摘要:

X-ray spectroscopic measurements of the helium-like and lithium-like argon emission from gas bag targets are presented. These data are supported by Thomson scattering diagnostics providing critical tests of plasma spectroscopic K-shell models. The x-ray spectra show lithium-like dielectronic satellites on the red wing of the He-&bgr; line that are temperature sensitive and are known to influence the shape of the Stark-broadened line profiles observed from implosions. We find that the satellite intensities compare well to kinetics modeling that uses the independently measured electron temperature for satellites whose upper states are populated by dielectronic capture, but discrepancies are observed for inner-shell collisionally excited transitions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361775

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The compressed shell integrity of imploded spherical targets has been studied using the 60-beam, 30-kJ UV OMEGA laser system. The shell integrity is measured by imaging the core emission at different x-ray energies. Time-integrated images of the titanium-doped targets have been obtained using a pinhole array with filters below and above theK-edge energy of titanium and recorded on DEF film. The optical depth ratio between such images reflects the nonuniformity of the cold or absorbing part of the shell. The nonuniformity in emission of pure-CH targets reflects integrity of the hot or emitting part of the shell. Using Fourier transforms of the images, signal modulations have been distinguished from noise. The modulations in shell areal density have been measured to be about 20&percent; to 50&percent; for 20- and 24-&mgr;m shell thicknesses and for square and shaped pulses, with nonuniformities peaked atl∼5of the compressed shell. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361776

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A hard x-ray spectrometer with five channels covering the energy range 1.1–20.1 keV is planned for the study of plasmas produced at the NIF and OMEGA laser facilities. The spectrometer utilizes four crystals in reflection, with a geometry similar to the NOVA HENWAY spectrometer, and one crystal in transmission. Spectra are recorded on CCD detectors with resolving power in the range 315–2800. A related single channel spectrometer, utilizing one transmission crystal and covering 12–60 keV, is presently under construction for the OMEGA laser. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361777

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Significant atomic physics corrections to the measured poloidal velocity using charge exchange spectroscopy have been neglected when interpreting impurity poloidal velocity. In the presence of a magnetic field, the gyro motion of the impurity ion along with the finite lifetime of the observed state results in an additional line shift that scales with ion temperature and magnetic field strength. Effects of collisions on the lifetime of excited states, cascades from higher longer-livednlevels, and charge exchange from excited beam neutrals are calculated to determine necessary corrections to the measured poloidal velocity. The accuracy of computed corrections is tested utilizing symmetric upward and downward views from the TFTR poloidal rotation diagnostic. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361778

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Recent developments concerning the relatively cool and dense divertor region of magnetically confined tokamak fusion plasma devices might play a key role in the realization of useful energy production. Atomic and molecular processes, in turn, critically influence the performance of the divertor. In particular, charge transfer from vibrationally excited hydrogen molecules as well as elastic processes and charge transfer between various ground state hydrogen species (ions, atoms and molecules, in isotopic combinations) could be of critical importance for the momentum transport mechanisms and charge balance in this region. We show here the benchmarking results of our fully quantal calculations for a great number of the relevant processes. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361779

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A brief discussion is presented on some of the methodologies and models that have been employed in modeling radiation production and radiation transport in Z-pinch plasmas. The consequences that stem from the compromises and trade-offs that result from different approximations used for the ionization dynamics and the solution of the transport equations are discussed. We will explore the role radiation plays in the dynamic evolution of a Z-pinch and demonstrate that the radiation cooling can alter pinch dynamics. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361780

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Frequently, the most energetic radiation emitted in abundance from a Z pinch is photons from the H- and He-like stages of the load element(s), i.e., the K shell. Consequently, the K-shell spectroscopy of Z pinches is well established and often used for diagnostics. Four recent advances are described in this paper that have been made in the diagnostic use and interpretation of K-shell radiation emitted from Z pinches. First, use of a trace element in double shell gas puff loads on Double EAGLE (at Maxwell Physics International) has demonstrated that it is the subsequently heated inner puff gas that radiates most of the K-shell photons from the assembled pinch. This finding is consistent with previous data analyses and theory which showed that the hot pinch interior radiates most of the K-shell energy, and shows that little or no mixing of the outer and inner puffs occurs during the implosion and assembly. Second, the use of the intercombination to resonance line ratio to infer density has been reconciled with density determinations based on absolute power. Third, photoexcitations have been shown to substantially alter the interpretation of this line ratio when it is applied to diagnosing the density profile from spatially resolved spectroscopy. Lastly, some wire array experiments using Al:Mg alloy loads at Sandia National Laboratories have specifically demonstrated how more spectral data, properly analyzed, translates into more detailed information about the pinch conditions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361781

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In order to provide benchmark data for models used to interpret X-ray astronomy data from newly-launched orbital telescopes such as Chandra, we have used 120 TW, 180 eV pinch plasmas on the Sandia Z facility to drive iron foils into X-ray photoionized equilibrium. The experiment was designed to achieve photoionization parameters characteristic of accretion-powered objects such as X-ray binaries (neutron stars) and active galactic nuclei (black holes). These objects comprise roughly half of observed X-ray sources, but the interpretation of their spectra is difficult: state-of-the-art models for photoionized iron plasmas do not yet agree on the expected ionization balance. In our initial experiments the foil samples consisted of 200 Å of iron codeposited with 300 Å of sodium fluoride and sandwiched between two 1000 Å layers of Lexan (CH and O). We characterized the pinch spectrum, temperature, power and uniformity and qualified it as a photoionization driver. We obtained time-integrated absorption spectra for the foil from 8 to 18 Å and identified spectral lines from O VIII, F IX, Na X and XI, and Fe XVII and XVIII, i.e. neon-line and fluorine-like iron. Time-resolved absorption and emission spectra for the foils were also obtained from 12.5 to 16 Å, and hydrogen-like F and neon-like and fluorine-like Fe were again observed in the 2 ns time window of interest. In subsequent ridealong experiments we have developed a density diagnostic and measured the density via foil-expansion imaging at two locations. We conclude by discussing upcoming experiments at Z in which we plan to obtain a full data set of plasma density, temperature, and absorption and emission spectra for multiple photoionization equilibria. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361782

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The X-ray sources in the 4–7 keV energy regime can be produced by laser-irradiating high-Z gas-filled targets with high-powered lasers. A series of experiments have been performed using underdense targets that are supersonically heated with ∼35 kJ of 0.35 &mgr;m laser light. These targets were cylindrical Be enclosures that were filled with 1–2 atms of Xe gas. L-shell x-ray emission is emitted from the plasma and detected by Bragg crystal spectrometers and x-ray diodes. Absolute flux measurements show conversion efficiencies of ∼10&percent; in the multi-kilovolt x-ray emission. These sources can be used as bright x-ray backlighters or for material testing. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361783

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

New X-ray laser schemes exploiting the fast (<10 femtosecond) decay of specific inner-shell hole states via Coster-Kronig and super Coster-Kronig decay processes are analyzed. Computer simulation for Ca and Ti shows, that population inversion can be achieved by electron collisional ionization only, and also by using fast, incoherent X-ray pumping. Macroscopically observable gain requires extremely fast energy deposition: laser produced plasma on solid density target surfaces, excited by <25 fs, Joule level optical energy. Experiments performed with the >1 J energy, compressed pulses of a chirped pulse amplification Ti:sapphire laser system, and with specially designed multilayer metal targets containing high Z (Au) radiator and low Z (Ti) emitter show anomalous spectral line enhancement in the 2–14 nm wavelength range. Threshold conditions for gain by incoherent X-ray pumping, conversion efficiency of visible laser photons into a desired X-ray bandwidth, and the design considerations of the multilayer target structure are also discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361784

出版商:AIP    

年代:1900

数据来源: AIP