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  • 1
    Electronic Resource
    Electronic Resource
    Absolute intensity of a sodium-like resonance line for temperature diagnosis of neon-like X-ray laser plasmas (1990)
    Springer
    Applied physics 50 (1990), S. 193-197 
    Details
    ISSN: 1432-0649
    Keywords: 52.70.La ; 52.25.Nr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Nine different neon-like ions with atomic numbers ranging from 28 to 42 have exhibited gain in various 3p—3s transitions. The temperature of the lasing plasma is critical in determining the state of ionization and the relative importance of collisional excitation and recombination pumping. In this paper we demonstrate a potentially useful new temperature diagnostic for these plasmas that works in the density range of interest for X-ray lasing: the absolute intensity of 3p—3s sodium-like lines. Due to their large collisional couplings and high optical depths, their brightness temperature approaches the actual kinetic temperature of the plasma in temperature and density regimes of importance for achieving optimal X-ray laser performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357283
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  • 2
    Electronic Resource
    Electronic Resource
    An efficient tabulated collisional radiative equilibrium radiation transport model suitable for multidimensional hydrodynamics calculations (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 3480-3489 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A computationally efficient method for transporting radiation in multidimensional plasmas has been developed and evaluated. The basis of this method is a uniform plasma approximation that allows one to utilize existing escape probability techniques that are successfully used in one-dimensional (1D) calculations to approximately solve the multidimensional radiation transport problem. This method is superior to diffusion methods because (1) the probability of escape technique insures that the plasma goes to the correct optically thin and thick limits, (2) the effects of line absorption due to photoexcitations are modeled, and (3) this method uses source functions that are based on a self-consistent nonlocal thermodynamic equilibrium calculation, not an ad hoc assumption that the source functions are Planckian. This method is highly efficient because equation of state information from 1D calculations is tabulated as a function of plasma internal energy, ion density, and the line probability of escape from a uniform plasma, and then used in multidimensional calculations. Given the internal energy and ion density, and by calculating the line probability of escape from a zone of the multidimensional plasma, the equation of state, including emissivities and absorption coefficients, of the zone is determined from the table. Total radiative power, K-shell radiative power, total radiative yield, K-shell radiative yield, and plasma density and temperature profiles obtained from 1D Z-pinch calculations employing this method are in good agreement with the same powers, yields, and profiles calculated using a full radiation transport model. This method has been implemented in the 2D plasma radiating imploding source model code [F. L. Cochran et al., Phys. Plasmas 2, 2765 (1995)] to determine the influence of radiation transport in argon Z-pinch experiments performed on the Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1373415
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  • 3
    Electronic Resource
    Electronic Resource
    XUV spectral observations with two-wavelength laser irradiation (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1837-1839 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: XUV diagnostic equipment was designed and utilized on the OMEGA target chamber at the University of Rochester to study high atomic number plasma generation by two-wavelength laser excitation. Spectral data were collected from silver tracer dot targets irradiated with 1/3 TW of 0.35-μm laser light of the multiple-beam OMEGA laser and the single synchronized 1.06-μm beam of the GDL laser for generating energetic electrons. XUV spectral data in the 30–300-A(ring) region were obtained with both a 3-m grazing incidence spectrograph and a compact 1-m grazing incidence spectrograph designed for reentrant mounting in the OMEGA chamber. High-resolution x-ray spectra were acquired in the 3.6–4.2-A(ring) region with a dual, flat-diffraction crystal spectrograph. A low-resolution x-ray spectrum of silver was recorded with a curved mica spectrograph. Some x-ray spectral lines appeared only when both OMEGA and GDL beams were used. These were identified as 2p–3s,3d transitions in F-like Ag xxxix. F-, Na-, and Mg-like lines were found in the grazing incidence spectra, with F-like lines appearing only with 1.06-μm irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140076
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  • 4
    Electronic Resource
    Electronic Resource
    Analyzing spatially resolved line spectra emitted by Z pinches (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3399-3404 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spatial profiles of key physical variables such as electron temperature and density are crucial in determining the overall radiating efficiency of a Z pinch as well as the emitted photon energy distribution. The present work uses spatially resolved x-ray lines emitted from shots taken on the 4 MA Double EAGLE generator [C. Deeney et al., Phys. Rev. A 44, 6762 (1991)] at Maxwell Physics International to infer such profiles. The loads were arrays of 15 wires consisting of 95% Al, 5% Si, producing nearly 50 kJ of K-shell radiation with relatively long pulsewidths of 41–43 ns. It is found that the spatial profile of the He-like intercombination to resonance line ratio is critically affected by self-absorption and re-emission (scattering) of resonance line photons emitted from the hot, dense interior of the pinch. This ratio cannot be correctly interpreted without taking the scattering into account. Also, at densities somewhat lower than those achieved by these pinches, this line ratio becomes more temperature than density dependent. The inferred temperature gradient is much less steep than that which had been diagnosed previously for a pinch emitting a much shorter x-ray pulsewidth of 13 ns. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874203
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  • 5
    Electronic Resource
    Electronic Resource
    Modeling the coaxial double z-pinch for the Al xi - Mg ix laser at 228 A(ring) (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4303-4309 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A magnetically embedded coaxial z-pinch configuration is proposed for the resonant photoexcitation laser at 228 A(ring) in Mg ix pumped by the 48.338 A(ring) line of Al xi. This laser configuration consists of an annular Al z-pinch plasma imploded (final electron density of about 1020 cm−3) onto an inner, Mg plasma (final electron density of about 1018 cm−3) on the axis. The Mg plasma is confined and stabilized by an axial magnetic Bz field, which is compressed to a final magnitude of about 130 T from an initially applied field of about 1 T by the Al implosion, thus serving to stabilize and physically separate the Al and Mg plasmas. Separate numerical simulations of the Al and Mg plasmas designed to guide exploratory experiments are reported. A 0D dynamic z-pinch model captures the Al implosion, including trapped Bz field and power losses due to line radiation. Initial conditions required to produce the intense Al xi pump line at 48.338 A(ring) are derived assuming an 800 kA, 100 ns implosion current pulse. Assuming a pinch length of 2 cm, a pump power of 3.5 GW/eV is predicted for the 48.338 A(ring) Al xi line. With the pump so defined, a separate, detailed atomic physics model is used to study the photoexcitation kinetics in the Mg ix lasant plasma. It is found that a gain of 1.0–1.5 cm−1 is obtainable on the 2s3d 1D2 - 2s4f 1F3 transition at 228 A(ring) in Mg ix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354394
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  • 6
    Electronic Resource
    Electronic Resource
    Achievable pump power and gain in the Al xi-Mg ix photoresonant x-ray laser (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1957-1961 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The aluminum-magnesium photoresonant x-ray laser scheme is investigated using detailed atomic models for both elements. The aluminum pump source is assumed to be a Z pinch driven by a current of several MA. It is found that monochromatic pump powers of 100 GW/eV are obtainable within the 48-A(ring) aluminum pump line over a broad range (125–400 eV) of pump plasma temperatures. The gain in Mg ix is calculated assuming separations of 1 or 2 cm from the pump plasma. The highest gain appears in the 2s3d 1D2-2s4f 1F3 line at 228 A(ring). However, photoionization as well as resonant photoexcitation appears to be crucial to the success of this scheme. If photoionization by lines other than the pump line is neglected, Mg ix does not exist below∼60 eV. In the 60–100-eV Mg plasma temperature range, collisional excitation from low-lying states to the lower laser level severely degrades the gain. However, when photoionization of Mg by all of the strong Al xi lines is taken into account, Mg ix is found to exist at much lower temperatures, leading to respectable gain of ∼3 cm−1 at 1-cm Al-Mg separation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349479
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  • 7
    Electronic Resource
    Electronic Resource
    Comparison of coolants for achieving short-wavelength recombination lasing (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 33-40 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A promising approach for reducing the operating wavelength of x-ray lasers is the generation of population inversions via recombination in rapidly cooling plasmas. We have examined the relative merits of radiative and hydrodynamic cooling in a freely expanding plasma. The specific lasing scheme studied is recombination in heliumlike silicon, but the general results apply to other elements and ionization stages which are capable of generating gain in the soft x-ray region. We find that the higher radiative cooling rates obtained by mixing the silicon lasant with a high atomic number coolant are more than offset by the reduced expansion cooling brought on by the higher mass density associated with the high-Z elements. Specific results are presented for hydrogen, carbon, aluminum, and selenium coolants mixed with silicon lasant. The present results do not apply to magnetically confined lasant plasmas where high-Z radiators might be valuable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347139
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  • 8
    Electronic Resource
    Electronic Resource
    K-shell radiation physics in the ultrahigh optical depth pinches of the Z generator (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 4476-4483 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Al:Mg alloy wire arrays of mass loads 1.3–3.6 mg/cm have been imploded with peak currents of 19 MA on the 60 TW Z generator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories. The large mass loads have resulted in the highest K-shell x-ray line optical depths (∼103) produced to date in Z-pinches. Analysis of the time-resolved spectrum of a 2.1 mg/cm shot near the time of peak compression has yielded a temperature–density profile of the pinch that approximately reproduces all features of the x-ray data except the continuum above 5 keV, which is underpredicted. The Ly α/He α ratio for Al is shown to be enhanced relative to that of Mg by two mechanisms: photopumped ladder ionization and absorption of the Al He-like line in a cool outer halo. This analysis and comparisons to some Ti shots demonstrates that the K-shell yield of Al is significantly reduced by line and continuum self-absorption, but that of Ti is not. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873185
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  • 9
    Electronic Resource
    Electronic Resource
    Optimization of x-ray emission in Z-pinch implosions: Theory versus experiment (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2590-2596 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three sets of Z-pinch experiments were performed in recent years [Phys. Rev. E 50, 2166 (1994)] that confirmed the existence of a theoretically predicted region in (load mass)-(implosion velocity) space where efficient conversion of implosion energy to kilovolt x rays was possible [J. Appl. Phys. 67, 1725 (1990)]; but they also raised questions about the validity of the theoretical models [Phys. Plasmas 1, 321 (1994)] and about the influence of the pulse-power generator and load design on the detailed behavior of the measured x-ray yields. Newly completed experiments suggest that some of these influences can be overcome and that K-shell yields can be increased in greater accord with theoretical expectations. In this paper, a brief description of these experiments is given, and some comparisons with recent theoretical findings are made along with comparisons with the above-mentioned earlier work. These new comparisons demonstrate the need for further improvements in the theoretical models and in the way experiments are designed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871221
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  • 10
    Electronic Resource
    Electronic Resource
    Evidence for precursor plasma formation resulting from heterogeneous current channels in wire array loads (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1745-1753 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The initial current flow in single and double wire loads exploded by current generators with dI/dt in the range of 1010–1012 A/s has been investigated using laser absorption and interferometric techniques. The results clearly show heterogeneous current channel formation with a plasma corona surrounding a predominantly neutral core. In the two wire load case, the corona is observed to separate from the core and prematurely implode on axis. Parasitic current channels were observed when material, outgassed by a low level prepulse current, is ionized to form a current carrying plasma channel that temporarily shields the wire from the main current pulse. In a complementary study on a terawatt generator, the radiation spectra from Mg coated Al wire array loads contained Mg K-shell lines 10 ns before similar Al lines were observed, confirming the load straggling effects implied by the laser imaging measurements. The results are consistent with theoretical predictions of heterogeneous current channels and precursor plasma formation that lead to a softer implosion, reduced ion density, and reduced x-ray yield. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871693
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