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Notes: Present-day Z-pinch experiments generate 200 TW peak power, 5–10 ns duration x-ray bursts that provide new possibilities to advance radiation science. The experiments support both the underlying atomic and plasma physics, as well as inertial confinement fusion and astrophysics applications. A typical configuration consists of a sample located 1–10 cm away from the pinch, where it is heated to 10–100 eV temperatures by the pinch radiation. The spectrally-resolved sample-plasma absorption is measured by aiming x-ray spectrographs through the sample at the pinch. The pinch plasma thus both heats the sample and serves as a backlighter. Opacity measurements with this source are promising because of the large sample size, the relatively long radiation duration, and the possibility to measure opacities at temperatures above 100 eV. Initial opacity experiments are under way with CH-tamped NaBr foil samples. The Na serves as a thermometer and absorption spectra are recorded to determine the opacity of Br with a partially-filled M-shell. The large sample size and brightness of the Z pinch as a backlighter are also exploited in a novel method measuring re-emission from radiation-heated gold plasmas. The method uses a CH-tamped layered foil with Al+MgF2 facing the radiation source. A gold backing layer that covers a portion of the foil absorbs radiation from the source and provides re-emission that further heats the Al+MgF2. The Al and Mg heating is measured using space-resolved Kα absorption spectroscopy and the difference between the two regions enables a determination of the gold re-emission. Measurements are also performed at lower densities where photoionization is expected to dominate over collisions. Absorption spectra have been obtained for both Ne-like Fe and He-like Ne, confirming production of the relevant charge states needed to benchmark atomic kinetics models. Refinement of the methods described here is in progress to address multiple issues for radiation science. © 2002 American Institute of Physics.

Notes: Particle-in-cell simulations of applied-B ion diodes using the QUICKSILVER code [D. B. Seidel et al., in Proceedings of the Europhysics Conference on Computational Physics, Amsterdam, 1990, edited by A. Tenner (World Scientific, Singapore, 1991), p. 475] have been augmented with Monte Carlo calculations of electron–anode interactions (reflection and energy deposition). Extraction diode simulations demonstrate a link between the instability evolution and increased electron loss and anode heating. Simulations of radial and extraction ion diodes show spatial nonuniformity in the predicted electron loss profile leading to hot spots on the anode that rapidly exceed the 350 °C–450 °C range, known to be sufficient for plasma formation on electron-bombarded surfaces. Thermal desorption calculations indicate complete desorption of contaminants with 15–20 kcal/mole binding energies in high-dose regions of the anode during the power pulse. Comparisons of parasitic ion emission simulations and experiment show agreement in some aspects, but also highlight the need for better ion source, plasma, and neutral gas models. © 1999 American Institute of Physics.

Notes: Magnetically insulated ion diodes are being developed to drive inertial confinement fusion. Ion beam microdivergence must be reduced to achieve the very high beam intensities required to achieve this goal. Three-dimensional particle-in-cell simulations [Phys. Rev. Lett. 67, 3094 (1991)] indicate that instability-induced fluctuations can produce significant ion divergence during acceleration. These simulations exhibit a fast growing mode early in time, which has been identified as the diocotron instability. The divergence generated by this mode is modest, due to the relatively high-frequency ((approximately-greater-than)1 GHz). Later, a low-frequency low-phase-velocity instability develops with a frequency that is approximately the reciprocal of the ion transit time. This instability couples effectively to the ions, and can generate unacceptably large ion divergences ((approximately-greater-than)30 mrad). Linear stability theory reveals that this mode has structure parallel to the applied magnetic field and is related to the modified two-stream instability. Measurements of ion density fluctuations and energy-momentum correlations have confirmed that instabilities develop in ion diodes and contribute to the ion divergence. In addition, spectroscopic measurements indicate that lithium ions have a significant transverse temperature very close to the emission surface. Passive thin-film lithium fluoride (LiF) anodes have larger transverse beam temperatures than laser-irradiated active sources. Calculations of the ion beam source divergence for the LiF film due to surface roughness and the possible loss of adhesion and fragmentation of this film are presented. © 1996 American Institute of Physics.

Notes: X-ray powers on the order of 10 TW over an area of 4.5 mm2 are produced in the axial direction from the compression of a low-density foam target centered within a z-pinch on the Z generator.1 The x rays from this source are used for high-energy–density physics experiments, including the heating of hohlraums for inertial confinements fusion studies.2 In this article, detailed characteristics of this radiation source measured using an upgraded axial-radiation-diagnostic suite3 together with other on- and off-axis diagnostics are summarized and discussed in terms of Eulerian and Lagrangian radiation–magnetohydrodynamic code simulations. The source, characterized here, employs a nested array of 10-mm-long tungsten wires, at radii of 20 and 10 mm, having a total masses of 2 and 1 mg, and wire numbers of 240 and 120, respectively. The target is a 14 mg/cc CH2 foam cylinder of 5 mm diameter. The codes take into account the development of the Rayleigh–Taylor instability in the r–z plane, and provide integrated calculations of the implosion together with the x-ray generation. The radiation exiting the imploding target through the 4.5 mm2 aperture is measured primarily by the axial diagnostic suite that now includes diagnostics at an angle of ∼30° to the z axis. The near on-axis diagnostics include: (1) a seven-element filtered silicon-diode array,4 (2) a five-element filtered x-ray diffraction (XRD) array,5 (3) a six-element filtered PCD array,6 (4) a three-element bolometer,7 (5) time-resolved and time-integrating crystal spectrometers, and (6) two fast-framing x-ray pinhole cameras having 11 frames each. The filtered silicon diodes, XRDs, and PCDs are sensitive to 1–200, 140–2300, and 1000–4000 eV x rays, respectively. They (1) establish the magnitude of the prepluse generated during the run in of the imploding wire arrays, (2) measure the Planckian nature of the dominant thermal, and (3) nonthermal component of the emission. The bolometers and XRDs mounted on the near-normal and 30° LOS (line-of-sight) measure the total power and check the Lambertian nature of the emission. Additionally, a suite of filtered fast-framing x-ray pinhole cameras and silicon-diode arrays behind a transmission grating, mounted on LOSs nearly normal to the z axis, quantify the plasma plume exiting the aperture. The hard bremsstrahlung generated is estimated with both on- and off-axis shielded scintillator photomultiplier diagnostics. © 2001 American Institute of Physics.

Notes: Kα emission spectroscopy is an important diagnostic technique used for plasmas created in intense light ion beam experiments.b),c) Emission lines can be produced as 2p electrons drop down to fill 1s vacancies created by the ion beam. Bailey et al.b) reported the first spectroscopic measurements of Kα x-ray satellites in intense proton beam experiments on PBFA-II at Sandia. Kα emission spectra have also recently been observed in intense Li-beam experiments on PBFA-II.d) Two approaches are used to analyze time-integrated x-ray spectra. In the first, CRE calculations are performed to compute synthetic time-integrated spectra using plasma conditions predicted from radiation-hydrodynamic simulations. In the second approach, plasma conditions are deduced from Kα satellite line intensity ratios measured from the highest ionization stages observed in the experiments. Results will be presented from our analysis of recent PBFA-II x-ray spectra. © 1995 American Institute of Physics.

Notes: Stark-shift measurements using emission spectroscopy are a powerful tool for advancing understanding in many plasma physics experiments. We use simultaneous two-dimensional space- and time-resolved spectra to study the electric field evolution in the 20 TW Particle Beam Fusion Accelerator II ion diode acceleration gap. Fiber optic arrays transport light from the gap to remote streaked spectrographs operated in a multiplexed mode that enables recording time-resolved spectra from eight spatial locations on a single instrument. Design optimization and characterization measurements of the multiplexed spectrograph properties include the astigmatism, resolution, dispersion, and sensitivity. A semiautomated line-fitting procedure determines the Stark shift and the related uncertainties. Fields up to 10 MV/cm are measured with an accuracy ±2%–4%. Detailed tests of the procedure confirm that the uncertainty in the wavelength-shift error bars is less than ±20%. Development of an active spectroscopy probe technique that uses laser-induced fluorescence from an injected atomic beam to obtain three-dimensional space- and time-resolved measurements of the electric and magnetic fields is in progress. © 1997 American Institute of Physics.

Notes: A review of the diagnostics used at Sandia National Laboratories to measure the parameters of intense lithium ion-beam hohlraum target experiments on Particle Beam Fusion Accelerator II will be presented. This diagnostic package contains an extensive suite of x-ray spectral and imaging diagnostics that enable measurements of target temperature and x-ray output. The x-ray diagnostics include time-integrated and time-resolved pinhole cameras, energy-resolved one-dimensional streaked imaging diagnostics, time-integrated and time-resolved grazing incidence spectrographs, a transmission grating spectrograph, an elliptical crystal spectrograph, a bolometer array, an 11- element x-ray diode array, and an 11-element PIN diode detector array. The incident Li beam symmetry and an estimate of incident Li beam power density can be measured from ion beam-induced characteristic x-ray line emission and neutron emission. © 1995 American Institute of Physics.

Notes: The test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be α (Alox + Feox), where Alox and Feox are the amounts of aluminium and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil−1, and a value of 0.5 is commonly used for the scaling factor α in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (Pox) so that DPS = Pox/PSC.The relation between PSC and Alox, Feox and Pox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Alox and Feox extracted, but there was also a negative correlation with Pox. When PSC was calculated as the sum of the measured sorption after 252 days and Pox, the multiple regression of PSC on Alox and Feox gave the equation PSC = 36.6 + 0.61 Alox+ 0.31 Feox with a coefficient of determination (R2) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Alox and Feox did not overlap, indicating a significantly larger regression coefficient of P sorption on Alox than on Feox. When loss on ignition was employed as an additional variable in the multiple regression of PSC on Alox and Feox, it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant (P 〈 0.001), the impact of this variable was small as its inclusion in the multiple regression increased R2 by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0–3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water-soluble P than either the Olsen or Morgan tests for P in soil.

Notes: Edge-defined film-fed growth (EFG) Si grown with carbon monoxide (CO) added to the Ar ambient during crystal growth yields solar cells with higher efficiencies than when grown without CO. This increase in cell efficiency is not fully understood. Surface photovoltage, deep-level transient spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to determine the minority carrier diffusion lengths, impurity distributions, and defect structures in uncontaminated, Cr contaminated, and V contaminated EFG material grown with and without CO added to the Ar ambient. We conclude that "SiC-like'' complexes in the near-surface region of the CO ambient material act as gettering sites during crystal growth, and that this gettering action results in lower bulk impurity levels and higher solar cell efficiencies. © 1995 American Institute of Physics.

Notes: A pulsed Na atomic beam source developed for spectroscopic diagnosis of a high-power ion diode is described. The goal is to produce a ∼1012-cm−3-density Na atomic beam that can be injected into the diode acceleration gap to measure electric and magnetic fields from the Stark and Zeeman effects through laser-induced fluorescence or absorption spectroscopy. A ∼10 ns full width at half-maximum (FWHM), 1.06 μm, 0.6 J/cm2 laser incident through a glass slide heats a Na-bearing thin film, creating a plasma that generates a sodium vapor plume. A ∼1 μs FWHM dye laser beam tuned to 5890 Å is used for absorption measurement of the Na I resonant doublet by viewing parallel to the film surface. The dye laser light is coupled through a fiber to a spectrograph with a time-integrated charge-coupled-device camera. A two-dimensional mapping of the Na vapor density is obtained through absorption measurements at different spatial locations. Time-of-flight and Doppler broadening of the absorption with ∼0.1 Å spectral resolution indicate that the Na neutral vapor temperature is about 0.5–2 eV. Laser-induced fluorescence from ∼1×1012 cm−3 Na I 3s-3p lines observed with a streaked spectrograph provides a signal level sufficient for ∼±0.06 Å wavelength shift measurements in a mock-up of an ion diode experiment. © 1997 American Institute of Physics.