Biomedical subjects

K B Fournier

Publications and source records attributed to K B Fournier.

18 recordsLinked to original sources

PubMed2005

Temperature determination using Kalpha spectra from M -shell Ti ions.

The compact multipulse terawatt (COMET) laser facility at LLNL was used to irradiate Al-coated 2-50 microm Ti foils with approximately 10(19) W cm(-2) , 500 fs, 3-6 J laser pulses. Laser-plasma interactions on the front side of the target generate hot electrons with sufficient energy to excite inner-shell electrons in Ti, creating Kalpha emission which has been measured using a focusing spectrometer with spatial resolution aimed at the back surface of the targets. The spatial extent of the emission varies with target thickness. The high spectral resolution (lambda/Deltalambda approximately equal to 3800) is sufficient to measure broadening of the Kalpha emission feature due to the emergence of blueshifted satellites from ionized Ti in a heated region of the target. A self-consistent-field model is used to spectroscopically diagnose thermal electron temperatures up to 40 eV in the strongly coupled Ti plasmas.

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PubMed2005

Measurement of 2l-nl' x-ray transitions from approximately 1 microm Kr clusters irradiated by high-intensity femtosecond laser pulses.

X-ray line emission from 2l-nl' transitions in Ne-like Kr and nearby ions has been observed from approximately 1 microm Kr clusters irradiated by fs-scale laser pulses at the JAERI facility in Kyoto, Japan. The incident laser intensity reached 10(19) W/cm2, with pulse energies from 50 to 300 mJ and pulse durations from 30 to 500 fs. The dependence of the x-ray spectral features and intensity on the incident laser intensity is rather weak, indicating that the 1-2 ps cluster lifetimes limit the number of ions beyond Ne-like Kr that can be produced by collisional ionization. Lines from F- to Al-like Kr emitted from the cluster plasmas have been identified using data from the relativistic multiconfiguration flexible atomic code. A collisional-radiative model based on these data has been constructed and used to determine that the cluster plasma has electron densities near 10(22) cm(-3), temperatures of a few hundred eV, and hot electron fractions of a few percent.

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PubMed2004

Analysis of high- n dielectronic Rydberg satellites in the spectra of Na -like Zn XX and Mg -like Zn XIX.

We have observed spectra from highly charged zinc ions in a variety of laser-produced plasmas. Spectral features that are Na - and Mg -like satellites to high- n Rydberg transitions in the Ne -like Zn XXI spectrum are analyzed and modeled. Identifications and analysis are made by comparison with highly accurate atomic structure calculations and steady state collisional-radiative models. Each observed Zn XX and Zn XIX feature comprises up to approximately 2 dozen individual transitions, these transitions are excited principally by dielectronic recombination through autoionizing levels in Na - and Mg -like Zn19+ and Zn18+. We find these satellites to be ubiquitous in laser-produced plasmas formed by lasers with pulse lengths that span four orders of magnitude, from 1 ps to approximately 10 ns. The diagnostic potential of these Rydberg satellite lines is demonstrated.

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PubMed2004

Charge-state distribution and Doppler effect in an expanding photoionized plasma.

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 xi=20-25 erg cm s(-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.

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PubMed2004

Efficient multi-keV X-ray sources from Ti-doped aerogel targets.

We have measured the production of hnu approximately 4.7 keV x rays from low-density Ti-doped aerogel (rho approximately 3 mg/cc) targets at the OMEGA laser facility (University of Rochester), with the goal of maximizing x-ray output. Forty OMEGA beams (lambda(L)=0.351 microm) illuminated the two cylindrical faces of the target with a total power that ranged from 7 to 14 TW. The laser fully ionizes the target (n(e)/n(crit)</=0.1), and a laser-bleaching wave excites, supersonically, the high-Z emitter ions in the sample. Ti K-shell x-ray emission was spectrally resolved with a two-channel crystal spectrometer and also with a set of filtered aluminum x-ray diodes; both instruments provide absolute measurement of the multi-keV x-ray emission. We find between 40 and 260 J of output with 4.67</=hnu</=5.0 keV.

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PubMed2004

Model for computing superconfiguration temperatures in nonlocal-thermodynamic-equilibrium hot plasmas.

A model is presented where the level-population densities in quasi-steady-state hot dense plasmas are described by means of large nonrelativistic superconfigurations (SC's), whose configuration populations follow a decreasing-exponential law versus energy (Boltzmann like) for a temperature depending on the SC. Two systems of linear equations are obtained. The first one yields the average-state population densities of the SC's. Using these results, the second system yields the SC temperatures. In this model, a very large number of atomic levels is accounted for in a simple way, thus yielding the configuration populations and, hence, the ionic distribution and average charge. It also yields accurate simulations of the spectra, which are of the essence for emissivity and absorption calculations. It opens a way to time-dependent calculations.

Kinetics↗

PubMed2003

X-ray spectral measurements and collisional radiative modeling of Ni- to Kr-like Au ions in electron beam ion trap plasmas.

The line emission of n=7-->3, 6-->3, 5-->3, and 4-->3 transitions in Ni- to Kr-like gold ions produced in the Livermore electron beam ion traps EBIT-I and EBIT-II has been recorded with an x-ray crystal spectrometer and a photometrically calibrated microcalorimeter. The plasmas had either monoenergetic electron beams with E(beam)=2.66, 3.53, or 4.54 keV or an experimentally simulated thermal electron distributions with T(e)=2.5 keV. The electron densities were approximately 10(12)cm(-3). The measured spectra have been compared to atomic structure calculations and synthetic spectra provided by the Hebrew University Lawrence Livermore Atomic Code atomic data package. Line identifications and accurate photon energy measurements have been made for many collisionally excited transitions. Approximately 140 lines have been identified in nine charge states. Agreement within 20-30 % exists between the measured and modeled line intensities for most lines excited by the monoenergetic electron beam plasmas, although some larger discrepancies can be found for some weaker features.

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PubMed2003

Determination of the charge state distribution of a highly ionized coronal Au plasma.

We present the first definitive measurement of the charge state distribution of a highly ionized gold plasma in coronal equilibrium. The experiment utilized the Livermore electron beam ion trap EBIT-II in a novel configuration to create a plasma with a Maxwellian temperature of 2.5 keV. The charge balance in the plasma was inferred from spectral line emission measurements which accounted for charge exchange effects. The measured average ionization state was 46.8+/-0.75. This differs from the predictions of two modeling codes by up to four charge states.

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PubMed2003

Advanced spectroscopic analysis of 0.8-1.0-MA Mo x pinches and the influence of plasma electron beams on L-shell spectra of Mo ions.

This paper presents a detailed investigation of the temporal, spatial, and spectroscopic properties of L-shell radiation from 0.8 to 1.0 MA Mo x pinches. Time-resolved measurements of x-ray radiation and both time-gated and time-integrated spectra and pinhole images are presented and analyzed. High-current x pinches are found to have complex spatial and temporal structures. A collisional-radiative kinetic model has been developed and used to interpret L-shell Mo spectra. The model includes the ground state of every ionization stage of Mo and detailed structure for the O-, F-, Ne-, Na-, and Mg-like ionization stages. Hot electron beams generated by current-carrying electrons in the x pinch are modeled by a non-Maxwellian electron distribution function and have significant influence on L-shell spectra. The results of 20 Mo x-pinch shots with wire diameters from 24 to 62 microm have been modeled. Overall, the modeled spectra fit the experimental spectra well and indicate for time-integrated spectra electron densities between 2 x 10(21) and 2 x 10(22) cm(-3), electron temperatures between 700 and 850 eV, and hot electron fractions between 3% and 7%. Time-gated spectra exhibit wide variations in temperature and density of plasma hot spots during the same discharge.

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PubMed2003

Influence of optical thickness and hot electrons on Rydberg spectra of Ne-like and F-like copper ions.

Spectra in the 7.10 to 8.60 A range from highly charged copper ions are observed from three different laser-produced plasmas (LPPs). The LPPs are formed by a 15-ns Nd:glass laser pulse (type I: E(pulse)=1-8 J, lambda=1.064 microm), a 1-ps Nd:glass laser pulse (type II: E(pulse)=1 J, lambda=1.055 microm), and a 60-fs Ti:sapphire laser pulse (type III: E(pulse)=800 mJ, lambda=790 nm). The spectra of high-n (n<or=14) transitions in highly charged copper ions, Cu19+ to Cu21+, are recorded with a high energy resolution (lambda/deltalambda=3000-8000) spectrometer using a spherically bent mica or quartz crystal. Collisional-radiative models are computed for the emission from each plasma. The sensitivity of the model spectra to opacity effects and to populations of superthermal electrons is studied. For the type I LPPs, opacity effects, treated with escape factors, are necessary to get the correct relative intensities of high-n (n=5, 6) Ne-like Cu19+ emission features. In the case of the type II LPPs, the contrast between the laser prepulse and the main pulse has been varied from low, I(main)/I(pp)=7 x 10(4), to high, I(main)/I(pp)=3.8 x 10(7). For plasmas from low contrast shots, we find good agreement between the observed spectra and optically thin simulations with bulk electron temperatures T(bulk)=0.4 keV and a small population of superthermal electrons (T(hot)=5.0 keV) that is f(hot)<or=10(-5) of the bulk electron population. For high-contrast type II LPPs, we find higher densities and a combination of f(hot) approximately 10(-5) and escape factors best describes the data. For the type III 60-fs LPPs, a population of superthermal electrons (T(hot) approximately 5 keV) that is approximately 5 x 10(-5) of the bulk electron population (T(bulk) approximately 0.2 keV) is required to reproduce the observed spectra. The effect of both escape factors and hot electrons in the CR models is to increase the ionization balance and dramatically increase the number of strong lines for each ion considered. We have studied both opacity effects and hot-electron influence on high-n transitions of highly charged Ne-, F-, and O-like ions.

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PubMed2002

Time-resolved plasma spectroscopy of thin foils heated by a relativistic-intensity short-pulse laser.

Time-resolved K-shell x-ray spectra are recorded from sub-100 nm aluminum foils irradiated by 150-fs laser pulses at relativistic intensities of Ilambda(2)=2 x 10(18) W microm(2)/cm(2). The thermal penetration depth is greater than the foil thickness in these targets so that uniform heating takes place at constant density before hydrodynamic motion occurs. The high-contrast, high-intensity laser pulse, broad spectral band, and short time resolution utilized in this experiment permit a simplified interpretation of the dynamical evolution of the radiating matter. The observed spectrum displays two distinct phases. At early time, < or =500 fs after detecting target emission, a broad quasicontinuous spectral feature with strong satellite emission from multiply excited levels is seen. At a later time, the He-like resonance line emission is dominant. The time-integrated data is in accord with previous studies with time resolution greater than 1 ps. The early time satellite emission is shown to be a signature of an initial large area, high density, low-temperature plasma created in the foil by fast electrons accelerated by the intense radiation field in the laser spot. We conclude that, because of this early time phenomenon and contrary to previous predictions, a short, high-intensity laser pulse incident on a thin foil does not create a uniform hot and dense plasma. The heating mechanism has been studied as a function of foil thickness, laser pulse length, and intensity. In addition, the spectra are found to be in broad agreement with a hydrodynamic expansion code postprocessed by a collisional-radiative model based on superconfiguration average rates and on the unresolved transition array formalism.

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PubMed2002

Spectroscopy of heliumlike argon resonance and satellite lines for plasma temperature diagnostics.

The n=2-1 spectral emission pattern of heliumlike argon, together with the associated satellite emission originating from lithiumlike argon have been measured with high-resolution x-ray spectroscopy at the Berlin electron-beam ion trap. The observed line intensity across a wide range of excitation energies was weighted by an electron-energy distribution to analyze as a function of plasma temperature the line ratios between KLL dielectronic recombination satellites, in particular the j+z, j, and k satellites, and the w-resonance line. A good agreement between various theoretical models is found, supporting the method of line-ratio measurement as a temperature diagnostic for plasmas. A value for the so-called R-line ratio is determined and calculations with the HULLAC suite of codes predict it to be electron density independent over a wide range.

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PubMed2002

Heating of thin foils with a relativistic-intensity short-pulse laser.

K-shell x-ray spectroscopy of sub-100 nm Al foils irradiated by high contrast, spatially uniform, 150 fs, Ilambda (2)=2 x 10(18) W microm(2)/cm(2), laser pulses is obtained with 500 fs time resolution. Two distinct phases occur: At </=500 fs a broad feature comparable to the resonance transitions occurs due to satellites, and at >/=500 fs the resonance transitions dominate. Initial satellites arise from a large area, high density, low temperature (approximately 100 eV) plasma created by fast electrons. Thus, contrary to predictions, a short, high intensity laser incident on a thin foil does not create a uniform, hot dense plasma.

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PubMed2002

Hot-electron influence on L-shell spectra of multicharged Kr ions generated in clusters irradiated by femtosecond laser pulses.

Strong L-shell x-ray emission has been obtained from Kr clusters formed in gas jets and irradiated by 60-500-fs laser pulses. Spectral lines from the F-, Ne- Na-, and Mg-like charge states of Kr have been identified from highly resolved x-ray spectra. Spectral line intensities are used in conjunction with a detailed time-dependent collisional-radiative model to diagnose the electron distribution functions of plasmas formed in various gas jet nozzles with various laser pulse durations. It is shown that L-shell spectra formed by relatively long nanosecond-laser pulses can be well described by a steady-state model without hot electrons when opacity effects are included. In contrast, adequate modeling of L-shell spectra from highly transient and inhomogeneous femtosecond-laser plasmas requires including the influence of hot electrons. It is shown that femtosecond-laser interaction with gas jets from conical nozzles produces plasmas with higher ionization balances than plasmas formed by gas jets from Laval nozzles, in agreement with previous work for femtosecond laser interaction with Ar clusters.

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PubMed2002

Soft-x-ray spectra of highly charged Kr ions in an electron beam ion trap.

Systematic variation of the electron-beam energy in the EBIT-II electron beam ion trap has been employed to produce soft-x-ray spectra (20-75 A) of Kr with well-defined maximum charge states ranging from Cu- to Al-like ions. Guided by large-scale relativistic atomic structure calculations, the strongest lines have been identified with Delta n=1 (n=3 to n(')=4) transitions from Ni- to P-like ions (Kr(8+)-Kr(21+)), as well as a number of 3p-4d and 3d-5f transitions.

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PubMed2001

Observations of the vacuum ultraviolet and x-ray brightness profiles of Fe, Ni, and Ge in magnetically confined fusion plasmas.

The spatial brightness profiles of emission lines for the K-like through He-like ionization states of Fe, Ge, and Ni have been measured during a set of experiments in which Fe and Ge were introduced into FTU tokamak plasmas by using the laser blowoff technique. Nickel was an intrinsic impurity observed during these experiments that was sputtered from the inconel limiter. The brightness profiles were measured by spatially scanable, photometrically calibrated vaccum ultraviolet and x-ray spectrometers that covered the 1 to 1700 A region. Simulations of these profiles and the time evolution of the laser blowoffs were performed with the MIST transport code using several sets of atomic physics compilations [ADPAK (originally in MIST), Arnaud and Raymond (AR92), Arnaud and Rothenflug (AR85), Mazzotta et al., and Mattioli (an extension to Mazzotta)]. The goal was to determine which set of available rates could best simulate the measured spatial brightness profiles and the charge state balance in the plasma. The Mazzotta et al. (for Fe and Ni), the Mattioli (for Ge), and the AR92 (for Fe only) rates adequately simulated the He-, Li-, Be-, Na-, Mg-like ionization states. The F- to B-like charge states could not be simulated by these compilations unless the relevant dielectronic rates were multiplied by a factor of 2. The ADPAK rates could not adequately predict any of the charge states of Fe, Ge, or Ni.

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PubMed2001

Ionization balance in inertial confinement fusion hohlraums.

We present the first x-ray spectroscopic measurements of the ionization balance in inertial confinement fusion hohlraums supported by 4omega 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 slightly shifted indicating nonsteady state kinetics.

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PubMed1999

Experimental and simulated neon spectra in the 10-nm wavelength region from tokamak and reversed field pinch plasmas.

Experimental neon spectra (in the 10-nm region), from the tokamak Tore Supra and the reversed field pinch experiment RFX, have been simulated. The spectra include lines from three neon ionization states, namely Ne(7+), Ne(6+), and Ne(5+) ions. Collisional radiative models have been built for these three Ne ions, considering electron collisional excitation and radiative decay as populating processes of the excited states. These models give photon emission coefficients for the emitted lines at electron density and temperature values corresponding to the experimental situations. Impurity modelling is performed using a one-dimensional impurity transport code, calculating the steady-state radial distribution of the Ne ions. The Ne line brightnesses are evaluated in a post-process subroutine and simulated spectra are obtained. The parts of the spectra corresponding to a single ionization state do not depend on the experimental conditions and show good agreement with the simulated single ionization state spectra. On the other hand, the superposition of the three spectra depends on the experimental conditions, as a consequence of the fact that the ion charge distribution depends not only on the radial profiles of the electron density and temperature, but also of the impurity transport coefficients. Simulations of the Ne spectra (including transport) give confidence in the atomic physics calculations; moreover, they allow the determination of the transport coefficients in the plasma region emitting the considered ionization states.

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