Design of the opacity spectrometer for opacity measurements at the National Ignition Facility

Ross, P. W.; Heeter, R. F.; Ahmed, M. F.; Dodd, E. S.; Huffman, E.; Liedahl, D. A.; King, J. A.; Opachich, Y. P.; Schneider, M. B.; Perry, T. S.

doi:10.1063/1.4962819

Cited by 23 publications

(11 citation statements)

References 14 publications

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“…They have certainly deepened our understanding of the contributing absorption processes but have not yet resulted in definite missing opacities; in this respect, alternative experimental attempts to reproduce the larger-than-expected opacity measurements of [33] are currently in progress [101,102].…”

Section: Discussionmentioning

confidence: 99%

Computation of Atomic Astrophysical Opacities

Mendoza

2018

Atoms

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Abstract:The revision of the standard Los Alamos opacities in the 1980-1990s by a group from the Lawrence Livermore National Laboratory (OPAL) and the Opacity Project (OP) consortium was an early example of collaborative big-data science, leading to reliable data deliverables (atomic databases, monochromatic opacities, mean opacities, and radiative accelerations) widely used since then to solve a variety of important astrophysical problems. Nowadays the precision of the OPAL and OP opacities, and even of new tables (OPLIB) by Los Alamos, is a recurrent topic in a hot debate involving stringent comparisons between theory, laboratory experiments, and solar and stellar observations in sophisticated research fields: the standard solar model (SSM), helio and asteroseismology, non-LTE 3D hydrodynamic photospheric modeling, nuclear reaction rates, solar neutrino observations, computational atomic physics, and plasma experiments. In this context, an unexpected downward revision of the solar photospheric metal abundances in 2005 spoiled a very precise agreement between the helioseismic indicators (the radius of the convection zone boundary, the sound-speed profile, and helium surface abundance) and SSM benchmarks, which could be somehow reestablished with a substantial opacity increase. Recent laboratory measurements of the iron opacity in physical conditions similar to the boundary of the solar convection zone have indeed predicted significant increases (30-400%), although new systematic improvements and comparisons of the computed tables have not yet been able to reproduce them. We give an overview of this controversy, and within the OP approach, discuss some of the theoretical shortcomings that could be impairing a more complete and accurate opacity accounting.

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Section: Discussionmentioning

confidence: 99%

Computation of Atomic Astrophysical Opacities

Mendoza

2018

Atoms

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“…Details of the instrument design and engineering have been published separately (Ross et al 2015(Ross et al , 2016) but a few aspects of the design are worth mentioning since they extend the capability of NIF to perform opacity experiments. The axial orientation of the spectrometer is driven by the axially symmetric laser-target geometry on NIF.…”

Section: Instrumentation and Diagnosis Of Plasma Conditionsmentioning

confidence: 99%

Conceptual design of initial opacity experiments on the national ignition facility

et al. 2017

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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 Z facility studying iron in conditions characteristic of the solar radiative-convective transition region. The increased iron opacity measured at Z could help resolve a longstanding issue with the standard solar model, but requires a radical departure for opacity theory. To replicate the Z measurements, an opacity experiment has been designed for the National Facility (NIF). The design uses established techniques scaled to NIF. A laser-heated hohlraum will produce X-ray-heated uniform iron plasmas in local thermodynamic equilibrium (LTE) at temperatures 150 eV and electron densities 7 × 10 21 cm −3. The iron will be probed using continuum X-rays emitted in a ∼200 ps, ∼200 µm diameter source from a 2 mm diameter polystyrene (CH) capsule implosion. In this design, 2/3 of the NIF beams deliver 500 kJ to the ∼6 mm diameter hohlraum, and the remaining 1/3 directly drive the CH capsule with 200 kJ. Calculations indicate this capsule backlighter should outshine the iron sample, delivering a point-projection transmission opacity measurement to a time-integrated X-ray spectrometer viewing down the hohlraum axis. Preliminary experiments to develop the backlighter and hohlraum are underway, informing simulated measurements to guide the final design.

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“…The resulting backlighter and absorption spectra are projected into the NIF opacity spectrometer (OpSpec), an open-aperture time-integrated crystal spectrometer [12,13] pointed downward from the upper pole of the NIF target chamber. Inside OpSpec the X-rays propagate through three aluminized-plastic X-ray filters, Bragg-diffract off one of two convex rubidium acid phthalate (RbAP) crystals, then propagate past three more aluminized-plastic filters before being absorbed by one of two adjacent Fuji BAS-TR X-ray imaging plates [12,13]. After recent improvements [13] the spectrometer recently delivered the first analyzable transmission data [14].…”

Section: Introduction To the Nif Opacity Experimentsmentioning

confidence: 99%

“…The backlighter X-ray flash passes through a 750 × 1200-micron rectangular slot in a silicon-coppersilicon layered collimator, and then transits the hohlraum by passing either through or around the rectangular sample [3]. The resulting backlighter and absorption spectra are projected into the NIF opacity spectrometer (OpSpec), an open-aperture time-integrated crystal spectrometer [12,13] pointed downward from the upper pole of the NIF target chamber. Inside OpSpec the X-rays propagate through three aluminized-plastic X-ray filters, Bragg-diffract off one of two convex rubidium acid phthalate (RbAP) crystals, then propagate past three more aluminized-plastic filters before being absorbed by one of two adjacent Fuji BAS-TR X-ray imaging plates [12,13].…”

Section: Introduction To the Nif Opacity Experimentsmentioning

confidence: 99%

“…The X-ray transmission measurement itself is produced using point-projection X-ray spectroscopy as illustrated in Figure 1 (left), following previous design and implementation work [3,7]. Specific details of the opacity spectrometer (OpSpec) setup for shot N171214-001 are given below, but in brief the underlying symmetry of the experimental platform enables OpSpec to record two sets of spectra per shot, one per image plate, with each side of the spectrometer observing half of the sample in transmission, together with the backlighter spectrum passing around the sample on one side [3,12,13]. The two image plate detectors each record spectra from ~1000 to 2000 eV in one dimension, spatially resolving the spectra from the sample absorption (region U), backlighter (region V), sample self-emission (region E), and various instrument backgrounds in the other dimension.…”

Section: Introduction To the Measurements On Nif Shot N171214-001mentioning

confidence: 99%

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Iron X-ray Transmission at Temperature Near 150 eV Using the National Ignition Facility: First Measurements and Paths to Uncertainty Reduction

Heeter

Perry

Johns

et al. 2018

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Discrepancies exist between theoretical and experimental opacity data for iron, at temperatures 180-195 eV and electron densities near 3 × 10 22 /cm 3 , relevant to the solar radiative-convective boundary. Another discrepancy, between theory and helioseismic measurements of the boundary's location, would be ameliorated if the experimental opacity is correct. To address these issues, this paper details the first results from new experiments under development at the National Ignition Facility (NIF), using a different method to replicate the prior experimental conditions. In the NIF experiments, 64 laser beams indirectly heat a plastic-tamped rectangular iron-magnesium sample inside a gold cavity. Another 64 beams implode a spherical plastic shell to produce a continuum X-ray flash which backlights the hot sample. An X-ray spectrometer records the transmitted X-rays, the unattenuated X-rays passing around the sample, and the sample's self-emission. From these data, X-ray transmission spectra are inferred, showing Mg K-shell and Fe L-shell X-ray transitions from plasma at a temperature of~150 eV and electron density of~8 × 10 21 /cm 3 . These conditions are similar to prior Z measurements which agree better with theory. The NIF transmission data show statistical uncertainties of 2-10%, but various systematic uncertainties must be addressed before pursuing quantitative comparisons. The paths to reduction of the largest uncertainties are discussed. Once the uncertainty is reduced, future NIF experiments will probe higher temperatures (170-200 eV) to address the ongoing disagreement between theory and Z data.

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Design of the opacity spectrometer for opacity measurements at the National Ignition Facility

Cited by 23 publications

References 14 publications

Computation of Atomic Astrophysical Opacities

Computation of Atomic Astrophysical Opacities

Conceptual design of initial opacity experiments on the national ignition facility

Iron X-ray Transmission at Temperature Near 150 eV Using the National Ignition Facility: First Measurements and Paths to Uncertainty Reduction

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