Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session CO05: ICF: Magnetized Liner Inertial Fusion (MagLIF)On Demand
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Chair: Arijit Bose, University of Delaware Room: Rooms 306-307 |
Monday, November 8, 2021 2:00PM - 2:12PM |
CO05.00001: Developing a platform to enable higher input parameters in magnetized liner inertial fusion Matthew R Gomez, Matthew R Weis, Adam J Harvey-Thompson, Derek C Lamppa, Christopher A Jennings, Stephen A Slutz, Matthias Geissel, Jerry A Crabtree, Thomas J Awe, Ian C Smith, David J Ampleford, Kristian Beckwith Magneto-inertial fusion concepts utilize magnetic fields in imploding targets to reduce thermal conduction losses and relax fuel areal density requirements. In MagLIF [Slutz, et al., Phys. Plasmas 17, 056303 (2010)], an axial B-field is applied to a cm-scale beryllium liner containing fusion fuel. A kJ-class, few-ns laser preheats the fuel, and current from the Z machine drives the implosion. Performance is sensitive to the B-field, preheat energy, and load current, and significant improvements have been observed when all input parameters are increased together [Gomez, et al., Phys. Rev. Lett. 125, 155002 (2020)]. In early experiments these input parameters were 10 T, 0.5-1 kJ, and 16-18 MA, and subsequent efforts have increased them to 16 T, 1-1.4 kJ, 20 MA. Further platform development is underway with the goal of 20-21 T, 2-2.5 kJ, and 21 MA. To achieve these parameters, the applied B-field coil configuration has been updated, an improved cryogenic target was developed, and the transmission line and target geometry was modified. Individual tests of these improvements are in progress. Longer term goals include integrating these increases simultaneously and continued improvements to individual components. *SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 |
Monday, November 8, 2021 2:12PM - 2:24PM |
CO05.00002: Deep-Learning-Enabled Assessment of Magnetic Confinement in Magnetized Liner Inertial Fusion William E Lewis, Patrick F Knapp, Stephen A Slutz, Paul F Schmit, Gordon A Chandler, Matthew R Gomez, Adam J Harvey-Thompson, Michael A Mangan, David J Ampleford, Kristian Beckwith Magnetized Liner Inertial Fusion (MagLIF) is a magneto-inertial fusion (MIF) concept being studied on the Z-machine at Sandia National Laboratories. MagLIF relies on quasi-adiabatic heating of a gaseous deuterium (DD) fuel and flux compression of a background axially oriented magnetic field to achieve fusion relevant plasma conditions. The magnetic field-radius product (BR) at bang time determines the extent of confinement of charged fusion products and is thus of fundamental interest in understanding MagLIF performance. We surrogate expensive physics calculations of magnetized fast charged-particle transport and associated secondary neutron emission in MIF plasmas with an artificial neural network. This enables Bayesian inference of BR for a series of MagLIF experiments that systematically vary the laser preheat energy deposited in the target. We demonstrate fuel magnetization decreases with deposited preheat energy in a fashion consistent with Nernst advection of magnetic field out of the hot fuel and diffusion into the target liner. This constitutes the first ever systematic experimental study of the magnetic confinement properties as a function of fundamental inputs on any neutron-producing MIF platform. |
Monday, November 8, 2021 2:24PM - 2:36PM |
CO05.00003: Tomographic reconstruction of emission volumes of MagLIF plasmas from orthogonal projection data Jeffrey R Fein, Eric Harding, Christopher A Jennings We present our most recent attempts to reconstruct the emission volumes from Magnetized Liner Inertial Fusion (MagLIF) stagnation events using x-ray imaging data from two, orthogonal projection views. This work is needed to measure the three-dimensional shape of structures previously observed with only single-projection imaging. Our approach involves the comparison of several reconstruction techniques, including basis function expansions and Expectation-Maximization with a variety of regularization schemes that seek to incorporate physical constraints to improve uniqueness in this highly ill-posed inverse problem. Ultimately, we expect that an ensemble of solutions from a variety of reconstruction approaches can be used to estimate probability distributions of emission volumes and shape metrics with confidence intervals. |
Monday, November 8, 2021 2:36PM - 2:48PM |
CO05.00004: Investigating the energy balance in MagLIF preheat experiments Adam J Harvey-Thompson, Matthias Geissel, Matthew R Weis, Jerry A Crabtree, David J Ampleford, Thomas J Awe, Kristian Beckwith, Jeffrey R Fein, Matthew R Gomez, Joseph C Hanson, Christopher A Jennings, Mark W Kimmel, Andrew J Maurer, Jonathon E Shores, Ian C Smith, Robert R Speas, Christopher S Speas, Adam J York, John L Porter The Magnetized Liner Inertial Fusion (MagLIF) concept requires that multi-kJ of laser energy be coupled to the D2 fuel during the “preheat” stage. How efficiently laser energy is coupled into the gas is impacted by various loss mechanisms such as laser-plasma instabilities (LPI) and the need to penetrate through a laser entrance hole (LEH) foil. Recent experiments have employed cryogenic cooling enabling thinner, larger diameter LEH foils and larger spot-size laser beams. This has dramatically improved the measured coupling efficiency to ~88% from ~64% in the best performing warm configurations enabling >2 kJ to be coupled for the first time in integrated experiments. In this presentation we will discuss how the coupling efficiency is assessed, the various factors that impact the coupling efficiency and the implications. |
Monday, November 8, 2021 2:48PM - 3:00PM |
CO05.00005: Lasergate: a windowless gas target for enhanced laser preheat in Magnetized Liner Inertial Fusion Benjamin Galloway, Stephen A Slutz, Mark W Kimmel, Patrick K Rambo, Jens Schwarz, Matthias Geissel, Adam J Harvey-Thompson, Matthew R Weis, Christopher A Jennings, Ella Field, Damon Kletecka, Quinn Looker, Anthony P Colombo, Aaron Edens, Ian C Smith, Jonathon E Shores, Christopher S Speas, Robert R Speas, Andrew Spann, Justin Sin, Sophie Gautier, Vincent Sauget, Paul Treadwell, Gregory A Rochau, John L Porter At Sandia's Z Facility, the Magnetized Liner Inertial Fusion (MagLIF) program aims to study inertial confinement fusion in deuterium-filled gas cells by implementing a three-step process on the fuel: premagnetization, laser preheat, and Z-pinch compression. In the laser preheat stage, the Z-Beamlet laser focuses through a polyimide window to enter the gas cell and heat the fusion fuel. However, the presence of the few µm thick window reduces the laser energy coupled to the gas and causes window material to mix into the fuel. The Lasergate concept is designed to avoid these detrimental effects by "cutting" the window and allowing the interior gas pressure to push the window material out of the beam path just before the heating laser arrives. We present proof-of-principle experiments to evaluate a laser-cutting approach to Lasergate and explore the subsequent window and gas dynamics. Further, an experimental comparison of gas preheat with and without Lasergate gives clear indications of an energy deposition advantage using the Lasergate concept, as well as other observed and hypothesized benefits. While Lasergate was conceived with MagLIF in mind, the method is applicable to any laser or diagnostic application requiring direct line of sight to the interior of gas cell targets. |
Monday, November 8, 2021 3:00PM - 3:12PM |
CO05.00006: Maximization of Laser Coupling with Cryogenic Targets Matthias Geissel, Adam J Harvey-Thompson, Matthew R Weis, J. Allen Crabtree, David J Ampleford, Thomas J Awe, Kristian Beckwith, Jeffrey R Fein, Matthew R Gomez, Joseph C Hanson, Christopher A Jennings, Mark W Kimmel, Andrew J Maurer, Jonathon E Shores, Ian C Smith, Robert R Speas, Christopher S Speas, Adam J York, John L Porter A major obstacle for depositing laser energy to targets in Magnetized Liner Inertial Fusion (MagLIF) is the need to contain the gas with a laser-entrance-hole window (LEH). With densities of 1.0-1.4 mg/cc at room temperature, previous experiments used a polyimide film of 1.56 µm thickness and 2.2 mm diameter which consumed about 1 kJ of laser energy at the maximum plausible beam spot size of 1.1 mm. |
Monday, November 8, 2021 3:12PM - 3:24PM |
CO05.00007: Investigating at-scale MagIF preheat on the NIF Bradley B Pollock, Eleanor Tubman, Michael E Glinsky, Matthew R Weis, Adam J Harvey-Thompson, Kristian Beckwith, Evstati G Evstatiev, David J Ampleford, Ryan Y Lau, James S Ross, David J Strozzi, John D Moody Recent experiments with CH and D2-filled gas pipe targets at the NIF have continued to investigate laser coupling at parameters relevant to 40+ MA MagLIF designs. At present, ~20 kJ energy coupling has been achieved at fill densities ~5 mg/cc in 1 cm-long CH-gas-filled targets. One of the most significant uncertainties in the coupling 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 accurately determined. These measurements are compared with x-ray imaging and time-resolved measurements of the laser propagation through the target, and to 2D and 3D simulations. |
Monday, November 8, 2021 3:24PM - 3:36PM |
CO05.00008: Using Ross filter pairs to observe wall mix in MagLIF experiments at the NIF Eleanor Tubman, Bradley B Pollock, David J Strozzi, John D Moody, James S Ross, Adam J Harvey-Thompson, Matthew R Weis, Michael E Glinsky, Stephanie B Hansen, Ryan Lau, Evstati G Evstatiev, David J Ampleford, Kristian Beckwith In the MagLIF ICF scheme, a cylindrical gas volume is laser heated before the walls of the cylinder are driven radially inward to compress the heated gas. Exploring the effects of material from the walls and the laser entrance window mixing into the heated region are important considerations for MagLIF experiments1,2,3,. The addition of these materials into the heated gas can potentially have detrimental effects, radiatively cooling the gas fill and degrading the yield. The NIF has been used to drive gas-pipe experiments where a tracer element (Ti) is placed on the LEH window or where strips of Ti and Sc are attached to the wall. Spatially and temporally resolved spectroscopic measurements of the Ti and Sc emission indicate the spatial location of these materials at various times during the interaction, assisting future predictions and mitigations of their propagation into the gas-pipe. |
Monday, November 8, 2021 3:36PM - 3:48PM |
CO05.00009: Line VISAR measurements of energy deposition for next generation MagLIF laser preheat at NIF Michael E Glinsky, Matthew R Weis, Adam J Harvey-Thompson, Kristian Beckwith, Bradley B Pollock, John D Moody, David J Strozzi Gas-pipe experiments on the NIF have investigated MagLIF laser preheat at scales relevant to next-generation pulsed-power facilities. Experiments have been done into magnetized (up to 28 Tesla), room temperature, hydrocarbon and unmagnetized D2 gases of densities that span 1.6 mg/cc to 4.8 mg/cc (5% to 16% critical electron density). Up to 30 kJ of energy from one quad has been delivered into an oval spot of 1580 micron mean diameter over a time of about 11 ns with a power of 2 TW and an intensity of 2 x 1014 W/cm2. A critical measurement in these experiments is the laser energy deposited though inverse Bremsstrahlung absorption in the gas. In this talk we describe line VISAR measurements taken in unmagnetized hydrocarbon-gas experiments. We show how the shock timing and velocity measured by line VISAR can be related to energy deposition over the 1 mm extent of the diagnostic view. |
Monday, November 8, 2021 3:48PM - 4:00PM |
CO05.00010: Measurements of Laser-Preheat–Induced Mix in Scaled Magnetized Liner Inertial Fusion Implosions Jonathan L Peebles, Daniel H Barnak, Peter V Heuer, Luis S Leal, Frederic J Marshall, Jonathan R Davies, Riccardo Betti Previous studies using the scaled-down magnetized linear inertial fusion platform at the Omega Laser Facility demonstrated significant yield enhancement with preheat and magnetization in cylindrical implosions. However, initial simulations indicating increased performance with preheat energy were not validated in the experiments. Further experiments performed using titanium tracer layers were used to ascertain if and how certain types of mix affected implosions. Measurements using a Fresnel zone plate and multipurpose spectrometer verified that mix from the interior wall of the cylinder was the primary cause of performance degradation, while simultaneously ruling out mix from preheat window material. |
Monday, November 8, 2021 4:00PM - 4:12PM |
CO05.00011: Simulations of Ti-Layered Magnetized Liner Inertial Fusion Implosions on OMEGA Investigating Effect of Mix Luis S Leal, Jonathan L Peebles, Jonathan R Davies, Daniel H Barnak, Peter V Heuer, Andrei V Maximov, Edward C Hansen, Adam B Sefkow, Riccardo Betti Magnetized liner inertial fusion (MagLIF) on OMEGA is a laser-driven platform used to study magneto-inertial fusion. Simulations of fully integrated MagLIF implosions describe a trend of decreasing DD neutron yields with increasing laser preheat energy, but overpredict the yield compared to experiments. To investigate the effect of mix, the experiments were performed with a capsule that included a Ti layer on its inner wall, and these experiments showed large yield degradation. Simulations with HYDRA were done for OMEGA MagLIF configurations with and without Ti layer and with varying fraction of Ti premixed into the fuel region. In simulations, the modeling of Ti layer alone does not reproduce the yield drop in experiment. Only simulations with Ti mixed in the fuel show the large yield drop indicating the importance of mix effects in OMEGA MagLIF. |
Monday, November 8, 2021 4:12PM - 4:24PM |
CO05.00012: Trends in 3D Simulations of MagLIF Matthew R Weis, David J Ampleford, Kristian Beckwith, Matthew R Gomez, Eric Harding, Adam J Harvey-Thompson, Christopher A Jennings, Daniel E Ruiz, Stephen A Slutz, David A Yager-Elorriaga Two-dimensional magneto-hydrodynamics (MHD) simulations, with codes such as HYDRA, are the primary tool for designing Magnetized Liner Inertial Fusion (MagLIF) [1] experiments on the Z machine at Sandia National Laboratories. However, experimental stagnation conditions and associated structures are better described by three-dimensional simulations that include the magneto-Rayleigh-Taylor instability (MRTI). Findings from a series of 3D HYDRA simulations will be shown that study how MagLIF target performance varies with initial seed on the liner surface as well as initial axial magnetic field strength. Results suggest that MRTI can explain experimental yield variability, although general matches with experiment are achieved without considering other degradation mechanisms such as mix. As the Bz field was scanned in 3D, the ion temperature increased with field strength, however the yield was essentially flat or reduced beyond 15 T which is unlike 2D simulations that generally show higher yield. The simulations suggest residual azimuthal flow in the fuel due to the laser deposition is responsible for a twisted Bz distribution in the fuel which leads to a much lower plasma beta (P_therm./P_mag. < 10) at stagnation. |
Monday, November 8, 2021 4:24PM - 4:36PM |
CO05.00013: Development and Implementation of a Resistive Hall MHD Extension to the Gorgon Code Aidan Boxall, Jeremy P Chittenden, Brian Appelbe, Griffin Farrow, Nikita Chaturvedi Hall MHD becomes significant in low-density regions of Z-pinches where the ion inertial length is comparable to the characteristic scale length [1]. We present a new method to include the Hall term and anisotropic conductivity in the extended MHD code Gorgon. The Hall term is challenging to model in low-density regions due to the electron drift velocity becoming unphysically large. To mitigate this a vacuum cut-off density is used. This method includes the Hall term as part of the conductivity tensor [2]. With this casting a more intuitive understanding of the formation of force free currents is gained. Force free currents may be significant for MagLIF instability growth [3]. Using Gorgon we have reproduced the results of whistler wave and Hall drift wave test problems. We investigate extending a Magnetic Rayleigh-Taylor test problem [1], including the Hall term, to include regions below the vacuum cut-off density. We also study the effects of Hall on MRT growth on Z-pinches such as Hall driven shear flow. |
Monday, November 8, 2021 4:36PM - 4:48PM |
CO05.00014: Origin of Helical Instabilities in Axially Premagnetized Thin-Foil Liner Z-pinch Implosions using Hall Magnetohydrodynamics Jeff M Woolstrum, Charles E Seyler, Ryan D McBride Helical magneto-Rayleigh-Taylor instability (MRTI) structures have been observed in z-pinch-driven liner implosion experiments with a pre-imposed axial magnetic field. We show that the formation of these helical structures can be described by a Hall magnetohydrodynamical (HMHD) model. We used the 3D extended magnetohydrodynamics simulation code PERSEUS (which includes Hall physics) [C. E. Seyler and M. R. Martin, Phys. Plasmas 18, 012703 (2011)] to study these helical instabilities and show that a Hall Instability in the low-density coronal plasma immediately surrounding the dense liner is responsible for producing helically bunched plasma striations and an associated magnetic field and current density. This seeds the helical pitch angle of the MRTI even when other proposed helical seeding mechanisms are either not present in the experiments or not accounted for in the simulations. For example, this mechanism does not require low-density power-feed plasmas to be swept in from large radius or the development of electrothermal instabilities. The Hall Instability is thus a new, independent explanation for the origin of the helical instabilities observed in axially premagnetized liner experiments. Simulation results supporting this mechanism are presented. |
Monday, November 8, 2021 4:48PM - 5:00PM |
CO05.00015: Numerical study of three-dimensional instability development in solid liner dynamic screw pinches Gabriel A Shipley, Paul F Schmit, Christopher A Jennings, David A Yager-Elorriaga, Daniel E Ruiz Magnetically driven liner implosions experience magneto-Rayleigh-Taylor instabilities (MRTI) which act to reduce liner integrity and thus fusion fuel compression and confinement in magneto-inertial fusion (MIF) experiments. As such, mitigating MRTI is important for the advancement of MIF concepts such as Magnetized Liner Inertial Fusion (MagLIF). Dynamic screw pinches (DSP) leverage magnetic field line tension to stabilize MRTI by employing an initially helical magnetic field to drive the implosion. The field polarization at the liner surface rotates during the implosion, distributing the stabilizing benefits of field-line tension across a larger portion of the MRTI mode spectrum. Although linear theory predicts significant reduction in cumulative MRTI growth compared to conventional z-pinch implosions, detailed numerical exploration of MRTI development in DSP is needed. We present results from three-dimensional magnetohydrodynamic simulations exploring MRTI reduction for a variety of DSP implosions. Accounting for physical effects such as nonlinear instability development, magnetic diffusion, shock dynamics, and material heating, the modeling we present provides a crucial advance in the DSP concept for use in liner implosion experiments, including potential MagLIF-like MIF experiments. |
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