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Analytic fits to the recommended electron-impact excitation and ionization cross sections for Be I are presented. The lowest 19 terms of configurations 2 s n l ( n ≤ 4) and 2 p 2 terms below the first ionization limit are considered. The fits are based on the accurate calculations with the convergent close coupling (CCC) method as well as the B-spline R-matrix (BSR) approach. The fitted cross sections provide rate coefficients that are believed to approximate the original data within 10% with very few exceptions. The oscillator strengths for the dipole-allowed transitions between all the considered states are calculated with the relativistic multi-configuration Dirac–Hartree–Fock (MCDHF) approach and compared with the CCC and BSR results. This comparison shows a very good agreement except for a handful of cases with likely strong cancellations.

Degenerate plasmas, in which quantum effects dictate the behavior of free electrons, are ubiquitous on earth and throughout space. Transitions between bound and free electron states determine basic plasma properties, yet the effects of degeneracy on these transitions have only been theorized. Here, we use an x-ray free electron laser to create and characterize a degenerate plasma. We observe a core electron fluorescence spectrum that cannot be reproduced by models that ignore free electron degeneracy. We show that degeneracy acts to restrict the available electron energy states, thereby slowing the rate of transitions to and from the continuum. We couple degeneracy and bound electron dynamics in an existing collisional-radiative code, which agrees well with observations. The impact of the shape of the cross section, and hence the magnitude of the correction due to degeneracy, is also discussed. This study shows that degeneracy in plasmas can significantly influence experimental observables such as the emission spectra, and that these effects can be included parametrically in well-established atomic physics codes. This work narrows the gap in understanding between the condensed-matter and plasma phases, which coexist in myriad scenarios.

Local-thermodynamic-equilibrium (LTE) K-shell spectroscopy is a common tool to diagnose electron density, ne, and electron temperature, Te, of high-energy-density (HED) plasmas. Knowing the accuracy of such diagnostics is important to provide quantitative conclusions of many HED-plasma research efforts. For example, Fe opacities were recently measured at multiple conditions at the Sandia National Laboratories Z machine (Bailey et al., 2015), showing significant disagreement with modeled opacities. Since the plasma conditions were measured using K-shell spectroscopy of tracer Mg (Nagayama et al., 2014), one concern is the accuracy of the inferred Fe conditions. In this article, we investigate the K-shell spectroscopy model uncertainties by analyzing the Mg spectra computed with 11 different models at the same conditions. We find that the inferred conditions differ by ±20–30% in ne and ±2–4% in Te depending on the choice of spectral model. Also, we find that half of the Te uncertainty comes from ne uncertainty. To refine the accuracy of the K-shell spectroscopy, it is important to scrutinize and experimentally validate line-shape theory. We investigate the impact of the inferred ne and Te model uncertainty on the Fe opacity measurements. Its impact is small and does not explain the reported discrepancies.

A minority relativistic electron component can arise in both laboratory and naturally occurring plasmas. In the presence of high-atomic-number ion species, the ion charge state distribution at a low bulk electron temperature can be dominated by relativistic electrons, even though their density is orders of magnitude lower. This is due to the relativistic enhancement of the collisional excitation and ionization cross sections. The resulting charge state effect can dramatically impact the radiative power loss rate and the related Bethe stopping power of relativistic electrons in a dilute plasma.

K shell X-ray emission measurements have been used to diagnose plasma conditions in short-pulse heated buried microdot targets on the Orion high power laser. These experiments have been used to validate simulations of short pulse laser-solid interaction that combine hybrid PIC modelling of the laser absorption with radiation-hydrodynamics simulations including an electron transport model. Comparison of these simulations with streaked K shell spectroscopy show the importance of including radial gradients in fitting the spectra. An example is presented of the emission of sulphur from a 50 µm diameter microdot sample buried in a plastic foil. Previously agreement between simulation and experiment was obtained only by treating the absorbed energy, electron temperature and beam divergence as fitting parameters. The good agreement obtained in this work used the measured laser energy and laser pulse length and calculated the laser-solid target interaction from first principles.

With the development of X-ray free electron lasers (XFEL), a novel state of matter of highly transient and non-equilibrium plasma has been created in laboratories. As high intensity X-ray laser beams interact with a solid density target, electrons are ionized from inner-shell orbitals and these electrons and XFEL photons create dense and finite temperature plasmas. In order to study atomic processes in XFEL driven plasmas, the atomic kinetics model SCFLY containing an extensive set of configurations needed for solid density plasmas was applied to study atomic processes of XFEL driven systems. The code accepts the time-dependent conditions of the XFEL as input parameters, and computes time-dependent population distributions and ionization distributions self-consistently with electron temperatures and densities assuming an instantaneous equilibration of electron energies. The methods and assumptions in the atomic kinetics model and unique aspects of atomic processes in XFEL driven plasmas are described.

For the first two Spectral Line Shapes in Plasma workshops, participants submitted in total over 1,500 line-shape calculations. The studies collected in this Special Issue explore only a part of this immense work. This book is a reprint of the special issue that appeared in the online open access journal Atoms (ISSN 2218-2004) in 2014 (available at: http://www.mdpi.com/journal/atoms/special_issues/SpectralLineShapes).

We present the main results of the 7th Non-Local Thermodynamic Equilibrium Code Comparison Workshop held in December 2011 in Vienna, Austria. More than twenty researchers from nine countries, who actively work on development of collisional-radiative codes for plasma kinetics modeling, attended the meeting and submitted their results for a number of comparison cases. The cases included free-electron-laser-inspired time-dependent relaxation of photoexcited Ne-like Ar, ionization balance and spectra for highly charged tungsten, spectroscopic diagnostics of krypton L-shell spectra, and an investigation of Ne model convergence with principal quantum number.

We report a recent experiment where the first hard x-ray beam line, X-ray Pump Probe (XPP) instrument using the SLAC National Accelerator Laboratory's Linac Coherent Light Source (LCLS) free electron laser, was used to heat thin foils to high energy densities ∼ 107 J/cm 3. An intense 9 keV, 60 fs (FWHM) duration beam with energy of 2 - 4 mJ at the XPP beam line was focused using beryllium lenses to an irradiance approaching 1016 Wcm -2. Targets of 0.5 - 3.5 μm thick foils of Ag and Cu were studied using a suite of diagnostics including Fourier Domain Interferometry, energy calorimetry and grating and crystal spectrometers. The experimental details and spectroscopic results from the campaign will be described. Preliminary results indicate that the target is heated relatively uniformly to a temperature lower than 20 eV. © 2011 SPIE.

Short pulse (< 100 fs) tunable X-ray and VUV laser sources, based on the free electron laser (FEL) concept, will be a watershed for high energy density research in several areas. These new 4th generation light sources will have extremely high fields and short wavelength (~0.1 nm) with peak spectral brightness -photons/(s/mrad2/mm2/0.1% bandwidth- 1010 greater than 3rd generation light sources. We briefly discuss several applications: the creation of warm dense matter (WDM), probing of near solid density plasmas, and laser-plasma spectroscopy of ions in plasmas. The study of dense plasmas has been severely hampered by the fact that laser-based probes that can directly access the matter in this regime have been unavailable and these new 4th generation sources will remove these restrictions. Finally, we present the plans for a user-oriented set of facilities that will incorporate high-energy, intense short-pulse, and x-ray lasers at the first x-ray FEL, the LCLS to be opened at SLAC in 2009.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Physical review letters 109, 245003 (2012). doi:10.1103/PhysRevLett.109.245003, Published by APS, College Park, Md.

The possibility of creating hot-dense plasma samples by isochoric heating of solid targets with high-intensity femtosecond X-ray lasers has opened up new opportunities in the experimental study of such systems. A study of the X-ray spectra emitted from solid density plasmas has provided significant insight into the X-ray absorption mechanisms, subsequent target heating, and the conditions of temperature, electron density, and ionization stages produced (Vinko et al., Nature 482, 59–62 (2012)). Furthermore, detailed analysis of the spectra has provided new information on the degree of ionization potential depression in these strongly coupled plasmas (Ciricosta et al., Phys. Rev. Lett. 109, 065002 (2012)). Excellent agreement between experimental and simulated spectra has been obtained, but a full outline of the procedure by which this has been achieved has yet to be documented. We present here the details and approximations concerning the modelling of the experiment described in the above referenced work. We show that it is crucial to take into account the spatial and temporal gradients in simulating the overall emission spectra, and discuss how aspects of the model used affect the interpretation of the data in terms of charge-resolved measurements of the ionization potential depression.

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

Collisional-radiative (CR) models are used to obtain atomic level population distributions and radiative properties in plasmas. These quantities are used to help design experiments, to provide data for radiative energy transport in radiation-hydrodynamic simulations, and to diagnose laboratory and astrophysical plasmas whose conditions are difficult to or impossible to directly measure. CR models are constructed by coupling a set of electronic energy levels with spontaneous, collisional, and radiation-driven transitions . Since the number of atomic levels and transitions necessary to build a CR model can be prohibitively high, especially for many-electron ions, models are often customized for specific applications by tailoring the structure based on expected plasma conditions. On the other hand, there remains a need for models that are general enough to predict charge state distributions and radiative properties with reasonable accuracy for plasmas over a wide range of plasma conditions. Such generalized models are especially useful for design simulations, which access a wide range of conditions, and for preliminary analysis of spectroscopic data. This chapter describes a class of generalized CR models based on screened-hydrogenic atomic levels and rates. These models have been applied to a wide variety of applications and have demonstrated reliable performance over a wide range of plasma conditions, from the low-density coronal limit to local thermodynamic equilibrium.

X-ray free-electron lasers (XFELs) provide unique opportunities to generate and investigate dense plasmas. The absorption and transmission properties of x-ray photons in dense plasmas are important in characterizing the state of the plasmas. Experimental evidence shows that the transmission of x-ray photons through dense plasmas depends greatly on the incident XFEL intensity. Here, we present a detailed analysis of intensity-dependent x-ray transmission in solid-density aluminum using collisional-radiative population kinetics calculations. Reverse saturable absorption (RSA), i.e., an increase in x-ray absorption with intensity has been observed for photon energies below the K-absorption edge and in the intensity range of 1016–1017 W/cm2 for XFEL photons with 1487 eV. At higher intensities, a transition from RSA to saturable absorption (SA) is predicted; thus, the x-ray absorption decreases with intensity above a threshold value. For XFEL photon energies of 1501 eV and 1515 eV, the transition from RSA to SA occurs at XFEL intensities between 1017–1018 W/cm2. Electron temperatures are predicted to be in the range of 30–50 eV for the given experimental conditions. Detailed population kinetics of the charge states explains the intensity-dependent absorption of x-ray photons and the fast modulation of XFEL pulses for both RSA and SA.

M-Band and L-Band Gold spectra between 3 and 5 keV and 8 and 13 keV, respectively, have been recorded by a photometrically calibrated crystal spectrometer. The spectra were emitted from the plasma in the laser deposition region of a ‘hot hohlraum’. This is a reduced-scale hohlraum heated with ≈9 kJ of 351 nm light in a 1 ns square pulse at the OMEGA laser. The space- and time-integrated spectra included L-Band line emission from Co-like to Ne-like gold. The three L-Band line features were identified to be the 3s → 2p, 3d5/2 → 2p3/2 and 3d3/2 → 2p1/2 transitions at ≈9 keV, ≈10 keV and ≈13 keV, respectively. M-Band 5f → 3d, 4d → 3p, and 4p → 3s transition features from Fe-like to P-like gold were also recorded between 3 and 5 keV. Modeling from the radiation–hydrodynamics code LASNEX, the collisional-radiative codes FLYCHK and SCRAM, and the atomic structure code FAC were used to model the plasma and generate simulated spectra for comparison with the recorded spectra. Through these comparisons, we have determined the average electron temperature of the emitting plasma to be between 6.0 and 6.5 keV. The electron temperatures predicted by LASNEX appear to be too large by a factor of about 1.5.

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

A method to compute collisional excitation cross-sections in jj-averaged configuration sets is presented in the framework of plane-wave Born approximation using Dirac–Hartree–Slater wave functions with appropriate low-energy corrections. When averaged into the ls configuration or hydrogenic superconfiguration sets, the results are found to compare with distorted wave calculations well within 30% on average. The cross-sections are averaged into hydrogenic cross-sections and fitted using the Gaunt factor formalism. We present analytic fit coefficients of Gaunt factors for 12 atoms of Z between 5 and 79 for hydrogenic transitions.

High temperature (“hot”) hohlraums are being developed to heat samples to high temperatures for opacity or other atomic physics studies. Hot hohlraums have been fielded at the National Ignition Facility [D.E. Hinkel, et al., Phys. Plasmas 12 (2005) 056305] and the OMEGA [M.B. Schneider, et al., Phys. Plasmas 13 (2006) 112701] lasers. They reach high radiation temperatures by coupling a maximum amount of laser energy (10 kJ) into small, i.e., 400–800 μm diameter, gold hohlraums in a 1 ns pulse causing the hohlraums to fill with gold plasma. Radiation temperatures of 370 eV have been measured in the laser entrance hole (LEH) region of these targets [D.E. Hinkel, et al., Phys. Rev. Lett. 96 (2006) 195001]. However, the LEH radiation is not the radiation drive of interest as the sample can neither be shielded from the non-thermal components of this radiation nor protected from the gold plasma. To mitigate these problems the source we are developing uses the radiation from the X-ray burnthrough of thin walls of a pair of hot hohlraums to heat a sample. We report on the measured radiation drive of this source and its use to heat a surrogate sample. We characterize the radiative heating of the sample by measuring its thermal expansion.

We present the first highly resolved measurements of the plasmon spectrum in an ultrafast heated solid. Multi-keV x-ray photons from the Linac Coherent Light Source have been focused to one micrometer diameter focal spots producing solid density aluminum plasmas with a known electron density of n_{e}=1.8×10^{23} cm^{-3}. Detailed balance is observed through the intensity ratio of up- and down-shifted plasmons in x-ray forward scattering spectra measuring the electron temperature. The plasmon damping is treated by electron-ion collision models beyond the Born approximation to determine the electrical conductivity of warm dense aluminum.

For plasmas containing high-Z ions the energy loss due to radiative processes can be important in understanding energy distributions and spectral characteristics. Since high-Z plasmas occur over a wide range of temperature and density conditions, a general non-LTE population kinetics description is required to provide a qualitative and quantitative description for radiative energy loss. We investigate radiative properties of non-LTE krypton plasmas with a collisional–radiative (CR) model constructed from detailed atomic data. This work makes two extensions beyond previous non-LTE kinetics models. First, this model explicitly treats the dielectronic recombination (DR) channels. Second, this model allows one to investigate the higher electron density regimes found commonly in laboratory plasmas. This more comprehensive approach enables the study of population kinetics in a general manner and will provide a systematic guide for reducing a complex model to a simpler one. Specifically, we present the calculations of radiative cooling coefficients of krypton ions as a function of electron density in the optically thin limit. Total, soft X-ray (1.6 keV ≤ E ≤ 12 keV), and hard X-ray (E ≥ 12 keV) radiative cooling coefficients are given for the plasma conditions of 0.6 keV ≤ Te ≤ 10 keV and 1014 cm−3 ≤ Ne ≤ 1024 cm−3. The ionic radiative cooling coefficients provided are sufficient to allow users to construct the total rate from given charge state distributions. Steady-state calculations of the average charge state at given Te and Ne values are also presented.

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 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.

Outstanding discrepancies between data and calculations of laser-produced plasmas in recombination have been observed since the 1980s. Although improvements in hydrodynamic modeling may reduce the discrepancies, there are indications that non-LTE atomic kinetics may be the dominant cause. Experiments to investigate non-LTE effects were recently performed at the NIKE KrF laser on low-density Ti-doped aerogels. The laser irradiated a 2 mm diameter, cylindrical sample of various lengths with a 4-ns square pulse to create a volumetrically heated plasma. Ti L-shell spectra spanning a range of 0.47–3 keV were obtained with a transmission grating coupled to Si photodiodes. The diagnostic can be configured to provide 1-dimensional spatial resolution at a single photon energy, or 18 discrete energies with a resolving power, λ / δ λ of 3–20. The data are examined and compared to calculations to develop absolute emission measurements that can provide new tests of the non-LTE physics.

High-resolution X-ray spectra were recorded by the High-Energy Electronic X-ray (HENEX) spectrometer from a variety of targets irradiated by the Omega laser at the Laboratory for Laser Energetics. The HENEX spectrometer utilizes four reflection crystals covering the 1–20 keV energy range and one quartz(1 0 −1 1) transmission crystal (Laue geometry) covering the 11–40 keV range. The time-integrated spectral images were recorded on five CMOS X-ray detectors. In the spectra recorded from krypton-filled gasbag and hohlraum targets, the helium-like K-shell transitions n = 1 – 2 , 1–3, and 1–4 appeared in the 13–17 keV energy range. A number of additional spectral features were observed at energies lower than the helium-like n = 1 – 3 and n = 1 – 4 transitions. Based on computational simulations of the spectra using the FLYCHK/FLYSPEC codes, which included opacity effects, these additional features are identified to be inner-shell transitions from the Li-like through N-like krypton charge states. The comparisons of the calculated and observed spectra indicate that these transitions are characteristic of the plasma conditions immediately after the laser pulse when the krypton density is 2×1018 cm−3 and the electron temperature is in the range 2.8–3.2 keV. These spectral features represent a new diagnostic for the charge state distribution, the density and electron temperature, and the plasma opacity. Laboratory experiments indicate that it is feasible to record K-shell spectra from gold and higher Z targets in the >60 keV energy range using a Ge(2 2 0) transmission crystal.

FLYCHK is a straightforward, rapid tool to provide ionization and population distributions of plasmas in zero dimension with accuracy sufficient for most initial estimates and in many cases is applicable for more sophisticated analysis. FLYCHK solves rate equations for level population distributions by considering collisional and radiative atomic processes. The code is designed to be straightforward to use and yet is general enough to apply for most laboratory plasmas. Further, it can be applied for low-to-high Z ions and in either steady-state or time-dependent situations. Plasmas with arbitrary electron energy distributions, single or multiple electron temperatures can be studied as well as radiation-driven plasmas. To achieve this versatility and accuracy in a code that provides rapid response we employ schematic atomic structures, scaled hydrogenic cross-sections and read-in tables. It also employs the jj configuration averaged atomic states and oscillator strengths calculated using the Dirac–Hartree–Slater model for spectrum synthesis. Numerous experimental and calculational comparisons performed in recent years show that FLYCHK provides meaningful estimates of ionization distributions, well within a charge state for most laboratory applications.

The K-shell spectroscopy code FLY and its predecessors have been employed to study hot dense plasmas for decades. FLY has provided a basis for studies of K-shell ions up to Z=26, where its ease of use, PC application base, and synthetic spectral production have made it attractive to both experimentalists and modelers. However, the application has been focused on K-shell ions where less ionized species are represented as a ground state only. To attempt to make this simple model predict the ionization and recombination through the less ionized stages, we extend the model to include kinetics models for all ion stages. The emphasis of this extension is not to provide detailed spectra or population for the L- or M-shell, but to provide a K-shell model with enhanced accuracy in those cases where ionization and recombination through the L- and M-shell are important. This work is a first step in generating an application that will allow detailed analysis of sub-picosecond self-consistent velocity distribution and population kinetics solutions. We will discuss the extensions and provide examples. Finally, we will outline the progress towards the eventual goal of the self-consistent solution.

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.

The intensities within the focal spots of the output of recently developed X-ray sources based on free-electron-laser (FEL) technology are so great that atoms within the focal region can potentially absorb several photons during the few tens of femtosecond X-ray pulse. Furthermore, the duration of the FEL X-ray pulse is comparable to the Auger decay times of inner-shell holes created by the X-rays themselves. We report here how such a scenario can lead to opacity broadening of the fluorescence radiation emitted by the hot, dense plasma, which is created as a result of the X-radiation focussed onto a solid target, and in particular present calculations of the broadening of the Kα emission in a solid-density aluminium target, produced when the FEL photon energy is tuned below the Al K-edge, but is resonant with the Kα transition. © 2014 Elsevier B.V.

Underdense radiation sources have been developed to provide efficient laboratory multi-keV radiation sources for radiography and radiation hardening studies. In these plasmas laser absorption by inverse bremsstrahlung leads to high x-ray conversion efficiency because of efficient ionization of the low density aerogel or gas targets. Now we performing experiments in the soft x-ray energy regime where the atomic physics models are much more complicated. In recent experiments at the NIKE laser, we have irradiated a Ti-doped SiO 2 aerogel with up to 1650J of 248 nm wavelength light. The absolute Ti L-shell emission in the 200-800 eV range is measured with a diagnostic that uses a transmission grating coupled to Si photodiodes. We will give an overview of the temporally-resolved absolutely calibrated spectra obtained over a range of conditions. Eventually we hope to extend our studies to x-ray production in the EUV range.

International audience; With the advent of new x-ray light-sources worldwide, the creation of dense, uniformly heated plasma states arising from intense x-ray irradiation of solids has been made possible. In the early stages of x-ray solid heating, before significant hydrodynamic motion occurs, the matter exists in a highly non-equilibrium state. A method based on wavefront sensing is proposed to probe some of the fundamental properties of these states. The deflection and absorption of a high harmonic probe beam propagated through the plasma can be measured with a wavefront sensor, and allow for the determination of the complex refractive index (RI) of the plasma, giving a 2D map of the optical properties as function of time in a pump-probe arrangement. A solid heating model has been used to estimate the expected temperatures of x-ray heated thin foils, and these temperatures are used in three separate models to estimate the changes in the refractive index. The calculations show the changes induced on an extreme ultra-violet (XUV) probe beam by a solid density thin foil plasma are significant, in terms of deflection angle and absorption, to be measured by already existing XUV Hartmann wavefront sensors. The method is applicable to a wide range of photon energies in the XUV (10s to several 100s of eV) and plasma parameters, and can add much needed experimental data to the fundamental properties of such dense plasma states. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794964]

We have utilized a newly developed high-resolution X-ray spectrometer to measure the shapes of spectral lines produced from laser-irradiated targets on the Orion laser facility in the United Kingdom. We present measurements of the He-β spectra of chlorine and chromium from targets irradiated by either a long-pulse or a short-pulse laser beam. The experimental conditions provide a spread in plasma density ranging from about 1019 to about 1024 cm−3. We present spectral calculations that show that the relative intensities of the Li-like satellite lines can be used to infer the density in the lower range, especially if the lithiumlike satellite lines are well resolved. In addition, we use the Stark-broadened width of the He-β line to infer densities above about 1022 cm−3. In the case of a short-pulse irradiated chromium foil, we find that the He-like chromium is produced at a density of almost 8 g/cm3, i.e., solid density. In addition, we can infer the electron temperature from the observation of dielectronic...

We have used the Linac Coherent Light Source to generate solid-density aluminum plasmas at temperatures of up to 180 eV. By varying the photon energy of the x rays that both create and probe the plasma, and observing the $K\mathrm{\text{\ensuremath{-}}}\ensuremath{\alpha}$ fluorescence, we can directly measure the position of the $K$ edge of the highly charged ions within the system. The results are found to disagree with the predictions of the extensively used Stewart-Pyatt model, but are consistent with the earlier model of Ecker and Kr\"oll, which predicts significantly greater depression of the ionization potential.

We present simulations of the charge states produced by the interaction of intense X-ray laser radiation with a neon gas. We model the results of a recent experiment (Young et al., Nature 466, 56 (2010)), where mJ pulses of X-rays, with photon energies ranging from 800 to 2000 eV and pulse lengths ranging from 70 to 340 fs were incident on neon atoms at intensities of up to 10 18 W cm -2. Simulations using an adapted version of the SCFLY collisional-radiative code, which included the effect of electron collisions and a simple self-consistent temperature model, result in charge state distributions that are in good agreement with the experimental data. We calculate the electron temperature of the system during the evolution of the plasma, and comment upon the role that collisions may play in determining the charge state distributions as a function of the neon ion number density. © 2011 Elsevier B.V.

We report on the use of high energy X-ray laser at 21 nm in novel applications relevant to dense plasma physics. Our recent results include e.g. high resolution plasma backlighting and production of warm dense matter.

Three independent methods (extreme ultraviolet spectroscopy, imaging at 68 and 256 eV) have been used to measure planar target rear surface plasma temperature due to heating by hot electrons. The hot electrons are produced by ultraintense laser-plasma interactions using the 150 J, 0.5 ps Titan laser. Soft x-ray spectroscopy in the 50-400 eV region and imaging at the 68 and 256 eV photon energies give a planar deuterated carbon target rear surface pre-expansion temperature in the 125-150 eV range, with the rear plasma plume averaging a temperature approximately 74 eV.

A high contrast 12.6 keV Kr K alpha source has been demonstrated on the petawatt-class Titan laser facility using strongly clustering Kr gas jet targets. The contrast ratio (K alpha to continuum) is 65, with a competitive ultrashort pulse laser to x-ray conversion efficiency of 10(-5). Filtered shadowgraphy indicates that the Kr K alpha and K beta x rays are emitted from a roughly 1x2 mm(2) emission volume, making this source suitable for area backlighting and scattering. Spectral calculations indicate a typical bulk electron temperature of 50-70 eV (i.e., mean ionization state 13-16), based on the observed ratio of K alpha to K beta. Kr gas jets provide a debris-free high energy K alpha source for time-resolved diagnosis of dense matter.

Acquisition of three-dimensional (3D) spatially localized, water-suppressed one-dimensional (1D) 1H MR spectra has been optimized in human tissues over the last two decades [1–6]. Introduction of automated MRS a decade ago has enabled a 1–2 min pre-scan to calibrate the flipangle using the transmitter power, to adjust the static field homogeneity (B0) using the linear gradient shim coils, and to optimize water suppression, which used to be an at least 15 min operation, facilitating the integration of clinical MRS protocols into routine MRI examinations [7]. In 1H MR spectroscopy of human brain, spectral resonances due to methyl, methylene, and methine protons of N-acetylaspartate (NAA), glutamate/glutamine (Glx), creatine (Cr), choline (Ch), myo-inositol (mI), GABA, aspartate (Asp), N-acetylaspartyl-glutamate (NAAG), and other metabolites have been identified in the region of 0–4.5 ppm [2–12]. One-dimensional MRS in vivo is hampered by the fact that it is difficult to resolve a multitude of peaks existing over a small spectral range of approximately 300 Hz at 1.5 T. Spectral overlap of macromolecules, GABA, and glutathione with the methyl resonances of NAA, Cr, NAAG, and methylene resonances of Glx has also been reported [8,14–15]. Attempts have been made to quantify Glx [16], glucose [17], and other metabolites with only minimal success due to the difficulty in extracting this information from a region with many overlapping resonances. Using spectral-editing techniques, it is possible to select a particular J -coupled metabolite [2,14,18– 20]. However, one major drawback of editing techniques is that only one metabolite is optimized at a time assuming that the multiplets of the J -coupled metabolites are well separated. Using the LC-Model post-processing algorithm, quantification of several metabolites in human brain in vivo has been reported recently using a basis-set of 10–20 different metabolite spectra in vitro [21–23]. Unlike the spectral editing techniques, which target one metabolite at a time, two-dimensional (2D) MRS can unambiguously resolve many overlapping peaks nonselectively in vitro as shown by Ernst and co-workers two decades ago using the vertical bore NMR spectrometers [24–25]. 2D-MR spectroscopy enables converting a crowded overlapping 1D MR spectrum to a betterresolved 2D spectrum through the addition of a spectral dimension. Instead of a standard 1D spectrum plotting intensity vs. a single-axis (i.e. chemical shift), 2D MR spectroscopy techniques produce a 2D spectrum plotting intensity vs. two axes, the dimensions of which depend on the specific 2D MR technique [25]. Better dispersion of several metabolite peaks and improved spectral assignment make the proposed technique more attractive. It seems natural to explore the clinical potentials of 2D MRS techniques of human tissues in vivo. There have been several attempts during the last 15 years in the implementation and evaluation of 2D NMR spectroscopy on in vivo MRI scanners and MR spectrometers [26–30]. The aim of this chapter is to discuss the recent progress on the implementation of selected localized 2D MRS sequences on the whole body 1.5 T and higher field MRI scanners. This includes a summary of 1D spectroscopy with and without chemical shift imaging (CSI), followed by singleand multi-voxel based 2D spectroscopy dealing with coherent interactions such as chemical shift and J -coupling. A brief overview of potential artefacts in 2D spectroscopy and simulation is also included.

Measurements of the L -shell emission of highly charged gold ions were made under controlled laboratory conditions using the SuperEBIT electron beam ion trap, allowing detailed spectral observations of lines from Fe-like Au53+ through Ne-like Au69+ . Using atomic data from the Flexible Atomic Code, we have identified strong 3d_{52}-->2p_{32} emission features that can be used to diagnose the charge state distribution in high energy density plasmas, such as those found in the laser entrance hole of hot hohlraum radiation sources. We provide collisional-radiative calculations of the average ion charge Z as a function of temperature and density, which can be used to relate charge state distributions inferred from 3d_{52}-->2p_{32} emission features to plasma conditions, and investigate the effects of plasma density on calculated L -shell Au emission spectra.

We report the first direct measurements of total absorption of short laser pulses on solid targets in the ultrarelativistic regime. The data show an enhanced absorption at intensities above ${10}^{20}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$, reaching 60% for near-normal incidence and 80%--90% for 45\ifmmode^\circ\else\textdegree\fi{} incidence. Two-dimensional particle-in-cell simulations demonstrate that such high absorption is consistent with both interaction with preplasma and hole boring by the intense laser pulse. A large redshift in the second harmonic indicates a surface recession velocity of 0.035c.

The transient evolution of X-ray emission from high density plasmas usually terminates with a recombination regime at low density. For matter irradiated by short pulses (< 1 ps) the accumulation of x-ray emission at low density cannot be suppressed by streak camera techniques as current time resolution is limited (> 0.5 ps). We propose intrinsically fast x-ray signals realized by the radiation emission from hollow ion states K0Ln to temporally isolate high density information from the low density radiative recombination regime. Simulations carried out for short pulse (100 fs) intense x-ray free electron laser radiation (XFEL) interacting with dense plasmas demonstrate that the hollow ion x-ray emission "switch" has a time scale faster than 50 fs. Moreover, the time of the hollow-ion emission signal is related to the interaction time and is thus directly related only to the highest density regimes even if the usual time integrated spectroscopic techniques are employed.

We present measurements of the fast-electron-relaxation time in short-pulse (0.5 ps) laser-solid interactions for laser intensities of 10{sup 17}, 10{sup 18}, and 10{sup 19} W/cm{sup 2}, using a picosecond time-resolved x-ray spectrometer and a time-integrated electron spectrometer. We find that the laser coupling to hot electrons increases as the laser intensity becomes relativistic, and that the thermalization of fast electrons occurs over time scales on the order of 10 ps at all laser intensities. The experimental data are analyzed using a combination of models that include K{alpha} generation, collisional coupling, and plasma expansion.

Summary form only given. The production of MeV protons by intense lasers is an area of great topical interest particularly with respect to the proposal to use protons to initiate burn in a fusion capsule. Following successful initial studies of focusing protons with hemishell targets, using a 10 J, 100 fs laser we extended the study to higher energy and longer pulses using PW class lasers at the RAL Vulcan, ILE Gekko facilities. Proton focusing was significantly aberrated in these experiments where a relatively small laser focal spot produced a central maximum in the sheath extension giving radial components to the acceleration. Experimental studies of this effect will be discussed and compared to 2D hybrid PIC modeling. In addition recent 1D numerical modeling of proton conversion efficiency with the hybrid PIC code LSP are beginning to show promising results, namely increased conversion of electron energy to proton energy. These theoretical predictions are currently being experimentally tested with targets that increase the proportion of protons on the target surface compared to heavy ions. Conclusions from these studies will be present and discussed in the context of fast ignition

Hard x-ray spectra were recorded by the High Energy Electronic X-Ray (HENEX) spectrometer from a variety of targets irradiated by the Omega laser at the Laboratory for Laser Energetics. The HENEX spectrometer utilizes four reflection crystals covering the 1 keV to 20 keV energy range and one quartz(10-11) transmission crystal (Laue geometry) covering the 11 keV to 40 keV range. The time-integrated spectral images were recorded on five CMOS x-ray detectors. Spectra were recorded from gold and other metal targets and from krypton-filled gasbags and hohlraums. In the spectra from the krypton-filled targets, the helium-like K-shell transitions n=1-2, 1-3, and 1-4 appeared in the 13 keV to 17 keV energy range. A number of additional spectral features were observed at energies lower than the helium-like n=1-3 and n=1-4 transitions. Based on computational simulations of the spectra using the FLYCHW/FLYSPEC codes, which included opacity effects, these additional features are identified to be inner-shell transitions from the Li- like through N-like krypton charge states. The comparisons of the calculated and observed spectra indicate that these transitions are characteristic of the plasma conditions immediately after the laser pulse when the krypton density is 2x10 18 cm -3 and the electron temperature is in the range 2.8 keV to 3.2 keV. These spectral features represent a new diagnostic for determining the charge state distribution, the density and electron temperature, and the plasma opacity. The intense 13 keV krypton K-shell emission should be useful for backlighters and radiography of dense plasmas. Laboratory experiments indicate that it is feasible to record K-shell spectra from gold and higher Z targets in the > 60 keV energy range using a Ge(220) transmission crystal.

Summary form only given. Plasma spectroscopy is an important component for diagnosis and design of laboratory plasma experiments. The advent of plasma-generation devices such as laboratory and FEL-based X-ray lasers, intense ultra-short-pulse lasers, NIF and powerful Z-pinch machines will provide further impetus to develop fast, accurate plasma spectroscopic techniques. The new generation techniques must address the physical processes important to the production of exotic states of matter - such as warm dense matter, highly transient states of matter, and extremely hot dense matter - to develop an understanding of these novel plasmas. We have developed a simple, but generalized, non-LTE population kinetics and spectrum model that can be employed to study the plasma spectroscopy in most laboratory conditions. This capability, FLYCHK, will provide charge state distributions and synthetic spectra to help experimental design and spectral analysis. FLYCHK is designed with a view to being simple, easy-to-use, fast, and portable while providing a reasonable spectroscopic model for most users. We present the details of FLYCHK and provide examples relevant to several applications: laser-generated plasmas, EUV radiation modeling, EBIT plasmas, XFEL-generated plasmas

Summary form only given. The prediction of the emission radiated from high-Z ions in a plasma, i.e., the radiative yield, is important in understanding the distribution of energy as well as the spectral characteristics in plasmas with high-Z ions. Since these plasmas occur over a wide range of plasma conditions, they require a general non-LTE population kinetics description. A kinetics model is constructed using the atomic data generation capability of HULLAC to provide charge state distributions, level population distributions and radiative properties of laboratory plasmas. The constructed model explicitly treats the doubly-excited states and dielectronic recombination channels critical to charge state distributions. The use of the full non-LTE kinetics model permit us to investigate the higher electron density regimes, well beyond the coronal limit, found commonly in laboratory plasmas. Hence, with this construct we can use a single kinetics model to provide radiative yields from the coronal to the highest density regimes found in laboratories. To illustrate the capabilities of this approach we present the detailed calculations of total radiative cooling coefficients and the X-ray radiative cooling coefficients as a function of electron density from and well beyond the coronal limit.

We have successfully demonstrated spectrally-resolved x-ray scattering in a variety of dense plasmas as a powerful new technique for providing microscopic dense plasma parameters unattainable by other means. The results have also been used to distinguish between ionization balance models. This has led to 10 published or to be published papers, 8 invited talks and significant interest from both internal and external experimental plasma physicists and the international statistical plasma physics theory community.

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{sub e}>10{sup 22}cm{sup -3} as light propagation is severely altered by the plasma. The construction of the Tesla Test Facility(TTF) at DESY(Deutsche Elektronen-Synchrotron), a short pulse tunable free electron laser in the vacuum-ultraviolet and soft X-ray regime (VUV FEL), based on the SASE(self amplified spontaneous emission) process, will provide a major advance in the capability for dense plasma-related research. This source will provide 10{sup 13} photons in a 200 fs duration pulse that is tunable from {approx} 6nm to 100nm. Since an VUV FEL will not have the limitation associated with optical lasers the entire field of high density plasmas kinetics in laser produced plasma will then be available to study with tunable source. Thus, one will be able to use this and other FEL x-ray sources to pump individual transitions creating enhanced population in the excited states that can easily be monitored. We show two case studies illuminating different aspects of plasmamore » spectroscopy.« less

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 unprecedented values for the ionization parameter $\ensuremath{\xi}=20--25\text{ }\text{ }\mathrm{e}\mathrm{r}\mathrm{g}\text{ }\text{ }\mathrm{c}\mathrm{m}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ under near steady-state conditions. Line opacities are well fitted by a curve-of-growth analysis which includes the effects of velocity gradients in a one-dimensional expanding plasma. First comparisons of the measured charge state distributions with x-ray photoionization models show reasonable agreement.

The construction of short-pulse tunable soft x-ray free electron laser sources based on the self-amplified spontaneous emission process will provide a major advance in capability for dense plasma-related and warm dense matter (WDM) research. The sources will provide 1013 photons in a 200-fs duration pulse that is tunable from approximately 6 to 100 nm. Here we discuss only two of the many applications made possible for WDM that has been severely hampered by the fact that laser-based methods have been unavailable because visible light will not propagate at electron densities of ne ≥ 1022cm-3. The next-generation light sources will remove these restrictions. © 2003 Optical Society of America.