Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session CO8: Neutron Diagnostics and Measurement Techniques/Direct Drive ICF |
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Chair: Patrick Knapp, Sandia National Laboratories Room: 203C |
Monday, October 23, 2017 2:00PM - 2:12PM |
CO8.00001: Upgraded Neutron Time-of-Flight Detectors for DT Cryogenic Implosions on OMEGA V.Yu. Glebov, C.J. Forrest, J.P. Knauer, O.M. Mannion, S.P. Regan, T.C. Sangster, C. Stoeckl The neutron time-of-flight (nTOF) system on the OMEGA laser was recently upgraded. Three new nTOF detectors of different designs were added to the existing detectors. There are now six nTOF detectors on OMEGA in the different lines of sight (LOS) to record the DT primary yield in $1\times 10^{12}$ to $1\times 10^{14}$ ranges and infer ion temperature above 2 keV. One new nTOF detector is located in a collimated LOS with a photomultiplier tube in a shielded location. For this nTOF detector it is possible to measure x-ray instrument response function, construct neutron response function, and calculate ion temperature by forward-fitting method. The ion-temperature fitting parameters for the other nTOF detectors located in the OMEGA Target Bay on an uncollimated LOS were adjusted to match the ion temperature against the nTOF detector in the collimated LOS on low-areal-density, warm target shots. All six nTOF detectors were calibrated by DT yield against a copper activation diagnostic on warm target shots. The design details, calibration results, and limitations of these OMEGA nTOF detectors will be presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 23, 2017 2:12PM - 2:24PM |
CO8.00002: Using Secondary Nuclear Reaction Products to Infer the Fuel Areal Density, Convergence, and Electron Temperatures of Imploding D$_{\mathrm{\mathbf{2\thinspace }}}$\textbf{and D}$^{\mathrm{\mathbf{3}}}$He Filled Capsules on the NIF B. Lahmann, J.A. Frenje, M. Gatu Johnson, F.H. Seguin, C.K. Li, R.D. Petrasso, E.P. Hartouni, C.B. Yeamans, H.G. Rinderknecht, D.B. Sayre, G. Grim, K. Baker, D.T. Casey, E. Dewald, C. Goyon, L.C. Jarrott, S. Khan, S. LePape, T. Ma, L. Pickworth, R. Shah, J.L. Kline, T. Perry, A. Zylstra, S.A. Yi In deuterium-filled inertial confinement fusion implosions, 0.82 MeV~$^{\mathrm{3}}$He and 1.01 MeV T (generated by the primary DD reaction branches) can undergo fusion reactions with the thermal deuterium plasma to create secondary D$^{\mathrm{3}}$He protons and DT neutrons, respectively. In regimes of moderate fuel areal density ($\rho $R~$\sim $~5 - 100 mg/cm$^{\mathrm{2}})$~the ratio of both of these secondary yields to the primary yield can be used to infer the fuel~$\rho $R, convergence ratio (CR), and an electron temperature (T$_{\mathrm{e}})$. This technique has been used on a myriad of deuterium filled capsule implosion experiments on the NIF using the neutron time of flight (nTOF) diagnostics to measure the yield of secondary DT neutrons and CR-39 based wedge range filters (WRFs) to measure the yield of secondary D$^{\mathrm{3}}$He protons. This work is supported in part by the U.S. DoE and LLNL. [Preview Abstract] |
Monday, October 23, 2017 2:24PM - 2:36PM |
CO8.00003: Indications of Bulk-Fluid Motion in Direct-Drive Implosions O.M. Mannion, K.S. Anderson, C.J. Forrest, V.Yu. Glebov, V.N. Goncharov, J.P. Knauer, P.B. Radha, S.P. Regan, T.C. Sangster, C. Stoeckl The neutron spectrum produced by a burning plasma encodes essential information about the fusion products and serves as an important diagnostic for inertial confinement fusion experiments. At the Omega Laser Facility, neutron time-of-flight measurements are used to interpret the first and second moment of the neutron spectrum. These moments have been shown to be directly related to properties of the plasma, such as bulk fluid motion and apparent ion temperature. New measurement devices allow for unprecedented accuracy in the measurement of these moments and will provide a better understanding of the performance of direct-drive implosions. We present measurements of the first moment of the DT and $\mbox{D}_{2} $ peaks in DT implosions and show that variations in the first moment indicate bulk fluid motion of the plasma. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 23, 2017 2:36PM - 2:48PM |
CO8.00004: A novel design for scintillator-based neutron and gamma imaging in inertial confinement fusion Verena Geppert-Kleinrath, Theresa Cutler, Chris Danly, Amanda Madden, Frank Merrill, Josh Tybo, Petr Volegov, Carl Wilde The LANL Advanced Imaging team has been providing reliable 2D neutron imaging of the burning fusion fuel at NIF for years, revealing possible multi-dimensional asymmetries in the fuel shape, and therefore calling for additional views. Adding a passive imaging system using image plate techniques along a new polar line of sight has recently demonstrated the merit of 3D neutron image reconstruction. Now, the team is in the process of designing a new active neutron imaging system for an additional equatorial view. The design will include a gamma imaging system as well, to allow for the imaging of carbon in the ablator of the NIF fuel capsules, constraining the burning fuel shape even further. The selection of ideal scintillator materials for a position-sensitive detector system is the key component for the new design. A comprehensive study of advanced scintillators has been carried out at the Los Alamos Neutron Science Center and the OMEGA Laser Facility in Rochester, NY. Neutron radiography using a fast-gated CCD camera system delivers measurements of resolution, light output and noise characteristics. The measured performance parameters inform the novel design, for which we conclude the feasibility of monolithic scintillators over pixelated counterparts. [Preview Abstract] |
Monday, October 23, 2017 2:48PM - 3:00PM |
CO8.00005: Proton Radiography experiments and 3D simulations of laser-driven hohlraums Paul-Edouard Masson-Laborde, S. laffite, C.K Li, S.C. Wilks, R. Riquier Proton radiography experiments of laser-irradiated hohlraums (with 3 MeV DD and 14.7 MeV D3He protons) performed at the Omega laser facility provide critical information on hohlraum environment: self-generated spontaneous electric and magnetic fields, plasma blow-off of the wall and hydrodynamic instabilities. Motion of the laser-driven plasma bubbles in gold and CH hohlraums under several different irradiation patterns have be analyzed by proton radiography. Comparisons with 3D hydrodynamic simulations in these different configurations coupled to a proton trajectography package will be presented. The 3D effect in plasma expansion, as well as the role and importance of electric field in the proton deflexion will be discussed by comparisons to experimental results. All these comparisons provide insight into important issues in inertial confinement fusion and hohlraum physics. [Preview Abstract] |
Monday, October 23, 2017 3:00PM - 3:12PM |
CO8.00006: Saturn Designs for Small Proton-Backlighter Targets at the National Ignition Facility R.S. Craxton, E.M. Garcia, L.T. Browning, S. Le Pape, H.-S. Park, C.K. Li, A.B. Zylstra Small exploding-pusher capsules with D$^{\mathrm{3}}$He fill are ideal sources for high-resolution proton radiography for many high-energy-density experiments at the National Ignition Facility (NIF). However, the laser energy that can be delivered to these capsules is currently limited by the need to minimize laser blowby---unabsorbed laser light passing by the target into opposing beam ports with the potential of damaging laser optics. This issue arises because it is logistically convenient to leave the indirect-drive phase plates in place. Saturn targets,\footnote{R. .S. Craxton and D.W. Jacobs-Perkins, Phys. Rev. Lett. \textbf{94}, 095002 (2005).} in which the capsule is surrounded by a toroidal plastic ring, promise to remove the energy limitation by blocking blowby light, permitting a brighter proton source. A design has been developed using the 2-D hydrodynamics code \textit{SAGE}\footnote{R. S. Craxton and R.L. McCrory, J. Appl. Phys. \textbf{56}, 108 (1984).} for a ring that can be used to block the laser blowby for target diameters from 440 to 866 $\mu $m and drive beams from any of the NIF quads. Full-power NIF beams can be safely used. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 23, 2017 3:12PM - 3:24PM |
CO8.00007: Proton deflectometry characterization of Biermann-Battery field advection Bradley Pollock, Alastair Moore, Nathan Meezan, Dave Eder, Jave Kane, David Strozzi, Scott Wilks, Hans Rinderknecht, Alex Zylstra, Shinsuke Fujioka, Gregory Kemp, John Moody Laser-foil interactions are well known to produce azimuthal magnetic fields around the laser spot due to the orthogonal density and temperature gradients that develop near the foil surface (the Biermann-Battery effect). Simulations show that these fields produced inside hohlraums used for indirect drive experiments at the National Ignition Facility (NIF); however, modeling these fields and their advection is very computationally expensive on the temporal and spatial scales relevant for typical NIF hohlraum experiments (\textasciitilde 10 ns, \textasciitilde few mm). The hohlraum geometry also makes directly probing the fields somewhat challenging, limiting the available experimental data on these fields under NIF conditions. In particular, the relative contributions of frozen-in and Nernst advection of the field away from the hohlraum wall is not currently well understood. We have developed a new target platform for direct measurements of the field topology in a NIF-relevant configuration. Using a single cone of NIF, a 2.5 mm long, 5.4 mm diameter Au ring is illuminated with a similar beam geometry to that of one ring of beams in a full-scale hohlraum experiment. The ring target has no end caps, providing a clear line of sight for probing through the ring. A D$^{\mathrm{3}}$He filled exploding pusher placed \textasciitilde 5 cm below the ring is illuminated by an additional 60 beams of NIF to produce protons, some of which propagate through the ring. [Preview Abstract] |
Monday, October 23, 2017 3:24PM - 3:36PM |
CO8.00008: Positron Radiography of Ignition-Relevant ICF Capsules Jackson Williams, Hui Chen, John Field, Nino Landen, David Strozzi X-ray [1] and neutron [2] radiography are currently used to infer residual ICF shell and fuel asymmetries and areal density non-uniformities near and at peak compression that can impede ignition. Charged particles offer an alternative probe source that, in principle, are capable of radiographing the shell shape and areal density at arbitrary times, even in the presence of large x-ray self-emission. Laser-generated positrons are evaluated as a source to radiograph ICF capsules where current ultraintense laser facilities are capable of producing $2 \times 10^{12}$ relativistic positrons in a narrow energy bandwidth and short duration. Monte Carlo simulations suggest that both the areal density and shell radius can be reconstructed for ignition-relevant capsules conditions between 0.002-2 g/cm$^2$, and that this technique might be better suited to direct-drive. [1] R. Tommasini, et al. Development of Compton radiography of inertial confinement fusion implosions. Phys. Plasmas, 18(5):056309, 2011. [2] C. B. Yeamans, D. L. Bleuel, and L. A. Bernstein. Enhanced NIF neutron activation diagnostics. Rev. Sci. Instrum., 83(10):10D315, 2012. [Preview Abstract] |
Monday, October 23, 2017 3:36PM - 3:48PM |
CO8.00009: Advances in Modeling Direct-Drive Ignition at the National Ignition Facility T.J.B. Collins, J.A. Marozas Polar direct drive (PDD) makes it possible to perform direct-drive--ignition experiments at the National Ignition Facility (NIF) while the facility is configured for indirect drive. We present for the first time PDD ignition-relevant target designs with decreased laser intensities. These designs include the physical effects of cross-beam energy transfer (CBET) and nonlocal heat transport, both of which substantially affect the target drive. In the PDD configuration, a multiwavelength detuning strategy was found to be effective in mitigating the loss of coupling caused by CBET, allowing for implosion speeds comparable to those of previous designs. Target designs will be presented that span the region from alpha-particle heating to ignition. In addition, ignition-relevant designs will also be discussed for use in symmetric direct drive on the NIF. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 23, 2017 3:48PM - 4:00PM |
CO8.00010: A Statistical Approach to Implosion Design on the OMEGA Laser V. Gopalaswamy, R. Betti The 1-D campaign on OMEGA is backed by a novel approach aimed at producing an iterative and data-driven process to design optimized cryogenic implosions and improve the accuracy of 1-D physics models. The process does not preclude the possibility of significant systematic errors on OMEGA, nor does it assume that the hydrodynamic codes used in implosion design have all the necessary physical models. It only assumes that there exists some relationship between simulation and experimental results and uses statistical methods to model this relationship. Comparisons of hydrodynamic simulations of less-accurate physical models with more-accurate ones indicate that as long as equation of state is relatively well modeled, this assumption holds. By incorporating data from over 40 experiments on OMEGA, this approach has been used to design four targets with a two-shock pulse design for the 1-D campaign, and led to pre-shot predictions of yields within 5{\%} and ion temperatures within 3{\%} of the experimental values. One of these implosions has also produced the highest neutron yield ($1.1\times 10^{14})$ on an OMEGA cryogenic implosion with an areal density of $\sim 105\,{\mbox{mg}} \mathord{\left/ {\vphantom {{\mbox{mg}} {\mbox{cm}}}} \right. \kern-\nulldelimiterspace} {\mbox{cm}}^{2}$. The region of design space in which the predictive capability of this model is valid remains an open question. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 23, 2017 4:00PM - 4:12PM |
CO8.00011: Three-Dimensional Hydrodynamic Simulations of the Effects of Laser Imprint in OMEGA Implosions I.V. Igumenshchev, E.M. Campbell, V.N. Goncharov, S.P. Regan, A. Shvydky, A.J. Schmitt Illumination of direct-drive implosion targets by the OMEGA laser introduces large-amplitude broadband modulations in the absorbed energy from the largest (target size $\sim $900-$\mu $m) to smallest (speckle size $\sim $2-$\mu $m) spatial scales. These modulations ``imprint'' perturbations into a target that are amplified because of the secular and Rayleigh--Taylor growths during acceleration and deceleration of the target. The degradation of performance of room-temperature and cryogenic OMEGA implosions caused by these perturbations were simulated in three dimensions using the code \textit{ASTER}. The highest-resolution simulations resolve perturbation modes as high as $\ell \sim 200.$ The high modes $\ell \sim 50\;\,\mbox{to}\,\;100$ dominate in the perturbation spectrum during the linear growth, while the late-time nonlinear evolution results in domination of modes with $\ell \sim 30\;\,\mbox{to}\,\;50$. Smoothing by spectral dispersion reduces the linear-phase mode amplitudes by a factor of $\sim 4$ and results in substantial improvements in implosion performance that is in good agreement with measurements. The effects of imprint on implosion performance are compared with the effects of other implosion asymmetries, such as those induced because of laser beam imbalance, mistiming and mispointing, and target offset. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 23, 2017 4:12PM - 4:24PM |
CO8.00012: The Effect of Laser Imprint in OMEGA Cryogenic Implosions P.B. Radha, S.X. Hu, R. Betti, E.M. Campbell, C.J. Forrest, V.N. Goncharov, J.P. Knauer, R.L. McCrory, D.T. Michel, S.P. Regan, T.C. Sangster, C. Stoeckl, J.A. Frenje, M. Gatu Johnson, R.D. Petrasso Single laser beam nonuniformity (laser imprint) can potentially compromise direct-drive implosion performance. Rayleigh--Taylor growth of short-wavelength nonuniformity imposed by laser speckle can grow during the acceleration phase of an implosion, resulting in a tenuous in-flight shell. Significant laser imprint can result in a thicker in-flight shell; reduced fusion yield, areal density, and ion temperature; wider burn; and a larger hot-spot radius than a stable shell. Simulations with the hydrodynamic code \textit{DRACO} are presented for OMEGA cryogenic implosions spanning a range in adiabat and implosion velocity. These simulations include a three-dimensional ray trace. These simulations also include the effect of nonlocal heat conduction and cross-beam energy transfer. Signatures of laser imprint in cryogenic implosions are identified and comparisons to experimental observables are presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA000194. [Preview Abstract] |
Monday, October 23, 2017 4:24PM - 4:36PM |
CO8.00013: Dependence of Shock Timing on Coronal Parameters for OMEGA Direct-Drive Implosions D. Cao, T.R. Boehly, P.B. Radha, D.N. Polsin, S.P. Regan, V.N. Goncharov Accurate shock timing is essential to produce the desired isentrope or adiabat $\alpha $, of an inertial confinement fusion implosion. However, plasma formation and its effects on shock timing are not fully understood, leaving an area of interest for improving shock-timing predictive capability. This study examines the shock-timing sensitivity of two key coronal feature parameters that can be potentially inferred experimentally: conduction-zone length $D_{\mbox{c}} $ and coronal temperature $T_{\mbox{c}} .$ The former includes the plasma formation rate and influences the time between laser incidence and shock formation at the ablation surface, while the latter can influence shock strength. A two-picket implosion was simulated that had plasma profiles developing differing $D_{\mbox{c}} $ and $T_{\mbox{c}} $ after the end of the first picket (the profiles were otherwise identical). After launching the 2nd picket, correlations between the subsequent shock-merger time and main shock speeds (i.e., the observables with the VISAR diagnostic) to $D_{\mbox{c}} $ and $T_{\mbox{c}} $ are then calculated and in future experiments will be validated to improve code-predictive capability. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, October 23, 2017 4:36PM - 4:48PM |
CO8.00014: Asymetrically driven implosion experiment on the Laser M\'{e}gaJoule Franck Philippe, Patricia Seytor, Veronique Tassin, Rudolf Rosch, Bruno Villette We report on the results of the first implosion experiments performed on the Laser M\'{e}gaJoule (LMJ) facility. Their main purpose was to study implosion with large polar asymmetries of incident radiative flux on a capsule, while preserving azimuthal symmetry, in the context of ICF. In these experiments, one quad of LMJ is focused axially on a gold shield inside a hohlraum. The shield effectively divides the hohlraum in two compartments, and a capsule placed in the second compartment is indirectly driven by the x-ray flux generated in the first one. The subsequent asymmetric implosion is backlit by an x-ray source generated by another quad of LMJ and imaged with an x-ray microscope coupled to a framing camera. Time-gated x-ray radiographs of the imploding capsule and diode array measurements of the hohlraum x-ray emission are found to be in good agreement with FCI2 radiative hydrodynamics simulations. [Preview Abstract] |
Monday, October 23, 2017 4:48PM - 5:00PM |
CO8.00015: Experimental Results from the High-Adiabat Cryogenic Implosion Campaign on OMEGA J.P. Knauer, R. Betti, V. Gopalaswamy, M.J. Bonino, E.M. Campbell, T.J.B. Collins, C.J. Forrest, V.Yu. Glebov, V.N. Goncharov, D.R. Harding, J.A. Marozas, F.J. Marshall, P.W. McKenty, P.B. Radha, S.P. Regan, T.C. Sangster, C. Stoeckl The 1-D cryogenic experiments at the Omega Laser Facility are designed to systematically explore implosions where the multidimensional effects are small. These are typically high-adiabat ($\alpha \sim 7)$ implosions where the implosion velocity is varied. The implosion velocity is increased by thinning the cryogenic DT layer and using larger diameter targets that increase the coupling of laser energy. Data are used to develop a predictive model for the 1-D implosion series. Experimental data are shown for implosion velocities from 350 to 500 km/s that give neutron yields $>10^{14}.$ This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
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