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We present a broad study of linear, clustered, noble gas puffs irradiated with the frequency doubled (527 nm) Titan laser at Lawrence Livermore National Laboratory. Pure Ar, Kr, and Xe clustered gas puffs, as well as two mixed-gas puffs consisting of KrAr and XeKrAr gases, make up the targets. Characterization experiments to determine gas-puff density show that varying the experimental parameter gas-delay timing (the delay between gas puff initialization and laser-gas-puff interaction) provides a simple control over the gas-puff density. X-ray emission (>1.4 keV) is studied as a function of gas composition, density, and delay timing. Xe gas puffs produce the strongest peak radiation in the several keV spectral region. The emitted radiation was found to be anisotropic, with smaller X-ray flux observed in the direction perpendicular to both laser beam propagation and polarization directions. The degree of anisotropy is independent of gas target type but increases with photon energy. X-ray spectroscopic measurements estimate plasma parameters and highlight their difference with previous studies. Electron beams with energy in excess of 72 keV are present in the noble gas-puff plasmas and results indicate that Ar plays a key role in their production. A drastic increase in harder X-ray emissions (X-ray flash effect) and multi-MeV electron-beam generation from Xe gas-puff plasma occurred when the laser beam was focused on the front edge of the linear gas puff.

Beam combination via an ion wave plasma optic is discussed, including measurement of the power transfer (pump depletion and seed amplification) for several seed pulse durations and total pump energies, with accompanying simulation studies.

In a hot, under-dense plasma, eight input beams are combined into a single, well-collimated beam, whose energy is more than triple than that of any incident beam. This shows how nonlinear interactions in plasmas can produce optics beams at much higher intensity than possible in solids.

We have studied the titanium K-shell emission spectra from multi-keV x-ray source experiments with hybrid targets on the OMEGA laser facility. Using the collisional-radiative TRANSPEC code, dedicated to K-shell spectroscopy, we reproduced the main features of the detailed spectra measured with the time-resolved MSPEC spectrometer. We have developed a general method to infer the Ne, Te and Ti characteristics of the target plasma from the spectral analysis (ratio of integrated Lyman-α to Helium-α in-band emission and the peak amplitude of individual line ratios) of the multi-keV x-ray emission. These thermodynamic conditions are compared to those calculated independently by the radiation-hydrodynamics transport code FCI2.

The energetics of novel silver halfraum targets are presented from laser experiments at the National Ignition Facility (NIF). Four beams from the NIF laser were used to heat the halfraum targets with ∼10 kJ of energy in a 1 ns square laser pulse. The silver halfraum targets were spheres 2 mm in diameter with an 800 μm laser entrance hole (LEH). Targets with different spherical wall thicknesses (8–16 μm) were characterized. The energetics and the laser coupling to the targets were determined using the NIF X-ray (i.e. Dante and FFLEX spectrometers) and optical backscatter diagnostics (NBI and FABS). The energy coupled into the targets was 0.85–0.88 of the total laser energy with a defocused laser spot of 400 μm in diameter and no spatial smoothing of the beams with phase plates. The coupling increased to 0.92 when 400 μm spot size phase plates were used to smooth each of the four lasers beams. The energy losses from the targets were through X-ray radiation and backscatter from laser plasma instabilities (SBS and SRS) from the LEH. As expected the different wall thickness had different levels of burn through emission. The thickest walled target (∼15.9 μm) had very low radiative losses through the target wall. The thinnest walled targets (∼8 μm) radiated about 0.2 of the input energy into X-ray emission.

A scaled experiment comprising a laser-driven explosion in a cavity is used to characterize the coupling of mechanical energy into the surrounding solid material. Experiments are performed using poly(methyl methacrylate) and dry Salem limestone as the explosion containment blocks materials, in which are milled scaled spherical cavities of various dimensions. Measurements of the coupled shock, taken with fiber optic probes at the cavity wall, show the critical radius where wall deformation transitions from plastic to elastic deformation. These measurements also provide a diagnostic of the air blast, which is validated against GEODYN simulation code. The measurement of the coupled shock amplitude taken farther from the wall in the linear region indicates increased coupling efficiency in small cavities over the range of scaled cavity radii from 6 to 20 m / kt 1 / 3, a phenomenon not previously observed in experiments. A comparison of results taken in this experiment with a parallel experiment using high explosive (HE) as the source shows that coupled shocks generated with HE are characteristically different with much larger amplitude than those produced by a high energy density laser-driven source with the same yield. This experimental technique potentially provides a rapid and cost-effective method to analyze the consequences of a full-scale, low yield, buried explosion.A scaled experiment comprising a laser-driven explosion in a cavity is used to characterize the coupling of mechanical energy into the surrounding solid material. Experiments are performed using poly(methyl methacrylate) and dry Salem limestone as the explosion containment blocks materials, in which are milled scaled spherical cavities of various dimensions. Measurements of the coupled shock, taken with fiber optic probes at the cavity wall, show the critical radius where wall deformation transitions from plastic to elastic deformation. These measurements also provide a diagnostic of the air blast, which is validated against GEODYN simulation code. The measurement of the coupled shock amplitude taken farther from the wall in the linear region indicates increased coupling efficiency in small cavities over the range of scaled cavity radii from 6 to 20 m / kt 1 / 3, a phenomenon not previously observed in experiments. A comparison of results taken in this experiment with a parallel experiment using hig...

A novel concept for using hybrid targets to create multi-keV X-ray sources was tested on the GEKKO XII facility of the OSAKA University and on the OMEGA facility of the University of Rochester. The sources were made via laser irradiation of a titanium foil placed at the end of a plastic cylinder, filled with a very low-density (2 and 5 mg/cm3) silicon-dioxide aerogel that was designed to control the longitudinal expansion of the titanium plasma. Preliminary calculations were used to determine optimal conditions for the aerogel density, cylinder diameter and length that maximize multi-keV X-ray emission. The X-ray emission power was measured on OMEGA using absolutely calibrated broad-band, diode-based CEA diagnostics, in addition to high resolution crystal spectrometers. On GEKKO XII, the heat wave propagation velocity in the aerogel was also measured with an X-ray framing camera. The advantage of using the thermal wave generated in the aerogel to heat a solid material to increase the conversion efficiency has not been fully demonstrated in these experiments. However, it was shown that a 5 mg/cm3 aerogel placed in front of a titanium foil can improve the x-ray conversion efficiency with respect to the case of 2 mg/cm3 for some target diameter and length.

K-shell X-ray emission from laser-irradiated planar Zn, Ge, Br, and Zr foils was measured at the National Ignition Facility for laser irradiances in the range of 0.6–9.5 × 10 15 W/cm 2 . The incident laser power had a pre-pulse to enhance the laser-to-X-ray conversion efficiency (CE) of a 2–5 ns constant-intensity pulse used as the main laser drive. The measured CE into the 8–16 keV energy band ranged from 0.43% to 2%, while the measured CE into the He-like resonance 1 s 2–1 s 2 p (1P) and intercombination 1 s 2–1 s 2 p (3P) transitions, as well as from their 1 s 2(2 s ,2 p ) l –1 s 2 p (2 s ,2 p ) l satellite transitions for l = 1, 2, 3, corresponding to the Li-, Be-, and B-like resonances, respectively, ranged from 0.3% to 1.5%. Absolute and relative CE measurements are consistent with X-ray energy scaling of ( hν ) −3 to ( hν ) −5 , where hν is the X-ray energy. The temporal evolution of the broadband X-ray power was similar to the main laser drive for ablation plasmas having a critical density surface.

Current inertial confinement fusion experiments on the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)] are attempting to demonstrate thermonuclear ignition using x-ray drive by imploding spherical targets containing hydrogen-isotope fuel in the form of a thin cryogenic layer surrounding a central volume of fuel vapor [J. Lindl, Phys. Plasmas 2, 3933 (1995)]. The fuel is contained within a plastic ablator layer with small concentrations of one or more mid-Z elements, e.g., Ge or Cu. The capsule implodes, driven by intense x-ray emission from the inner surface of a hohlraum enclosure irradiated by the NIF laser, and fusion reactions occur in the central hot spot near the time of peak compression. Ignition will occur if the hot spot within the compressed fuel layer attains a high-enough areal density to retain enough of the reaction product energy to reach nuclear reaction temperatures within the inertial hydrodynamic disassembly time of the fuel mass ...

Our team has developed an experimental platform to evaluate the x-ray-generated stress and impulse in materials. Experimental activities include x-ray source development, design of the sample mounting hardware and sensors interfaced to the National Ignition Facility’s diagnostics insertion system, and system integration into the facility. This paper focuses on the X-ray Transport and Radiation Response Assessment (XTRRA) test cassettes built for these experiments. The test cassette is designed to position six samples at three predetermined distances from the source, each known to within ±1% accuracy. Built-in calorimeters give in situ measurements of the x-ray environment along the sample lines of sight. The measured accuracy of sample responses as well as planned modifications to the XTRRA cassette is discussed.

Spectrally and time-resolved x-ray scattering is used to extract the temperature and charge state evolution in a near solid density carbon foam driven by a supersonic soft x-ray heat wave. The measurements show a rapid heating of the foam material ($\ensuremath{\sim}200\text{ }\text{ }\mathrm{eV}/\mathrm{ns}$) followed by a similarly fast decline in the electron temperature as the foam cools. The results are compared to an analytic power balance model and to results from radiation-hydrodynamics simulations. Finally, the combination of charge state and temperature extracted from this known density isochorically heated plasma is used to distinguish between dense plasma ionization balance models.

The nanostructure of very-low-density aerogels (< 10 mg/cm3) affects the laser heating and propagation of the subsequent heat front. Simulations treat these materials as an atomistic medium without any structure differentiating between near-solid-density material and voids. Thus, simulations fail to predict the effects of the aerogel’s physical micro or nanostructure on the laser-matter interaction. We have designed an experiment using the GEKKO XII laser and ILE diagnostics to characterize the ionization-wave propagation and x-ray yield from aerogel and mass-matched gaseous targets as the laser passes through each. By design, the gas and aerogel targets will have identical densities and identical effective ionization states.

The sensitivity of Fuji SR and MS image plates (IPs) used in x-ray spectrometers on OMEGA and the National Ignition Facility has been measured using two techniques. A set of radioisotopes has been used to constrain image-plate sensitivity between 6 and 60 keV, while a Manson source has been used to expose image plates to x rays at energies between 1.5 and 8 keV. These data have shown variation in sensitivity on the order of 5% for a given IP type and scanner settings. The radioisotope technique has also been used to assess IP fading properties for MS-type plates over long times. IP sensitivity as a function of scanner settings and pixel size has been systematically examined, showing variations of up to a factor of 2 depending on the IP type. Cross-calibration of IP scanners at different facilities is necessary to produce a consistent absolute sensitivity curve spanning the energy range of 2-60 keV.

Combining laser beams in a plasma is enabled by seeded stimulated Brillouin scattering which allows cross-beam energy transfer (CBET) to occur and re-distributes the energy between beams that cross with different incident angles and small differences in wavelength [Kirkwood et al. Phys. Plasmas 4, 1800 (1997)]. Indirect-drive implosions at the National Ignition Facility (NIF) [Haynam et al. Appl. Opt. 46, 3276–3303 (2007)] have controlled drive symmetry by using plasma amplifiers to transfer energy between beams [Kirkwood et al., Plasma Phys. Controlled Fusion 55, 103001 (2013); Lindl et al., Phys. Plasmas 21, 020501 (2014); and Hurricane et al. Nature 506, 343–348 (2014)]. In this work, we show that the existing models are well enough validated by experiments to allow a design of a plasma beam combiner that, once optimized, is expected to produce a pulse of light in a single beam with the energy greatly enhanced over existing sources. The scheme combines up to 61 NIF beams with 120 kJ of available energy...

This work was motivated by previous findings that the measured laser-driven heat front propagation velocity in under-dense TiO2/SiO2 foams is slower than the simulated one [Perez et al., Phys. Plasmas 21, 023102 (2014)]. In attempting to test the hypothesis that these differences result from effects of the foam microstructure, we designed and conducted an experiment on the GEKKO laser using an x-ray streak camera to compare the heat front propagation velocity in “equivalent” gas and foam targets, that is, targets that have the same initial density, atomic weight, and average ionization state. We first discuss the design and the results of this comparison experiment. To supplement the x-ray streak camera data, we designed and conducted an experiment on the Trident laser using a new high-resolution, time-integrated, spatially resolved crystal spectrometer to image the Ti K-shell spectrum along the laser-propagation axis in an under-dense TiO2/SiO2 foam cylinder. We discuss the details of the design of this ...

Charge state distributions (CSDs) have been determined in low-density (≈1012 cm–3) gold plasmas having either a monoenergetic beam (EBeam = 2.66, 3.53, 4.54, 5.35, 5.85, and 6.35 keV) or experimentally simulated thermal electron distributions (Te = 2.0, 2.5, and 3.0 keV). These plasmas were created in the Livermore electron beam ion traps, EBIT-I and EBIT-II. Line emission and radiative recombination features of K to Kr-like gold ions were recorded in the X-ray region with a crystal spectrometer and a photometrically calibrated microcalorimeter. The CSDs in the experimentally simulated thermal plasmas were inferred by fitting the observed 4f → 3d and 5f → 3d lines with synthetic spectra from the Hebrew University Lawrence Livermore Atomic Code (HULLAC). Additionally, the CSDs in the beam plasmas were inferred both from fitting the line emission and fitting the radiative recombination emission to calculations from the General Relativistic Atomic Structure Program. Despite the relatively simple atomic physics in the low-density plasma, differences existed between the experimental CSDs and the simulations from several available codes (for example, RIGEL). Our experimental CSD relied upon accurate electron impact cross sections provided by HULLAC. To determine their reliability, we have experimentally determined the cross sections for several of the n = 3 → 4 and n = 3 → 5 excitations in Ni to Ga-like Au and compared them to distorted wave calculations. Cross-section calculations by flexible atomic code (FAC) and HULLAC were found to be very consistent. Recent Au spectra recorded during experiments at the OMEGA laser facility are presented and compared with those recorded from EBIT-I and EBIT-II. This comparison shows that spectra from the two sources are surprisingly similar despite a 10 order of magnitude difference in their respective plasma densities. PACS Nos.: 52.50.Fs, 52.25.Jm, 34.80.Kw, 34.80.Lx

Data produced by an electron beam ion trap (EBIT) can be crucial for interpreting spectra from plasmas created by long-pulse lasers. Four example spectra are considered: (i) the spectra from the hot gold plasma in the laser deposition region of a hot hohlraum, (ii) the He-β spectra from an argon-doped imploding core of an inertial confinement fusion capsule, (iii) the polarization in spectral lines produced by hot electrons generated by laser-plasma parametric instabilities, and (iv) the spectra of the underdense plasma from an aerogel X-ray source. The EBIT data needed for these cases are: (i) the line positions for 3 → 2 transitions in open M shell gold ions, (ii) the Li-like satellite lines for the K-β transition in open L shell argon ions, (iii) the polarization of suitable X-ray lines at 30 keV, and (iv) the precise wavelengths of K lines of highly charged Si ions and the precise wavelengths of L and K lines of highly charged Ge ions.PACS Nos.: 52.25.Os, 52.38.–4, 52.38.Bv, 52.57.–z, 52.57.Fg, 52.59.Px, 52.70.–m 52.70.La

Atomic data for electron impact ionization of all the elements from H to Ge are reviewed, the rates for these processes needing to be regularly updated following the publication of new experimental data and new theoretical calculations. Experimental cross sections, along with specific theoretical calculations when experimental data are missing, are fitted as functions of the electron energy, and from these fits ionization rate coefficients can be evaluated. It has been possible to take into account all elements but not all charge states of every element. Since the purpose of the paper is to update the ionization data evaluated and proposed in previous review papers, it is discussed if modifications are needed for the ions not considered. For highly ionized ions starting from the Ne- like iso- electronic sequence corrections do not appear necessary. On the other hand, except for Fe, for slightly ionized ions, specifically below the S- like iso- electronic sequence, the previously proposed data often underestimate the total ionization cross section, since only direct ionization channels have been considered and indirect processes have been neglected. Multiplicative correction coefficients are given to agree with recently published theoretical calculations. Experimental ionization data are considered, even when the presence of populated metastable levels ( related to the electron density inside the source) is reported in the ion beams involved in the cross- section data measurements. We deem such a procedure acceptable when the proposed rates have to be included in codes that simulate the impurity behaviour in magnetic- confinement fusion devices, i. e., when radial transport is added to ionization and recombination to predict spatially resolved charge- state distributions. On the other hand, for astrophysical plasmas the contributions of metastable levels to the experimental data may represent a serious problem since, generally, the values of the electron densities that are involved are much lower than those in the ion sources. However, we critically investigated this problem and we found that the presence of metastables does not significantly modify the rates of most of the ions apart from a dozen. For this set of ions we provide different, corrected rates. Recombination is not considered since a review has been recently published.

Atomic data for both ionization and recombination of Kr and Mo ions are reviewed, the rates for these processes needing to be regularly updated following the publication of new theoretical calculations and new experimental data. Kr is used in magnetic-confinement fusion devices to produce a peripheral radiating mantle meant to spread the heat load on the plasma-facing components. In a few tokamaks Mo tiles cover the plasma-facing surfaces, acting in most cases as a plasma-column limiter. The collected atomic data represent the state of the art on the ionization and recombination data for the two considered elements. Samples of rates are proposed for both ionization and recombination along with tables of the fractional abundances at ionization equilibrium. The proposed rates should be included in codes that simulate the impurity behaviour in magnetic-confinement fusion devices, i.e., when radial transport is added to ionization and recombination to predict spatially resolved charge-state distributions to be compared with experimental results. As an example, the simulation of a Mo laser blow-off injection on the JET tokamak is re-analysed with the revised rates and multiplicative correction factors are obtained for the rate ratios recombination over ionization for L-shell ions.

Laser-Produced plasmas at subcritical densities have proven to be efficient sources for X-ray production. In this context, we obtain experimental results from Kr and Xe gas-filled targets that were irradiated by the OMEGA (Laboratory for Laser Energetics, University of Rochester) laser. Nearly 40% of the laser energy was converted into X-rays in the L-shell-photon-energy range (≥ 1.6 keV) by a Kr-filled target. The conversion efficiency measurements were correlated with time-resolved plasma-temperature measurements done by means of a Thomson-scattering diagnostic. The measured range of temperatures, between 2-3.5 keV, is in good agreement with LASNEX radiation-hydrodynamics simulations. X-ray-cooling rates and charge-state distributions were computed using detailed atomic data from the HULLAC suite of codes. X-ray yields predicted by the cooling-rate calculations are compared to measured spectra, and good agreement is found for predictions made with highly-detailed atomic models. We find that X-ray conversion efficiency in Kr-filled targets is a strong function of temperature, and has an optimum density near 15% of the laser's critical density. © 2005 Elsevier Ltd. All rights reserved.

The superconfiguration (SC) approach to collisional-radiative modeling can significantly decrease the computational demands of finding non-LTE level populations in complex systems. However, it has not yet been fully determined whether the statistical averaging of SC models leads to a significant loss of accuracy. The present work compares results from two independent models: a detailed-level accounting (DLA) model based on HULLAC data and the SC model MOST. The relatively simple level structures of the K- and L-shell ions of the neon test system ensure a tractable number of levels for the DLA model but challenge the statistical assumptions of the SC approach. Nonetheless, we find fair agreement between the two models for average ion charges, SC populations, and various effective temperatures.

The charge state distributions of Fe, Na and F are determined in a photoionized laboratory plasma using high-resolution X-ray spectroscopy. Independent measurements of the density and radiation flux indicate the ionization parameter ξ in the plasma reaches values ξ = 20 – 25 erg cm s - 1 under near steady-state conditions. A curve-of-growth analysis, which includes the effects of velocity gradients in a one-dimensional expanding plasma, fits the observed line opacities. Absorption lines are tabulated in the wavelength region 8– 17 A . Initial comparisons with a number of astrophysical X-ray photoionization models show reasonable agreement.

Systematic variation of the electron-beam energy in an electron-beam ion trap has been employed to produce soft-X-ray spectra of Os, Bi, Th, and U with the highest charge states ranging up to Ni-like ions. Guided by relativistic atomic structure calculations, the strongest lines have been identified with Δn = 0 (n = 4 to n′ = 4) transitions in Rb- to Cu-like ions. The rather weak 4p–4d transitions are much less affected by QED contributions than the dominant 4s–4p transitions. Our wavelength measurements consequently provide benchmarks with and (almost) without QED. Because the radiative corrections are not very sensitive to the number of electrons in the valence shell, our data, moreover, provide benchmarks for the evaluation of electron–electron interactions. PACS Nos.: 32.30.Rj, 39.30.+w, 31.50.+w

We are measuring the cross sections for the 3d → 4f and 3d → 5f excitations in Ni- to Ga-like Au in beam plasmas created in the Livermore electron beam ion trap EBIT-I. The measurements are possible by using the high-resolution broadband coverage of the Goddard Space Flight Center micro-calorimeter. The cross sections are determined from the ratio of the intensity of the collisionally excited lines to the intensity of the radiative recombination lines. The value of the excitation cross section of the 3d 3/2 → 5f 5/2 transition in Au 50+ (Cu-like) is presented and compared to distorted wave calculations.

A series of underdense laser plasma interaction experiments performed on the Helen laser [M. J. Norman et al., Appl. Opt. 41, 3497 (2002)] at the Atomic Weapons Establishment (AWE), U.K., using 2ω light have uncovered a strong dependence of laser backscatter and hot electron production on plasma composition. Using low-Z materials, we find a behavior familiar from previous 3ω work, the interchange of stimulated Raman scattering for Brillouin scattering as we change from gases that have high ion wave damping (e.g., C5H12) to gases with low ion wave damping (e.g., CO2). However, as Z is increased, we find that Brillouin scattering drops while Raman scattering remains low. For gases with Z greater than 18, it is possible to have long scalelength, underdense plasmas with both low Brillouin and Raman backscatter losses. Complementary measurements of hot electron production show efficient production of hot electrons in C5H12 plasmas approaching 0.25ncr, but changing the plasma composition can greatly suppress th...

The method of superconfiguration (SC) temperatures is used for interpreting the experimental spectrum of a non-LTE xenon plasma with kT e =450 eV and n e =1.2×10 20 cm −3 . 109 SCs are selected for representing the eight relevant ions. The coefficients of the linear equations for the populations and the temperatures of these SCs are deduced from the rates of the atomic processes between the constituent configurations. The obtained ion balance is close to the results of previous calculations by other methods. The simulated spectrum agrees very well with the experimental spectrum.

We measure the He-like, time-resolved emission from two types of thin foils (1) consisting of 250 A of carbon together with 250 A of aluminum and (2) 500 A aluminum, illuminated with a 150 fs laser pulse at an intensity of 10 19 W / cm 2 . Dielectronic satellite contributions to the resonance transitions 1s 2 – 1 s 2 p ( 1 P ) , 1s 2 – 1 s 3 p ( 1 P ) , and 1s 2 – 1 s 4 p ( 1 P ) are modeled using the configuration-averaged code AVERROES and is found to be significant for all three resonance lines. The effects of opacity are inferred from the data and found to be significant only in the 1s 2 – 1 s 2 p ( 1 P ) .

The construction of the Tesla Test Facility at DESY, a short pulse tunable soft X-ray free electron laser (FEL) source based on the self-amplified spontaneous emission (SASE) process, will provide a major advance in the capability for dense plasma-related and warm dense matter research. This source will provide 1013 photons in a 200 fs duration pulse that is tunable from ∼6 to 100 nm . Laser-based plasma spectroscopic techniques have been used with great success to determine the line shapes of atomic transitions in plasmas, study the population kinetics of atomic systems embedded in plasmas, and look at the redistribution of radiation. However, the possibilities for optical lasers end for plasmas with n e ⩾10 22 cm −3 as light propagation is severely altered by the plasma. Since an XUV-FEL will not have this limitation the entire field of high density plasma kinetics in laser produced plasma will then be available to study with the tunable source. Thus, one will be able to use these X-ray sources to pump individual transitions creating enhanced population in the excited states that can be easily monitored. We show two case studies illuminating different aspects of plasma spectroscopy.

We review the first “virtual workshop” designed to compare NLTE emissivities produced by widely differing types of atomic physics codes. A small set of significant results, illustrating the progress that is still to be achieved, is presented. We conclude with some lessons learned and possible avenues for future progress.

We present observations of high-n transitions in the spectra of neon-like Cu19+ and Zn20+ ions observed in a variety of laser-produced plasmas (LPPs). The spectra are recorded with spectral resolution λ/Δλ=3000–8000 from three different laser sources: a 15 ns -pulse length Nd:glass, a ps-pulse length Nd:glass, a 12 ns -pulse length XeCl laser. These spectral observations are used to classify the transitions in the 2p–nd and 2s–np Rydberg series of the Ne-like copper and zinc ions, and to derive their first and second ionization energies. The plasma X-ray emission is simulated with a steady-state collisional-radiative model that includes the effect of self-absorption on line intensities, and the effect of hot-electron populations on the ionization balance. These spectra, along with those in our other recent work, provide a comprehensive set of data that can be used to test the accuracy of atomic-structure calculations, and to demonstrate the importance of opacity and hot electron effects on high-n transitions.

We have observed spectra of highly charged zinc ions from a variety of laser-produced plasmas. High-precision measurements of transition wavelengths have been made in the range 6.7–8.6 A, with accuracies of ≈1 mA. Line identifications for high-n transitions (n ≤ 7) in the N-, O-, and F-like spectra of Zn XXIV, XXIII, XXII, respectively, are made by comparison with steady-state collisional–radiative models.

The University of Nevada, Reno has developed a collisional-radiative atomic kinetics model that has successfully described the spectra produced by widely different multicharged ion experiments. The application of the model to experiments that highlight the importance of particular kinetics effects, including time-dependence and non-Maxwellian electron distribution functions, will be presented. These experiments include ion beam collision and high-temperature femtosecond laser and X-pinch plasma experiments. Adequate descriptions of ion beam collision spectra and x-ray yield require time-dependent treatment of radiative cascades from high-n capture states. Spectra from plasmas with significant fractions of hot electrons, such as those produced by fs lasers and X-pinches, require calculation of hot electron effects on collisional rates. The kinetics model presented here extracts as much information as possible from advanced experimental diagnostics such as time- and space-resolved spectral measurements.

We develop an integrated instrumental and computational package for the diagnosis of impurity content, Zeff profile, particle transport, and magnetohydrodynamics activity in magnetic fusion experiment plasmas. The package includes broadband filtered arrays of absolute (AXUV) photodiodes, a transmission grating imaging spectrometer measuring up to 20 chords across the discharge and having a few angstrom spectral resolution, together with an atomic physics database coupled with an impurity transport code. The atomic physics database is based on ab initio computations with the Hebrew University Lawrence Livermore atomic code. The package is designed for the diagnostic of sub-keV plasmas having predominantly low-Z impurities (C, B, and O) together with trace metals. A preliminary version is being tested on the National Spherical Torus Experiment spherical torus at the Princeton Plasma Physics Laboratory, using the ultrasoft x-ray imaging system and a grazing incidence spectrometer. Representative results from...

The current ramp down phase of the Frascati Tokamak Upgrade plasma has been found to exhibit very different particle transport than that which is observed in the Ohmically heated steady state phase. The current ramp down phase can be characterized by a central (r/a 0.5) that has transport two to three times less. The temperature in the inner region had a Gaussian-like shape as a function of minor radius. In the outer region, the temperature had roughly a single value (~100 eV) with no sharp gradients which implied no gradient driven transport. To study the particle transport, iron was introduced into the ramp down phase by using the laser blow off technique. The time behaviour of several charge states of iron have been measured spectroscopically to determine the transport in the different spatial locations in the plasma. The time histories of the charge state line emission in the ramp down phase have been observed to decay much more slowly than in the steady state phase which implied the existence of a transport barrier at the half radius. The behaviour of the impurity charge states has been modelled with the MIST transport code using up to date atomic physics rates to infer the particle transport.

Spectra in the 7.50-8.70???range from highly charged copper ions are analysed, and line identifications are made for the Na-, Ne-, F- and O-like charge states. The spectra are recorded with a spherically bent crystal spectrometer using either a mica or quartz crystal for moderate (?/?? = 3000) and high (?/?? = 8000) energy resolution, respectively. The plasmas from which the spectra are emitted are formed with either a Nd:glass (15?ns pulse) or a XeCl (12?ns pulse) laser. Systematic variations in the observed spectra with pulse energy are studied. Using different laser energies, and defocusing of the laser to reduce the intensity, we create plasmas with different ionization state distributions, which allows us to deconvolve blended lines from different copper ions. Line identifications are made based on relativistic atomic structure calculations that account for configuration interaction in level energies and transition rates. We use full kinetics simulations of ion emissivities, not just calculations of theoretical transition energies, to identify the strong and weak lines in crowded spectral regions. We identify 2p-n? transitions for Ne-like Cu19+ for 4?n?8 and 2s-np transitions for 4?n?6. We offer the first identification of high-n (n?8) Na-like satellites to Ne-like Rydberg resonance lines. The first and second ionization energies for Cu19+ are found, at 1689.02 and 1709.16?eV, respectively, based on our observations.

Review of scientific instruments 88(5), 053501 (2017). doi:10.1063/1.4982166, Tuning the energy of an x-ray probe to an absorption line or edge can provide material-specific measurements that are particularly useful for interfaces. Simulated hard x-ray images above the Fe K-edge are presented to examine ion diffusion across an interface between Fe$_2$O$_3$ and SiO$_2$ aerogel foam materials. The simulations demonstrate the feasibility of such a technique for measurements of density scale lengths near the interface with submicron spatial resolution. A proof-of-principle experiment is designed and performed at the Linac coherent light source facility. Preliminary data show the change of the interface after shock compression and heating with simultaneous fluorescence spectra for temperature determination. The results provide the first demonstration of using x-ray imaging at an absorption edge as a diagnostic to detect ultrafast phenomena for interface physics in high-energy-density systems., Published by American Institute of Physics, [S.l.]

A long duration high fluence x-ray source has been developed at the National Ignition Facility (NIF). The target was a 14.4 mm tall, 4.1 mm diameter, epoxy walled, gas filled pipe. Approximately 1.34 MJ from the NIF laser was used to heat the mixture of (55:45) Kr:Xe at 1.2 atm (∼5.59 mg/cm3) to emit in a fairly isotropic radiant intensity of 400–600 GW/sr from the Ephoton = 3–7 keV spectral range for a duration of ≈ 14 ns. The HYDRA simulated radiant intensities were in reasonable agreement with experiments but deviated at late times.

This work describes measurements of laser propagation through very low-density aerogels and subsequent multi-keV photon production from titanium foils. For efficient foil heating, SiO 2 aerogel with densities of 2 and 5 mg/cm 3 have been cast into a plastic cylinder, which are then mounted to Ti foils that are 3–20 μm thick. Experiments have been performed on the GEKKO-XII laser facility to characterize laser propagation through the aerogel and X-ray production from the Ti foil. Multi-keV emission is diagnosed with a full set of diagnostics giving laser-to-X-ray conversion efficiencies, time-dependent X-ray power and two-dimensional X-ray imaging.

1D spectral imaging was used to characterize the K-shell emission of Z ≈ 30-35 and Z ≈ 40-42 laser-irradiated foils at the National Ignition Facility. Foils were driven with up to 60 kJ of 3ω light, reaching laser irradiances on target between 0.5 and 20 × 10(15) W/cm(2). Laser-to-X-ray conversion efficiency (CE) into the Heα line (plus satellite emission) of 1.0%-1.5% and 0.15%-0.2% was measured for Z ≈ 30-32 and Z ≈ 40-42, respectively. Measured CE into Heα (plus satellite emission) of Br (Z = 35) compound foils (either KBr or RbBr) ranged between 0.16% and 0.29%. Measured spectra are compared with 1D non-local thermodynamic equilibrium atomic kinetic and radiation transport simulations, providing a fast and accurate predictive capability.

A very large area (7.5 mm(2)) laser-driven x-ray backlighter, termed the Big Area BackLighter (BABL) has been developed for the National Ignition Facility (NIF) to support high energy density experiments. The BABL provides an alternative to Pinhole-Apertured point-projection Backlighting (PABL) for a large field of view. This bypasses the challenges for PABL in the equatorial plane of the NIF target chamber where space is limited because of the unconverted laser light that threatens the diagnostic aperture, the backlighter foil, and the pinhole substrate. A transmission experiment using 132 kJ of NIF laser energy at a maximum intensity of 8.52 × 10(14) W/cm(2) illuminating the BABL demonstrated good conversion efficiency of3.5% into K-shell emission producing ~4.6 kJ of high energy x rays, while yielding high contrast images with a highly uniform background that agree well with 2D simulated spectra and spatial profiles.

Experimental VUV spectra from the JET tokamak and from the reversed field pinch RFX have been simulated. For the former device both n = 2 to n = 2 L-shell Ar and Ne spectra (respectively, in the 14.5-43.0 and in the 35.0-80.0 nm ranges) were considered, whereas for RFX only the Ne spectrum was available. The spectra have been observed with the SPRED spectrometer. From the simulation of the spectra, relative sensitivity curves have been obtained for each instrument in the ranges of the simulation. For RFX only, it has been possible to extend this curve from ~13.0 to ~105 nm, by simulating intrinsic C and O emissions. The photon emission coefficients of the lines with wavelengths in the ranges of the experimental spectra were obtained from collisional-radiative models. For Ar and Ne these coefficients have been calculated by the Hebrew University Lawrence Livermore Atomic Codes atomic physics codes, whereas for C and O the corresponding coefficients have been taken from the `Atomic Data and Analysis Structure' database. Impurity modelling is performed using a one-dimensional impurity transport code, calculating for each atomic species the radial distribution of the impurity ions. The line brightnesses are evaluated in a post-processing subroutine and the simulations of the spectra are obtained. The spectral simulations (including impurity ion transport) give confidence in the atomic physics calculations, and allow the determination of the transport coefficients in the plasma regions from which the considered ionization states emit. Finally, the obtained relative sensitivity curves of the two SPRED spectrometers have been compared with the calibrations performed by means of the branching ratio technique.

We present measurements of density-sensitive extreme-ultraviolet line ratios from highly charged L-shell iron ions in the Frascati Tokamak Upgrade plasma at densities more than a factor of 2 higher than previously observed. These observations are directly applicable to recent measurements of emission from high-density regions of the atmospheres of W Ursae Majoris binary stars and DQ Herculis type cataclysmic variables. We compare our observations to collisional-radiative models with large atomic structure data sets computed with the HULLAC suite of codes. We find good agreement for nearly all cases where spectral blending does not compromise our data. We also compare the predictions of our HULLAC models with ratios given by the Brickhouse, Raymond, & Smith code; we find agreement to better than 20% between the two calculations independent of the size of the atomic model. Our results confirm observations of very high electron densities (>1014 cm-3) in the coronae of 44i Boo and EX Hya.

We present X-ray spectroscopic measurements of the ionization balance in inertial confinement fusion hohlraums supported by 4 ω Thomson scattering diagnostics. The experimental data show agreement with non-LTE radiation-hydrodynamic calculations of the averaged Au charge state and electron temperatures. These findings are consistent with the successful integrated modeling of the hohlraum radiation fields. Comparisons with detailed synthetic spectra calculations show that the experimental ionization distribution is shifted indicating non-steady state kinetics.

We report on the characterization of plasmas produced by ultrashort laser irradiation of 500 A thick layers of NaF buried at varying depths in plastic to reduce plasma gradients. The targets are irradiated with 130 fs , ≈170 mJ laser pulses (λ=400 nm ) at an intensity of ≈2×10 18 W cm −2 . The data are spectrally and temporally resolved, with resolutions of λ/Δλ≈1000 and ≳500 fs , respectively. We use X-ray emission spectroscopy to assess the electron density, Ne, and temperature, Te, in the plasma. The density is measured from Stark broadened line profiles of the He-like 1 1S– 3 1 P , He β , and H-like Lyβ lines of Na, while the temperature is determined from the intensity ratio of Na Heβ to Lyβ, and also from the dielectronic satellites to these lines. We find peak densities and temperatures of ≳10 23 cm −3 and ≈400 eV , respectively, at 2– 4 ps after the laser pulse. The plasma conditions plateau near these values for 5 ps after that. Atomic data for the kinetics simulations are generated with the HULLAC suite of codes. The Stark broadened line profiles, with full accounting of satellite transitions, are computed with the TOTAL code. Self-absorption effects are included along the observation line of sight using the radiation transport code CRETIN. Steady-state, non-LTE equilibrium plasma conditions are demonstrated suggesting that buried-layer experiments can be used as a test bed to study equation of state and opacity properties in hot, near-solid density matter.

We present the Δn = 0 (n = 3 to n = 3) EUV spectra of M-shell iron ions from a tokamak plasma obtained during the "ramp-down" phase of the discharge. The fractional ion abundances for K-like Fe+7 to Si-like Fe+12 are found from fitting model spectra to the measured spectrum. The plasma temperature is measured as a function of position by Thomson scattering of laser light and Langmuir probes. Collisional-radiative simulations have been computed for the above ions, using atomic data generated with the HULLAC suite of codes. The blended M-shell spectrum is strongly sensitive to temperature; this makes it a potentially useful diagnostic for observations of stellar coronae where the differential emission measure is dominated by temperatures around 1 MK.