Robert F Heeter

Robert F Heeter
Lawrence Livermore National Laboratory | LLNL · Physics Division

Ph.D.

About

132
Publications
6,317
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
2,046
Citations
Citations since 2016
6 Research Items
737 Citations
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
Additional affiliations
June 1999 - present
Lawrence Livermore National Laboratory
Position
  • Physicist
Description
  • X-Ray Spectroscopy of High-Energy-Density Plasmas Coordinator for LLNL Experiments at the Omega Laser Facility
August 1993 - June 1999
Princeton University
Position
  • PhD Student
Description
  • Magneto-hydrodynamic spectroscopy of tokamak plasmas NSF Fellowship. Hertz Fellowship.

Publications

Publications (132)
Article
Full-text available
Accurate models for opacity of partially ionized atoms are important for modeling and understanding stellar interiors and other high-energy-density phenomena such as inertial confinement fusion. Lawrence Livermore National Laboratory is leading a multilaboratory effort to conduct experiments on the National Ignition Facility (NIF) to try to reprodu...
Article
Full-text available
Direct drive implosions of plastic capsules have been performed at the National Ignition Facility to provide a broad-spectrum (500–2000 eV) X-ray continuum source for X-ray transmission spectroscopy. The source was developed for the high-temperature plasma opacity experimental platform. Initial experiments using 2.0 mm diameter polyalpha-methyl sty...
Article
X-ray opacity is a crucial factor of all radiation-hydrodynamics calculations, yet it is one of the least validated of the material properties in the simulation codes. Recent opacity experiments at the Sandia Z-machine have shown up to factors of two discrepancies between theory and experiment, casting doubt on the validity of the opacity models. T...
Article
Accurate models of X-ray absorption and re-emission in partly stripped ions are necessary to calculate the structure of stars, the performance of hohlraums for inertial confinement fusion and many other systems in high-energy-density plasma physics. Despite theoretical progress, a persistent discrepancy exists with recent experiments at the Sandia...
Article
Recent experiments at the Sandia National Laboratory Z facility have called into question models used in calculating opacity, of importance for modeling stellar interiors. An effort is being made to reproduce these results at the National Ignition Facility (NIF). These experiments require a new X-ray opacity spectrometer (OpSpec) spanning 540 eV–21...
Article
This paper presents experimental scalings of the electrons and positrons produced by intense laser-target interactions at relativistic laser intensities (1018–1020 W cm−2). The data were acquired from three short-pulse laser facilities with laser energies ranging from 80 to 1500 J. We found a non-linear (≈EL 2) scaling of positron yield [Chen et al...
Article
Full-text available
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...
Article
Filtered x-ray diode (XRD) arrays are often used to measure x-ray spectra vs. time from spectrally continuous x-ray sources such as hohlraums. A priori models of the incident x-ray spectrum enable a more accurate unfolding of the x-ray flux as compared to the standard technique of modifying a thermal Planckian with spectral peaks or dips at the res...
Conference Paper
The National Ignition Facility (NIF) Opacity Spectrometer (OpSpec) is a modular spectrometer designed initially for opacity experiments on NIF. The design of the OpSpec is presented in light of the requirements and constraints. Potential dispersing elements and detector configurations are presented, and the advantages and disadvantages of each conf...
Article
Full-text available
For over fifteen years astronomers at the University of Maryland and theorists and experimentalists at LLNL have investigated the origin and dynamics of the famous Pillars of the Eagle Nebula, and similar parsec-scale structures at the boundaries of HII regions in molecular hydrogen clouds. Eagle Nebula was selected as one of the National Ignition...
Article
A multipurpose spectrometer (MSPEC) with elliptical crystals is in routine use to obtain x-ray spectra from laser produced plasmas in the energy range 1.0-9.0 keV. Knowledge of the energy-dependent response of the spectrometer is required for an accurate comparison of the intensities of x-ray lines of different energy. The energy-dependent response...
Article
Full-text available
Collimation of positrons produced by laser-solid interactions has been observed using an externally applied axial magnetic field. The collimation leads to a narrow divergence positron beam, with an equivalent full width at half maximum beam divergence angle of 4􏰂 vs the un-collimated divergence of about 20􏰂. A fraction of the laser-produced relativ...
Article
Progress toward ignition at the National Ignition Facility (NIF) has been focused on furthering the understanding of implosion performance. Implosion performance depends on the capsule fuel shape, on higher mode asymmetries that may cause hydrodynamic instabilities to quench ignition, on time-dependent asymmetries introduced by the hohlraum target,...
Article
Full-text available
Experiments conducted at the National Ignition Facility using shaped laser pulses with more than 1 MJ of energy have demonstrated the ability to control the implosion symmetry under ignition conditions. To achieve thermonuclear ignition, the low mode asymmetries must be small to minimize the size of the hotspot. The symmetry tuning experiments use...
Article
Full-text available
We have carried out precision optimization of inertial confinement fusion ignition scale implosions. We have achieved hohlraum temperatures in excess of the 300 eV ignition goal with hot-spot symmetry and shock timing near ignition specs. Using slower rise pulses to peak power and extended pulses resulted in lower hot-spot adiabat and higher main f...
Article
Full-text available
Measurements have been made of the in-flight dynamics of imploding capsules indirectly driven by laser energies of 1–1.7 MJ at the National Ignition Facility [Miller et al., Nucl. Fusion 44, 228 (2004)]. These experiments were part of the National Ignition Campaign [Landen et al., Phys. Plasmas 18, 051002 (2011)] to iteratively optimize the inputs...
Article
We present evidence that electromagnetic crosstalk between independent strips in gated x-ray framing cameras can affect relative gains by up to an order of magnitude and gate arrival times up to tens of picoseconds when strip separation times are less then ∼1 ns. Crosstalk is observed by multiple methods, and it is confirmed by direct measurements...
Article
The Eagle Nebula NIF experiment was one of nine selected for laser time through the Science on NIF program. The goal of this scale laboratory experiment is to study the dynamic evolution of distinctive structures in star forming regions of astrophysical molecular clouds such as the Pillars of the Eagle Nebula. That evolution is driven by photoioniz...
Article
Photoionized plasmas are present in many astrophysical environments, such as accretion disks and radiatively-driven winds of x-ray binaries and active galactic nuclei. We discuss an experimental and modeling effort in which the intense x-ray flux emitted at the collapse of a z-pinch is employed to produce and backlight a neon photoionized plasma to...
Article
Full-text available
Thin-shell deuterium-helium-3 (DHe3) filled glass capsules on the Omega laser provide a fast-implosion experimental platform for developing separate time-resolved measurements of ion, electron, and radiation temperatures in nonequilibrium plasmas. Dynamically significant non-local thermodynamic equilibrium (NLTE) conditions are created by the addit...
Article
Non-burning thermonuclear fuel implosion experiments have been fielded on the National Ignition Facility to assess progress toward ignition by indirect drive inertial confinement fusion. These experiments use cryogenic fuel ice layers, consisting of mixtures of tritium and deuterium with large amounts of hydrogen to control the neutron yield and to...
Article
V. GLEBOV, P. RADHA, T. SANGSTER, LLE, R. OLSON, R. LEEPER, SNL, J. KLINE, G. KYRALA, D. WILSON, LANL, J. KILKENNY, A. NIKROO, GA, C. SANGSTER, LLE The Wedge Range Filter (WRF) proton spectrometer was developed for OMEGA and transferred to the NIF as a National Ignition Campaign (NIC) diagnostic. In tuning campaign implosions containing D and ^3He...
Article
We present methods and results for off-line testing of gated x-ray framing cameras such as the GXDs in use at the National Ignition Facility (NIF). These cameras capture a time dependent sequence of images by sending a voltage pulse across a stripline-coated microchannelplate(mcp). The amplification mechanism of the mcp produces a time-dependent ga...
Conference Paper
X-ray imaging is integral to the measurement of the properties of hot plasmas. To this end, a suite of gated x-ray imagers have been developed for use in a wide range of experiments at the National Ignition Facility (NIF). These instruments are sensitive to x-rays over the range of 0.7-90keV and can acquire images at 20ps intervals for source inten...
Article
We present a modeling study of time-dependent atomic kinetics for a neon photoionized plasma. The neon atomic model considers several ionization stages of highly-charged neon ions as well as a detailed structure of non-autoionizing and autoionizing energy levels in each ion. Atomic processes populating and de-populating the energy levels consider p...
Article
We discuss a series of experiments performed at the Z facility in which photoionized plasmas were produced by driving a neon-filled gas cell with the intense x-ray flux emitted at the collapse of a z-pinch. The broad-band radiation flux from the z-pinch is used to both create the neon photoionised plasma and provide a source of backlighting photons...
Article
Assessing the ablator performance around the time of peak implosion velocity is an important step towards achieving ignition. Using x-ray radiography the time-resolved velocity, mass, and areal density of the remaining unablated shell were measured near peak velocity on NIF implosions. With the simple rocket model this allowed the ablation pressure...
Article
We report calculations of energy levels, radiative rates and electron impact excitation rates for transitions in H-like N VII, O VIII, F IX, Ne X and Na XI. The general-purpose relativistic atomic structure package (grasp) is adopted for calculating energy levels and radiative rates, while the Dirac atomic R-matrix code (darc) and the flexible atom...
Article
In this paper, we report calculations of energy levels, radiative rates and electron impact excitation rates for transitions in Li-like N V, F VII, Ne VIII and Na IX. The general-purpose relativistic atomic structure package (GRASP) is adopted for calculating energy levels and radiative rates, while for determining the collision strengths and subse...
Article
X-ray transmission spectra from fully characterized, high temperature plasmas provide validation benchmarks for high-energy-density physics models of interest to stellar astrophysics. This work presents new data from experiments at the Omega laser. 24 beams (at 500J/beam) heat the outer chambers of a 3-part (shine-shielded), 1.6 mm diameter hohlrau...
Article
Energy levels and radiative rates for E1, E2, M1, and M2 transitions among the lowest 49 levels, belonging to the 1s2, 1s2ell, 1s3ell, 1s4ell, and 1s5ell configurations of F VIII, are reported here for which the GRASP code has been adopted. Collision strengths have also been calculated, up to an energy of 150 Ryd, using the fully relativistic DARC...
Article
In this paper, we report calculations for energy levels, radiative rates and electron impact excitation rates for transitions in He-like N VI, F VIII and Na X. The general-purpose relativistic atomic structure package (grasp) is adopted for calculating energy levels and radiative rates, and for determining the collision strengths and subsequently t...
Article
Full-text available
Photoionised plasmas are common in astrophysical environments and new high resolution spectra from such sources have been recorded in recent years by the Chandra and XMM-Newton satellites. These provide a wealth of spectroscopic information and have motivated recent efforts aimed at obtaining a detailed understanding of the atomic-kinetic and radia...
Article
A novel time, space, and energy-resolved x-ray spectrometer has been developed which produces, in a single snapshot, a broadband and relatively calibrated spectrum of the x-ray emission from a high-energy density laboratory plasma. The opacity zipper spectrometer (OZSPEC-1) records a nearly continuous spectrum for x-ray energies from 240 to 5800 eV...
Article
Full-text available
The Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory is being used to absolutely calibrate the transmission efficiency of x-ray filters employed by diodes and spectrometers used to diagnose laser-produced plasmas. EBIT emits strong, discrete monoenergetic lines at appropriately chosen x-ray energies. X rays are d...
Article
Photoionised plasmas are common in astrophysical environments. New high resolution spectra from such sources have been recorded in recent years by the Chandra and XMM-Newton satellites. These provide a wealth of spectroscopic information and have motivated recent efforts aimed at obtaining a detailed understanding of the atomic-kinetic and radiativ...
Article
The first demonstration of laser driven dynamic Hohlraums (LDDH) as a spectrally smooth backlighter source for opacity and temperature measurements through absorption spectrometry of materials in local thermodynamic equilibrium at temperatures >150 eV has been made. This is a crucial temperature regime for future astrophysics and ignition fusion ex...
Article
Full-text available
We present a series of benchmark measurements of the ionization balance of well-characterized gold plasmas with and without external radiation fields at electron densities near 10{21} cm{-3} and electron temperatures spanning the range 0.8 to 2.4 keV. We have analyzed time- and space-resolved M-shell gold emission spectra using a sophisticated coll...
Article
X-ray transmission opacity measurements provide a stringent test of the modeling of partly-stripped ions in high-temperature plasmas. While good agreement has been reached in studies of n=1 to n=2 (K-shell) and n=2 to n=3 (L-shell) absorption spectra, there remain significant differences between various models' predictions of the n=3 to n=4 (M-band...
Article
We have performed experiments at the Omega Laser Facility to measure time-resolved electron (Te) and ion temperature (Ti) in implosion plasmas. These experiments used direct laser drive on thin glass shells filled with a mixture of D, ^3He, Kr, and Xe, and used neutron and proton emission to diagnose Ti along with x-ray emission to diagnose Te. The...
Article
Full-text available
A first set of shock timing, laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics (HEDP). In parallel, a robust set of optical and X-ray spectrom...
Article
Full-text available
The authors present a series of benchmark measurements of the ionization balance of well characterized gold plasmas with and without external radiation fields at electron densities near 10²¹ cm³ and various electron temperatures spanning the range 0.8 to 2.4 keV. They have analyzed time- and space-resolved M-shell gold emission spectra using a soph...
Article
The radiation temperature achieved inside a hohlraum, a high-Z cylindrical cavity heated by high-power lasers, is limited by plasma filling of ablated wall material. Recent work [ Dewald et al., Phys. Rev. Lett. 95, 215004 (2005) ] tested radiation temperature limits in a simple on-axis laser-hohlraum geometry and validated an analytic plasma-fill...
Article
Full-text available
An experimental campaign to maximize radiation drive in small-scale hohlraums has been carried out at the National Ignition Facility (NIF) at the Lawerence Livermore National Laboratory (Livermore, CA, USA) and at the OMEGA laser at the Laboratory for Laser Energetics (Rochester, NY, USA). The small-scale hohlraums, laser energy, laser pulse, and d...
Article
We have performed experiments at the Omega laser to validate opacity codes and associated opacity tables. These experiments used dual-axis imaging spectroscopy of tamped Gd:Al co-mixed samples. The samples were heated inside large (4mm dia.) shielded 3-chamber hohlraums to 35-45eV. The sample expansion was measured radiographically and the sample t...
Article
The Multiconfiguration Dirac-Fock method is used to calculate the energies of the 407 lowest levels in Fe XXII. These results are cross-checked using a suite of codes which employ the configuration interaction method on the basis set of transformed radial orbitals with variable parameters, and takes into account relativistic corrections in the Brei...
Article
Energy levels and the corresponding transition probabilities as well as oscillator strengths and line strengths for allowed (E1) and forbidden (E2, M1) transitions among the lowest 407 levels of boron-like Fe XXII are presented. Calculations were performed using the multiconfigurational Dirac-Fock GRASP code. (4 data files).
Article
Full-text available
A first set of shock propagation, laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4 beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics.
Article
The spectroscopic investigation of high temperature laser produced plasmas in general, and x-ray opacity experiments in particular, often requires instruments with both a broad coverage of x-ray energies and high spectral, spatial, and temporal resolution. We analyze the design, model the response, and report the commissioning of a spectrometer usi...
Article
Deposition of maximum laser energy into a small, high-Z enclosure in a short laser pulse creates a hot environment. Such targets were recently included in an experimental campaign using the first four of the 192 beams of the National Ignition Facility [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technology 26, 755 (1994)], under construc...
Article
Some applications of gated x-ray imagers, pulsed x-ray spectroscopy, for example, benefit if image capture is simultaneous and gain is uniform over the frame. Simultaneity and uniformity are both improved when the voltage gate pulse propagation distance is as short as practical across the micro-channel-plate. This article describes a micro-channel-...
Article
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 under near steady-state conditions. A curve-of-growth analysis, which includes the eff...
Article
A platform for analysis of material properties under extreme conditions, where a sample is bathed in radiation with a high temperature, is under development. Depositing maximum laser energy into a small, high-Z enclosure produces this hot environment. Such targets were recently included in an experimental campaign using the first four of the 192 be...
Article
Full-text available
Energies of the 700 lowest levels in $\ion{Fe}{xx}$ have been obtained using the multiconfiguration Dirac-Fock method. Configuration interaction method on the basis set of transformed radial orbitals with variable parameters taking into account relativistic corrections in the Breit-Pauli approximation was used to crosscheck our presented results. T...
Article
Full-text available
Relativistic analogues of integrals are applied to the nonrelativistic R-matrix code to demonstrate the possibilities of the method. An expression for the relativistic analogue of the multipole integral is obtained. Energy levels and electron impact excitation cross sections for transitions in C2+, Fe22+ and W70+, calculated with different codes, a...
Article
Energy levels and the corresponding transition probabilities as well as oscillator strengths and line strengths for allowed (E1) and forbidden (E2, M1) transitions among the lowest 700 levels of nitrogen-like Fe XX are presented. Calculations were performed using the multiconfigurational Dirac-Fock GRASP code. (4 data files).
Article
Full-text available
In experiments at the high-power Z-facility at Sandia National Laboratory in Albuquerque, New Mexico, we have been able to produce a low density photoionized laboratory plasma of Fe mixed with NaF. The conditions in the experiment allow a meaningful comparison with X-ray emission from astrophysical sources. The charge state distributions of Fe, Na...
Article
An experimental campaign to study radiation drive in small-scale halfraums has been carried out at the OMEGA laser at the Laboratory for Laser Energetics (LLE) in Rochester, N.Y, and at the HELEN laser at the Atomic Weapons Establishment (AWE) in Aldermaston, U.K.. The ``hot hohlraums'' fill with plasma so quickly that, late in time, most of the la...
Article
Stimulated Raman Scattering (SRS) has been studied experimentally in high temperature plasmas. The study was performed using the Omega laser at the Laboratory for Laser Energetics (LLE) in Rochester. Approximately 10 TW of power is incident upon targets, distributed among three cones. The hot-halfraums fill with plasma so quickly that, late in time...
Article
We have performed a set of bench-mark experiments on cans at the Rutherford Appleton Laboratory. Copper cans were heated with a 400 J, 1 ps, pulse focused to a 5 mu m spot size. The can diameters varied from 250 mu m to 800 mu m with a 10 mu m wall thickness. Several measurements were performed to estimate the plasma scale-length, heating mechanism...
Article
The determination of the charge state distribution (CSD) of highly ionized gold in high-density plasmas ( ˜ 10^21 cm-3) is critical for ICF experiments. Predictive calculations of the CSD have produced widely varying results. Previous experiments on NOVA have had some success in guiding the models at 2 keV. Here, CSD's have been investigated in Hot...
Article
Understanding and predicting the behavior of high-Z non-LTE plasmas is important for developing indirect-drive inertial confinement fusion. Extending earlier work from the Nova laser, we present results from experiments using the Omega laser to study the ionization balance of gold as a function of electron and radiation temperature. In these experi...
Article
Full-text available
X-ray spectrometers using elliptically bent crystals have desirable properties for applications requiring broad spectral coverage, good spectral resolution, and minimized source broadening. Previous work used custom-positioned film or microchannel plate detectors. We find it is also useful and cost-effective to field elliptical crystals in existing...
Article
Measuring time and space-resolved spectra is important for understanding Hohlraum and Halfraum plasmas. Experiments at the OMEGA laser have used the Nova TSPEC which was not optimized for the OMEGA diagnostic space envelope or for the needed spectroscopic coverage and resolution. An improved multipurpose spectrometer snout, the MSPEC, has been cons...