma dimensions that are characteristic of dense laser-produced plasmas. These X-ray line ratios represent a promising new density diagnostic for high-density plasmas.

Feldman, U.↗

NASA NTRS1985

Electron temperature and average density in spherical laser-produced plasmas - Ultraviolet plasma spectroscopy

The average values of the electron temperature Te and the electron density Ne in the corona plasmas of spherically irradiated high-Z targets have been estimated. Targets composed of the elements Cu through Br, Rb, and Mo were irradiated using the fundamental (1.06 microns) and the frequency-tripled (351 nm) output of the Omega laser system. Spectra were recorded in the wavelength region 15-200 A. Using various extreme ultraviolet spectroscopic techniques, it is found that for the case of a Mo plasma produced by frequency-tripled laser irradiation, Te = 2600 + or - 600 eV and Ne is greater than 6 x 10 to the 20th/cu cm. This is consistent with a 'flux limit' smaller than 0.1. The estimated values of Te and Ne are lower in the corona plasmas produced using the fundamental (1.06 micron) irradiation.

Goldsmith, S.↗

NASA NTRS1985

Short wavelength laser calculations for electron pumping in Be I and B I isoelectronic sequences (Z greater than or equal to 18 and less than or equal to 36)

There has been considerable interest in creating large laser gains in the X-ray region from atomic transitions in ne-like ions formed in high-temperature plasmas. Although the Ne-like ions habe received the most attention, it is also possible to produce population inversions in ions of other isoelectronic sequences. Accordingly, it is shown that certain levels of the 2s3p and 2s(2)3p configurations in the Be I and B I isoelectronic sequences can be inverted by collisional pumping relative to levels of the 2s3s and 2s(2)3s configurations. Level populations and gain coefficients were calculated for the most promising transitions, and opacities were calculated for 2s2p-2s3s and 2s(2)2p-2s(2)3s transitions.

Feldman, U.↗

NASA NTRS1985

Transitions of the type 2s-2p in fluorinelike and oxygenlike As, Se, Br, and Rb

Transitions of the type 2s-2p in the F I and O I isoelectronic sequences of arsenic, selenium, bromine, and rubidium have been identified in spectra from laser-produced plasmas. Wavelengths in the range 50 to 90 A were measured to an accuracy of 0.01 A or better. The wavelengths of the magnetic-dipole transitions within the ground configurations are predicted.

Feldman, U.↗

NASA NTRS1985

Characterization of microstrip discontinuities in the time and frequency domains

A number of impedance transitions and interconnections to a microstrip were designed and investigated. The double-step discontinuity on a microstrip was studied in detail, and a procedure was developed to design these structures. Their response was determined by making measurements in both the frequency and time domains in a consistent and repeatable manner. The time-domain presentation of the data was the most useful feature of the measuring system. All undesirable signal components were filtered out through the use of gating functions. Theoretically computed results were verified experimentally.

Feldman, U.↗

NASA NTRS1985

Evidence for gain on the C VI 182 A transition in a radiation-cooled selenium/Formvar plasma

Thin plastic foils coated with selenium have been irradiated using from 4 to 8 beams of the OMEGA laser in a line focus configuration. Spectra were recorded using a 3 meter spectrograph that viewed the plasma along the line focus. Based on a comparison of the intensities of the spectral lines from plasmas with lengths of 1.7, 3.4, 6.8, and 13.6 mm, the C VI n = 3 to 2 transition at 182 A was anomalously intense in the spectra from the longer plasmas. Calculations indicate that the carbon plasma was cooled by radiation from the highly-charged selenium plasma in a time that was smaller than the expansion time of the plasma. These plasma conditions are favorable for the occurrence of population inversions between the n = 2 and 3 levels of C VI resulting from recombination and cascading from higher levels. The measured gain coefficient for the C VI 182 A transition is 3/cm, and this corresponds to a gain-length product of 4 in the longest plasma.

Seely, J. F.↗

NASA NTRS1985

Transitions of the type 2s-2p in highly ionized Cu, Zn, Ga, and Ge

Transitions of the type 2s-2p in the F I, O I, N I, and C I isoelectronic sequences of copper, zinc, gallium, and germanium have been identified in the spectra from plasmas produced by the Omega laser system at the University of Rochester. The wavelengths are in the range 50 to 112 A and are measured using silicon and oxygen lines as wavelength standards for gallium and using several lines from the F I, O I, and Na I isoelectronic sequences as wavelength standards for copper, zinc, and germanium. The energy levels that are determined from the measured wavelengths are also presented. Based on these measurements, the wavelengths for a number of magnetic-dipole transitions within the ground configurations of the F I, O I, and N I isoelectronic sequences are predicted.

Behring, W. E.↗

NASA NTRS1985

High-resolution X-ray spectra of solar flares. VII - A long-duration X-ray flare associated with a coronal mass ejection

It has been recognized that very long duration X-ray events (lasting several hours) are frequently associated with coronal mass ejection. Thus, Sheeley et al. (1983) found that the probability of the occurrence of a coronal mass ejection (CME) increases monotonically with the X-ray event duration time. It is pointed out that the association of long-duration, or long-decay, X-ray events (LDEs) with CMEs was first recognized from analysis of solar images obtained by the X-ray telescopes on Skylab and the Naval Research Laboratory (NRL) slitless spectroheliograph. Recently high-resolution Bragg crystal X-ray spectrometers have been flown on three spacecraft, including the Department of Defense P78-1 spacecraft, the NASA Solar Maximum Mission (SMM), and the Japanese Hinotori spacecraft. In the present paper, P78-1 X-ray spectra of an LDE which had its origin behind the solar west limb on November 14, 1980 is presented. The obtained data make it possible to estimate temperatures of the hottest portion of the magnetic loops in which the emission arises.

Kreplin, R. W.↗

NASA NTRS1985

Population mechanisms for the He(+) n = 3 levels determined from measurements of the solar 1640 A emission

The 1640 A line profile is analyzed using solar data obtained by the NRL slit spectrograph on Skylab. Data from coronal hole regions, quiet sun regions, active regions, prominence regions, and flare regions are presented. The relative densities of 3s, 3p, and 3d levels are determined from the data, and the dominant population mechanisms for these levels are inferred using a rate equation model for the He(+) ion. The relative importance of collisional excitation, radiative recombination, and photoexcitation is determined for each of the solar regions.

Seely, J. F.↗