Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session NO04: Magneto-Inertial FusionLive Streamed
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Chair: Jonathan Davies, LLE Room: Ballroom 111 A |
Wednesday, October 19, 2022 9:30AM - 9:42AM |
NO04.00001: Investigating at-scale MagLIF preheat on the NIF Bradley B Pollock, Ellie Tubman, Michael E Glinsky, Matthew R Weis, Adam J Harvey-Thompson, Kris Beckwith, Evstati G Evstatiev, David J Ampleford, Ryan Y Lau, James S Ross, David J Strozzi, John D Moody Recent experiments with D2-filled gas pipe targets at the NIF have continued to investigate laser preheating at parameters relevant to 40+ MA MagLIF designs. The experiments span a range of 1.6-4.8 mg/cc fill densities, and measure time-resolved laser propagation and burnthrough in a 1 cm-long target. One of the most significant uncertainties in previous coupling estimates is the energy deposition into the tube entrance window material, which is predicted in simulations to be of order ~few kJ but which is difficult to measure directly. By employing the NIF Visar system to measure the shock strength when the heated plasma reaches the wall of the target, the total energy deposited into the gas can be more accurately determined. These measurements are compared with 2D and 3D Hydra simulations. |
Wednesday, October 19, 2022 9:42AM - 9:54AM |
NO04.00002: Scaling of laser plasma instabilities in MagLIF preheat with applied magnetic field Jeffrey Fein, Adam J Harvey-Thompson, Matt Weis, Matthew R Gomez, Aaron Hansen, Stephanie M Miller, Dana H Edgell, Mingsheng Wei Experiments were executed on the Omega laser to study laser-plasma instabilities (LPIs) in magnetized gas tubes relevant to preheat in MagLIF. The study of how LPI and associated loss mechanisms vary with applied magnetic fields and other key variables will inform efforts to scale MagLIF to higher performance and assess potential mitigation strategies. We present initial data from the experiments, which indicate significantly higher stimulated Brillouin backscatter levels in the and enhanced propagation in the deutreriumdeuterium gas with 40-T applied magnetic fields. The increased backscatter is possibly a result of reduced radial electron heat conduction leading to increased laser filamentation and whole-beam self-intensification.* |
Wednesday, October 19, 2022 9:54AM - 10:06AM |
NO04.00003: Helical deformation of 3D defect in premagnetized Z-pinch liner Edmund P Yu, Thomas J Awe, Gabriel A Shipley, Maren W Hatch The magnetized liner inertial fusion (MagLIF) concept uses an azimuthal magnetic field (Bθ) to compress a metallic liner containing fusion fuel. A key component of MagLIF is an axial magnetic field Bz, permeating both the fuel and surrounding liner, which reduces the compression necessary to achieve fusion conditions. Experiments demonstrate that a liner premagnetized with Bz develops a helical instability with a pitch significantly larger than predicted by magnetohydrodynamic (MHD) theory. The cause of the helical instability remains an open research question. In this work, we examine the possible role of three-dimensional (3D) defects, which commonly occur in metals, as a seed for the helical instability. In general, a defect constitutes a nonlinear perturbation to the electrical current flow, which initiates a 3D feedback loop that allows the defect to grow and transform. In this work, we use 3D MHD simulations to examine how Bz modifies this feedback loop, thus causing a defect to deform helically. Simulation predictions can be tested experimentally, through visible emission imaging. |
Wednesday, October 19, 2022 10:06AM - 10:18AM |
NO04.00004: Investigating the role of magnetic flux compression in the formation of helical structures in axially magnetized implosions Matthew R Gomez, David A Yager-Elorriaga, Matthew R Weis, Christopher A Jennings, Nathaniel D Hamlin, Matthew R Martin, Gabriel A Shipley, Edmund P Yu, David J Ampleford, Kristian Beckwith Helical structures have been observed in axially magnetized liner implosions on the Z facility despite the azimuthal driving magnetic field being orders of magnitude larger than the applied axial magnetic field. One hypothesis to explain this result is magnetic flux is compressed by low density plasma against the surface of the target, resulting in an axial field that is much larger than the applied value. To test this hypothesis, experiments were conducted with a smaller volume of available flux, which simulations indicated would reduce the axial component of the magnetic field at the target surface. A comparison of the observed helical structures between the two cases will be presented. |
Wednesday, October 19, 2022 10:18AM - 10:30AM |
NO04.00005: Development of Cobalt-doped Be for MagLIF experiments on the Z-machine Eric C Harding, Jeff Fein, Adam J Harvey-Thompson, Kurt Tomlinson, Don Hashiguchi, Robert Kusner, Jacob Huxel We report on the development of a new Cobalt-doped Beryllium alloy (known as CoBe) for use in fusion experiments on the Z-machine. Beryllium is presently used as a target material in a fusion concept known as magnetized liner inertial fuson (MagLIF). In this concept a clyindrically imploding Be tube (or "liner") compresses and heats deuterium fuel to thermonuclear conditions. Previous experiments have shown that the inner surface of the tube mixes with the hot fuel at stagnation. To better diagnose the Be mix we dispersed Co throughout the bulk of the Be tube. By capturing images and spectra of the Co K-shell emission (7 keV) we then can infer the position and conditions of the Be mix. Experiments planned for August 2022 will be the first to test the new CoBe alloy. |
Wednesday, October 19, 2022 10:30AM - 10:42AM |
NO04.00006: Diagnostic application of Kr K-Shell x-ray tracer spectroscopy in MagLIF experiments at Z Jason Clapp, Roberto C Mancini, Eric C Harding, Adam J Harvey-Thompson In a series of MagLIF experiments performed at the Z pulsed power facility of Sandia National Laboratories beryllium liners filled with deuterium gas densities in the 0.7 to 1.4 mg/cc range, and a tracer amount of krypton were imploded. At the collapse of the cylindrical implosion temperatures in the 1 – 3 keV range and atom number densities of ∼1023 cm−3 were expected. The plasma was magnetized with a 10 T axial magnetic field. Krypton K-shell line emission was recorded with the CRITR time-integrated transmission crystal x-ray spectrometer. The observation shows n=2-1 line emissions in B-, Be, Li- and He-like Kr ions, and is characteristic of the highest electron temperatures achieved in the thermonuclear plasma. Detailed modeling of the observation based on krypton atomic and radiation physics demonstrates that the spectrum is temperature dependent. Since the observation is time-integrated, we perform the analysis with single- and multi-temperature models. We will discuss the limitations of single-temperature results, as well as the characteristics of extended analysis performed with two-temperature models. |
Wednesday, October 19, 2022 10:42AM - 10:54AM |
NO04.00007: Analysis of the scattered neutron energy spectrum from magnetized liner inertial fusion implosions on Z Owen M Mannion, David J Ampleford, Gordon A Chandler, Gary W Cooper, Matthew R Gomez, Christopher A Jennings, Patrick F Knapp, Michael Mangan, Jose Torres, Gary M Whitlow The neutron energy spectrum emitted from magnetized liner inertial fusion (MagLIF) implosions performed at the Z machine are made using a suite of neutron time of flight (nToF) detectors located along both axial and radial lines of sight. Measurements of the primary deuterium-deuterium (DD) fusion neutron energy spectrum are routinely used to infer the fusion yield and the hot spot apparent ion temperature. In this work, measurements of the scattered neutron energy spectrum will be used to study the conditions of the dense beryllium liner which surrounds and inertially confines the hot spot plasma in these experiments. Specifically, the beryllium liner areal density is inferred by measuring the ratio of the fusion yield to the number of scattered neutrons. Results from experiments using different initial target aspect ratios will be presented and a comparison will be made between measurements along the axial and radial nTOF lines of sight. |
Wednesday, October 19, 2022 10:54AM - 11:06AM |
NO04.00008: Signatures of azimuthal plasma asymmetries in the secondary DT neutron spectra of magnetized implosions at the NIF Brandon J Lahmann, John D Moody, Benjamin Bachmann, Hong W Sio, Edward P Hartouni, David J Strozzi, Laurent Divol, Aidan C Crilly, Brian Appelbe Secondary DT neutrons have proven to be an important diagnostic for magnetized implosions using D2 fuel both at the Z facility [1] and the NIF [2]. These neutrons are generated from 1 MeV D(D,p)T tritons streaming through the background plasma and are sensitive to the burn-averaged density, temperature, and magnetic fields in the hot spot. Core magnetic fields of ~ 5 kT, arising from the compressed externally applied seed field, can strongly impact the paths of these tritons which is reflected in the resultant secondary neutron spectra. Recent magnetized implosion experiments on the NIF have generated skewed equatorial secondary DT neutron spectra not seen in previous experiments. This skew implies some significant azimuthal asymmetry in the conditions probed by the tritons. We use 3D Monte-Carlo modeling as well as mix inferences from x-ray imaging to investigate potential explanations for the observed skews, including suppression of fill-tube mix. This work was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344 and LDRD project SI-2020-002. |
Wednesday, October 19, 2022 11:06AM - 11:18AM |
NO04.00009: Spatial and Temporal Neutron Measurements on the Fusion Z-pinch Experiment (FuZE) Amanda E Youmans, Thibault A Laplace, Josh A Brown, Bethany L Goldblum, James M Mitrani, Aria R Johansen, Pi-En Tsai, Brian A Nelson, Benjamin J Levitt, Drew P Higginson Nuclear fusion is a source of clean energy with many concepts in development. The Fusion Z-pinch Experiment (FuZE) is a sheared-flow stabilized Z-pinch device where the Portable and Adaptable Neutron Diagnostics for ARPA-E (PANDA) suite has been deployed since 2021 at the Zap Energy, Inc. facility. The FuZE capacitor banks are discharged to ionize neutral deuterium gas and induce pinch currents that cause fusion in deuterium plasmas. Neutrons with mean energies of 2.45 MeV are the only reaction product that can be detected outside of the device chamber. There are two types of neutron detectors in PANDA: fast plastic scintillators and lanthanum bromide (LaBr3) activation detectors. 16 gain matched plastic scintillator detectors are fielded at FuZE to calculate the isotropy of emitted neutron energies and verify the thermonuclear origin of neutron emission. The time resolved axial profile of the neutron source is measured by placing the same detectors along the pinch region in the z axis of FuZE to determine where the plasma is hot and dense enough to produce neutrons. A cross-calibrated LaBr3 activation detector measures the neutron yield for each discharge. These measurements are integrated with other diagnostics for a robust understanding of device performance. |
Wednesday, October 19, 2022 11:18AM - 11:30AM |
NO04.00010: Neutron source reconstruction of one-dimensional neutron images through maximum likelihood methods Sidney Ricketts, Michael Mangan, David N Fittinghoff, David J Ampleford The one-dimensional imager of neutrons (ODIN) has been used to image neutrons emitted from the source of Magnetized Liner Inertial Fusion (MagLIF) experiments on the Z facility. These experiments produce DD-neutrons which pass through a 100-mm thick tungsten rolled edge slit to then be imaged on CR-39 detectors. A piece of high-density polyethylene is used as a neutron to proton convertor to improve the CR-39 detection efficiency. The latent tracks within the CR-39 are exposed using a chemical etching process and recorded using an optical scanning system. The data, consisting of track diameter, eccentricity, position, and contrast, is down selected for primary DD-neutrons expected to have traveled directly from the through the slit assemble to the detector. The selected data is binned and integrated along the resolving axis to produce an axial detector response. A mathematical model of the instrument response function has been developed which is used with existing ODIN data to perform neutron source profile recovery via a maximum likelihood method assuming Gaussian noise. |
Wednesday, October 19, 2022 11:30AM - 11:42AM |
NO04.00011: Comparisons of Kinetic Effects on Heat Transport to Classical Fluid Models in Magnetized Gaspipes on NIF Ryan Y Lau, David J Strozzi, Mark Sherlock, William A Farmer, Yuan Shi We present simulations of heat flow relevant to magnetized gaspipe experiments on NIF to investigate kinetic effects on transport phenomena. These D2 and CH filled gas pipe targets are used to study the laser preheat stage of a MagLIF scheme where an axial magnetic field is applied to the target[1]. Initial simulations of these gas pipes were done with MHD code Gorgon[2] with a collision-dominated fluid model. However, the Knudsen number, the ratio between the electron mean free path and temperature scale lengths, was found to exceed 0.01 in substantial regions of space indicating the regime where non-local effects are important for heat flow. Non-local effects are a primary candidate for why the observed heat |
Wednesday, October 19, 2022 11:42AM - 11:54AM |
NO04.00012: Assessing the Validity of the Staged Z-Pinch with FLASH: Preliminary Simulations Fernando Garcia Rubio, Edward C Hansen, Kasper Moczulski, Petros Tzeferacos, Paul Ney, Emil Ruskov, Hafiz U Rahman In the last decade, the staged Z-pinch (SZP)[1] has emerged as a potential high-gain magneto-inertial fusion energy concept. Its attractiveness lies in its simplicity that neither an external preheat mechanism nor fuel magnetization is required. Instead, shock preheat and enough magnetic-field diffusion through the high atomic number liner are predicted to adequately magnetize the fuel. Calculations using the MACH2 code computed high gains (84 to 400 MJ)[2]–[4] for different liner materials using a pulsed-power machine comparable to Sandia’s Z facility. The validity of these simulations, however, has been put in question recently[5] when a potential verification issue concerning the use of the MACH2 code was suggested. The counter-arguments opposed to this criticism[6] have brought up a thrilling and enriching discussion in the community. In this talk, we discuss the first steps of an independent evaluation of the SZP using the radiation magnetohydrodynamic code FLASH. We focus on the main issue highlighted in the critique—adequately capturing the dynamics of the shock waves. For this purpose, we first present MACH2–FLASH comparisons of test problems and analytical solutions (magnetized Noh Z-pinch[7] and nonequilibrium radiative shock[8]) to subsequently address ideal gas simulations of the SZP2 scheme (silver liner). From an implosion perspective, this scheme is essentially a shock problem because Ohmic heating plays a secondary role. [1] H. U. Rahman et al., Phys. Plasmas 26, 052706 (2019).
[2] H. U. Rahman et al., J. Plasma Phys. 75, 749 (2009).
[3] F. J. Wessel et al., IEEE Trans. Plasma Sci. 43, 2463 (2015).
[4] F. J. Wessel et al., AIP Conf. Proc. 1721, 060002 (2016).
[5] I. R. Lindemuth, M. R. Weis, and W. L. Atchison, Phys. Plasmas 25, 102707 (2018).
[6] E. Ruskov, P. Ney, and H. U. Rahman, Phys. Plasmas 27, 042709 (2020).
[7] A. L. Velikovich et al., Phys. Plasmas 19, 012707 (2012).
[8] R. B. Lowrie, and J. D. Edwards, Shock Waves 18, 129 (2008).
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