Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session BO7: Measurements and Diagnostics in Inertial Confinement Fusion |
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Chair: Dan Casey, Lawrence Livermore National Laboratory Room: OCC B117-119 |
Monday, November 5, 2018 9:30AM - 9:42AM |
BO7.00001: Diagnosing the hot-spot electron temperature from x-ray continnum emission measurements on NIF and OMEGA implosions Michael J. MacDonald, Daniel B. Thorn, Andrew G. MacPhee, Benjamin Bachmann, Dave K. Bradley, Bernard Kozioziemski, Otto L. Landen, Sabrina R. Nagel, Marilyn B. Schneider, Rahul C. Shah, Raymond E. Bahr, Duc M. Cao, Timothy Filkins, Sean P. Regan, Chuck Sorce, Christian Stoeckl, Wolfgang R. Theobald, Joe D. Kilkenny The hot-spot electron temperature (Te) is a key metric in determining the performance of inertial confinement fusion (ICF) implosions. The Continuum Spectrometer (ConSpec) infers hot-spot Te from the slope of the x-ray continuum emission in the photon energy range of 20 to 30 keV, where ion velocity and opacity effects are negligible. Additionally, the ConSpec provides spatial resolution to resolve background x-ray sources from the hot-spot emission. We present initial x-ray spectra, from which we infer hot-spot Te for DT cryogenic implosions at both the National Ignition Facility (NIF) and the OMEGA laser facility. In the NIF experiments, we infer the hot-spot Te from the continuum emission and measure the emission spectra from the laser deposition region near the hohlraum wall (the gold bubble). For the OMEGA direct-drive implosions, we evaluate the effectiveness of spatially resolving the hot-spot emission in the time-integrated measurement from coronal plasma emission. |
Monday, November 5, 2018 9:42AM - 9:54AM |
BO7.00002: Inferring Hot-Spot Electron Temperature from X-Ray Continuum Emission Duc M Cao, Rahul C Shah, Sean P Regan, Reuben Epstein, Chuck Sorce, Wolfgang R. Theobald, P.B Radha, Valeri N Goncharov The measured burn-weighted hot-spot ion temperature (Ti) is used as a key implosion performance metric, but it can be biased by motional blurring. To avoid this effect, the inverse slope of the x‑ray continuum emission spectrum will be used instead to infer a hot-spot electron temperature (Te). At a chosen photon energy, this inferred Te is exactly equal to the emission-weighted harmonic mean of the hot-spot Te. Near 15-keV spectral energy, the emission weighting is closest to burn weighting. For OMEGA-scale implosions, however, simulations indicate that correlation is too poor between the inferred Te and burn-weighted Ti for Ti measurement surrogacy because of the non-equilibrium state between Te and Ti. The inferred Te will therefore be treated as an independent metric to constrain post-shot simulations. Absolute emission measurements will also be used to infer the amount of hot-spot mix. In contrast to previous methods,1,2 a non-equilibrium temperature state and the inclusion of a Te measurement will be assumed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. 1 R. Epstein et. al., Phys. Plasmas 22, 022707 (2015). 2 T. Ma et al., Phys. Rev. Lett. 111, 085004 (2013). |
Monday, November 5, 2018 9:54AM - 10:06AM |
BO7.00003: Inference of the electron temperature in ICF implosions from X-ray spectra Grigory Kagan, O.L. Landen, D. Svyatskiy, Peter Hakel, C.J. McDevitt, H. Sio, N.V. Kabadi, R.A. Simpson, M. Gatu Johnson, Johan Frenje, Richard David Petrasso, Rahul C Shah, Michael J Rosenberg, Reuben Epstein, Sean P Regan, Tirtha R Joshi, Thomas E Weber, Hans Rinderknecht, Daniel Thorn, Marilyn Beth Schneider, David K. Bradley, Joe Kilkenny Two main approaches to assessing the electron temperature in ICF implosions are now being considered, which are based on measuring, respectively, line emission from a high-Z dopant such as krypton [1] or spectral continuum of 15 to 30 keV from electrons scattering off the D and T ions [2,3]. However, both types of the X-ray emission are due to suprathermal free electrons, which likely deviate from Maxwellian. We present the first theoretical study of both the line and continuum X-ray spectra from the hot-spot accounting for this deviation. In particular, we show that inferring the electron temperature as if the emitting electrons are Maxwellian gives a lower value than the actual one [4]. References [1] H. Chen et al. Phys. Plasmas 24 (2017) 072715 [2] L. Jarrott, et al. Rev. Sci. Inst. 87 (2016) 11E534 [3] D. B. Thorn et al. Proc. SPIE 10390 (2017) 1039009 [4] G. Kagan et al. https://arxiv.org/abs/1710.01343 |
Monday, November 5, 2018 10:06AM - 10:18AM |
BO7.00004: Time-Resolved Measurements of the Hot Spot Density and Temperature on the National Ignition Facility Lan Gao, Brian F Kraus, K. Hill, M. Bitter, P. Efthimion, M. B. Schneider, C. Thomas, Robert L Kauffman, D. Thorn, A. G. MacPhee, D. Liedahl The electron density and temperature and their evolution in the hot spot of a Kr-doped, big-foot implosion target were measured for the first time using an absolutely calibrated, streaked, high-resolution x-ray spectrometer on the National Ignition Facility (NIF). Kr Heα and Heβ complexes near stagnation were recorded on a streak camera with a temporal resolution of ~30 ps, with signal levels provided by a simultaneous time-integrated measurement on the image plate. The electron density was inferred through stark-broadened line shapes and the temperature was derived from the relative intensities of dielectronic satellites. The measurements are compared with hydrodynamic simulations of the big-foot implosion, as well as collisional-radiative calculations for line intensities and shapes. |
Monday, November 5, 2018 10:18AM - 10:30AM |
BO7.00005: The new Pulse Dilation – Photomultiplier Tube for gamma reaction history measurements at the National Ignition Facility H. Geppert-Kleinrath, H. W. Herrmann, Y. H. Kim, A. B. Zylstra, K. Meaney, F. E. Lopez, B. J. Pederson, J. Carrera, H. Khater, C. J. Horsfield, M. S. Rubery, S. Gales, A. Leatherland, A. Meadowcroft, T. Hilsabeck, J. D. Kilkenny, R. M. Malone, J. D. Hares, A. K. L. Dymoke-Bradshaw, J. Milnes, C. McFee Gas Cherenkov Detectors (GCD) have been successfully in use in diagnostics like the Gamma Reaction History (GRH) at the National Ignition Facility (NIF) for several years. The Cherenkov process is inherently fast, but the temporal resolution has been limited to ~100ps by state-of-the-art photomultiplier tube (PMT) technology. The new Pulse Dilation – Photomultiplier Tube (PD-PMT) at NIF will allow for temporal resolutions comparable to that of the gas cell, or ~10ps. Enhanced resolution will contribute to the quest for ignition in a crucial way through high precision reaction history measurements and better constrained models. First measurements at NIF might reveal features in the burn history such as onset of alpha heating, shock reverberations, and burn truncation due to dynamically evolving failure modes. The PD-PMT is well characterized by test measurements performed at AWE. GCD-3 - a Gas Cherenkov Detector fielded in a Well-DIM at NIF - serves as a test bed for the PD-PMT. The lessons learned by fielding PD-PMT on GCD-3 will contribute to the design of the next generation Gas Cherenkov Detector. |
Monday, November 5, 2018 10:30AM - 10:42AM |
BO7.00006: Narrowband radiography of ICF implosions on the NIF using the Crystal Backlighter Imager Gareth N Hall, Christine M Krauland, Laura Berzak Hopkins, Nathaniel B Thompson, Justin G Buscho, Marion J Ayers, Edwin R Casco, Sabrina R Nagel, Arthur C Carpenter, Emily R Hurd, Matthew S Dayton, Kyle Engelhorn, Terance Joseph Hilsabeck, Perry Bell, David K. Bradley The Crystal Backlighter Imager (CBI) is a quasi-monochromatic, near-normal incidence, spherically-bent crystal imager at the NIF. Being narrowband (a few eV), this diagnostic mitigates self-emission from the capsule hotspot, allowing ICF capsule implosions to be radiographed significantly closer to stagnation than the previous broadband pinhole-based area-backlighter platform. CBI can now utilize the Single Line of Sight (SLOS1) camera, which couples pulse-dilation technology to a hybrid-CMOS detector to allow capturing of up to 4 rapidly gated (~50ps) frames. Using only a single crystal, CBI with SLOS is now capable of obtaining 4 high temporal and spatial resolution radiographs on a single NIF shot. Recently, CBI with SLOS produced 4 radiographs during the final ~300ps of an indirect-drive ICF implosion in which a high-density-carbon capsule with a tritium-hydrogen-deuterium ice layer was driven by a 1MJ laser pulse. Results from this experiment will be presented, together with efforts to increase the backlighter efficiency of the current 11.6keV CBI system and develop lower-energy CBI configurations. Release# LLNL-ABS-753490. |
Monday, November 5, 2018 10:42AM - 10:54AM |
BO7.00007: Selenium X-ray K-shell source optimization for the Crystal Backlighter Imager at the National Ignition Facility Christine M Krauland, Gareth N Hall, Gregory Elijah Kemp, Marilyn Beth Schneider, Daniel B. Thorn, Otto L Landen, David K. Bradley The Crystal Backlighter Imager (CBI) is a backlit quasi-monochromatic x-ray radiography system designed to image ICF implosions with the Se Heα line at 11.652 keV. This diagnostic has the capability to image late in an implosion because it only requires the source brightness to be larger than that of the capsule self-emission in a narrow bandwidth around the backlighter line energy. We present here a series of NIF experiments that aim to optimize the CBI configuration by increasing the number of Se Heα photons to the detector. Data will be shown from various backlighter target positions and laser configurations. Additionally, we will present NIF data from recent source development efforts to specifically improve laser to Se Heα x-ray conversion efficiency with a small (1 mm height, 1mm dia) Se-lined cylinder target. Larger cavity targets have shown an increase in temperature and emission from plasma stagnation on axis compared to open-geometry foils. Characterization and performance of the new source will be discussed and compared to the flat foil approach currently used with CBI. |
Monday, November 5, 2018 10:54AM - 11:06AM |
BO7.00008: A pseudo-Wolter microscope for core implosion imaging at the National Ignition Facility. Alexandre Do, Louisa Pickworth, Clément Trosseille, Jay Ayers, David K. Bradley, Perry Bell, Justin G Buscho, Joe Kilkenny, Philippe Troussel, Rene Wrobel, Daniel Soler, Pierre Santini Inertial confinement fusion experiments at the National Ignition Facility (NIF) use an X-ray drive to converge a ~1mm radius spherical shell ~30x its original radius. Typical core diameters range from 50 µm, in cryogenic layered implosions, to 100 µm in gas filled implosions. The x-ray emission is peaked between 8 and 10keV. Current X-ray imaging at NIF has a spatial resolution element around 10 µm which is insufficient to resolve structure the core. Low resolution and poor signal to noise ratio limits the observable features during the later stages of the implosion. Using grazing incidence toroidal mirrors in a pseudo-Wolter configuration, a focusing, 3-color, multi-channel x-ray microscope is in design for NIF. The system will have 15x magnification, a sub-5 µm full width at half maximum spatial resolution and a collection efficiency ~10-7 sr. It will be coupled to a state of the art single line of sight detector (SLOS) which has a temporal resolution ~50 ps. We will describe this pseudo-Wolter microscope whose high performances will give a time-resolved observation of the source shape features along with a plasma temperature and density measurements.Release # LLNL-ABS-753682. Prepared by LLNL under Contract DE-AC52-07NA27344 |
Monday, November 5, 2018 11:06AM - 11:18AM |
BO7.00009: The energy selected hot-spot X-ray emission image measurement in indirectly-driven implosions on SG-III facility by a multi-channel spatial flat-response KB microscope Xing Zhang, Yunsong Dong, Zhongjing Chen, Jianjun Dong, Feng Wang, Jianmin Yang, Shao'en Jiang, Yaran Li, Baozhong Mu The 2D hot spot X-ray emission image diagnostics, including the shape and the fine structure, are very important in the ICF implosions. Some advanced X-ray imaging systems with high spatial resolution and energy selection are required. The system with a multi-channel KB microscope and a gated X-ray detector has been developed on NIF and OMEGA. On SG-III facility, a 8-channel KB microscope was developed with the periodic multilayer mirrors. Due to the small grazing angle bandwidth, the reflectivity varied rapidly with the incident angle. The reflectivity flatness in the field-of-view (FOV) was poor. The measured image would be modulated with the spatial reflectivity response. Recently, a new 4-channel KB microscope with a spatial flat response was developed on SG-III facility. The Pt single-layer mirrors were adopted. A passing energy band of 5.7-7.1keV was obtained by the K-edge of a Fe filter. The FOV range was larger than 1mm. The variation of the reflectivity was less than 10% in a FOV range of 400μm and less than 20% in a range of 800μm. The estimated spatial resolution was about 5μm. The designed magnification was 21, and the covered solid angle was higher than 10-7 sr. The polar asymmetry of the hot spot X-ray emission was diagnosed in an equatorial view on SG-III facility. |
Monday, November 5, 2018 11:18AM - 11:30AM |
BO7.00010: Characterizing optical depth effects in cylindrical plasmas for density diagnostics in ICF plasmas Gabriel Perez-Callejo, Leonard C Jarrott, Edward V Marley, Duane A Liedahl, Robert F Heeter, Mark E Foord, Christopher W Mauche, Marilyn B Schneider, Justin S Wark Temperature and density diagnostics are critical for understanding laser coupling to high-Z hohlraums in ICF experiments at the National Ignition Facility. Over the past few years, there has been an effort to develop accurate diagnostic methods using x-ray spectroscopy of dot targets placed inside the hohlraum. The cylindrical geometry of these dots causes the intensity of the optically thick lines to have a non-trivial angular dependence. The degree of anisotropy is a function of the aspect ratio (H/R) of the dots and can provide information about their geometry (including their density). The OpticalDepth campaign at OMEGA laser aims for a better characterization of this effect. To keep the system as simple as possible, we have developed a platform to create a uniform cylindrical plasma by using microdots of a mid-Z material in order to use K-shell x-ray spectroscopy. The OMEGA target chamber configuration allows us to obtain spectra and images of the plasma expansion in the axial and radial directions. The simulations present good agreement with data, showing the potential capabilities of this method as a density diagnostic. |
Monday, November 5, 2018 11:30AM - 11:42AM |
BO7.00011: Characterizing and Synthesizing MMI Data Using 3D Geometrical Ray Tracing Dylan T Cliche, Roberto Claudio Mancini, Leslie Welser-Sherrill, Brian Michael Haines Inertial Confinement Fusion (ICF) is one method used to obtain controlled thermonuclear burn through either direct or indirect ablation of a millimeter-scale capsule with the use of high-power lasers. Although there have been large strides made in understanding the physics involved in order to create reliable physics models and codes, simulations and experiments still show discrepancies. A factor in this mismatch is the asymmetry of the implosions that occur experimentally. The multi-monochromatic X-ray imager (MMI) is an instrument which gives spatially, spectrally, and temporally resolved arrays of narrow-band x-ray images which can be used to extract temperature, density, and mixing spatial profiles. To understand the full potential and limitations of the instrument a three-dimensional geometrical ray tracing code has been created. By integrating the ray tracing code with an atomic and radiation transport model we can create the most accurate synthetic MMI data to date to compare experiment and simulation. Results are discussed obtained from the post-processing of implosion simulations produced with the radiation-hydrodynamics Rage code including inline the BHR mixing package. |
Monday, November 5, 2018 11:42AM - 11:54AM |
BO7.00012: Improving 3D density reconstruction in ICF fuel using synthetic neutron imaging data Verena Geppert-Kleinrath, Petr L Volegov, Carl Wilde, Aidan Crilly, Brian Appelbe The Los Alamos National Laboratory Advanced Imaging team is currently adding two additional lines-of-sight to the neutron imaging diagnostic at the National Ignition Facility. The additional views will deliver 3D shape information on the burning fusion fuel and allow for a more detailed understanding of asymmetries at stagnation. The recently deployed first phase - a passive energy-integrated imaging system on the north pole - provides a second view of the hot spot, allowing 3D density reconstruction of the fuel assembly from neutron images for the first time under certain symmetry assumptions. Since neutron images are inherently time-integrated, we study the effect of burn averaging on the density reconstruction using synthetic neutron imaging data produced with the Chimera rad-hydro code. A particular focus is placed on hotspot movement during burn time, as hypothesized previously through comparison of neutron imaging density with neutron activation diagnostics. |
Monday, November 5, 2018 11:54AM - 12:06PM |
BO7.00013: DT Yield and Ion Temperature Measurement with a Cherenkov Neutron Time-of-Flight Detector on OMEGA Vladimir Yu. Glebov, Chad J. Forrest, James P Knauer, Owen M Mannion, Sean P Regan, Thomas C Sangster, Christian Stoeckl, Mark J. Eckart, Gary Grim, Alastair Moore, David J. Schlossberg A Cherenkov neutron time-of-flight (nTOF) detector is currently installed in a collimated line of sight (LOS) on OMEGA at 13 m from the target next to a scintillator-based nTOF detector. The neutron-yield and ion-temperature measurements by these two detectors in the same LOS and at the same distance make it possible distinguish instrumental and physics effects in high-yield inertial confinement fusion experiments. The results of the measurements in experiments with cryogenic and room-temperature implosions with a wide range of neutron yields and ion temperatures will be presented. |
Monday, November 5, 2018 12:06PM - 12:18PM |
BO7.00014: The next-generation Magnetic Recoil Spectrometer for time-resolved measurement of the neutron spectrum at the National Ignition Facility (NIF) Johan Frenje, Cody E Parker, Maria Gatu Johnson, Brandon J Lahmann, Alexander Sandberg, Chikang Li, Fredrick Seguin, Richard David Petrasso, Terance Joseph Hilsabeck, Joseph David Kilkenny, Andy Mackinnon, Andrew G MacPhee The next-generation magnetic recoil spectrometer (MRSt) for time-resolved measurements of the neutron spectrum has been designed for the NIF. This spectrometer represents a paradigm shift in our thinking about neutron spectrometry for ICF applications, as it will provide simultaneously information about the burn history and time evolution of areal density, apparent ion temperature, yield and macroscopic flows during burn. From this type of data, an assessment of the evolution of hot-spot formation and fuel assembly can be made. According to simulations, the MRSt will provide accurate data with a time resolution of ∼20 ps and energy resolution of ∼200 keV for neutron yields above ∼1e16. At lower yields, the diagnostic will be operated at a higher-efficiency, lower-energy-resolution mode to provide a time resolution of ∼40 ps. As the discussed in this presentation, the key aspects of the MRSt functionality have also been experimentally demonstrated. The work was supported by DOE, LLNL and LLE. |
Monday, November 5, 2018 12:18PM - 12:30PM |
BO7.00015: Threshold for Measuring the Langdon Effect Using Collective Thomson Scattering Avram Milder, Robert Boni, Steven Ivancic, Joe Katz, Dustin H Froula The basis of many transport properties of a laser-produced plasma is contingent upon the understanding of the underlying electron distribution function. A method to infer the electron distribution function in a laser-produced plasma is proposed and applied to identifying flattopped electron distributions produced by inverse bremsstrahlung heating, known as the Langdon effect. The threshold to experimentally distinguish such distributions from Maxwellian is given. By angularly resolving Thomson spectrum over a range of angles, the threshold for identifying the electron distribution function can be reduced. A diagnostic to accomplish this is proposed using an f/3.3 by f/0.5 reflective collector, anamorphic relay, and spectrometer system that will simultaneously measure >100 angularly separated spectrum. |
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