Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session CO09: ICF: Magneto-Inertial FusionLive
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Chair: Kelly Hahn, LLNL |
Monday, November 9, 2020 2:00PM - 2:24PM Live |
CO09.00001: Exploring improved simulation techniques for analysis and design of auto-magnetizing liner experiments Gabriel Shipley, Thomas Awe, Brian Hutsel, John Greenly, Stephen Slutz Auto-magnetizing (AutoMag) liners are designed to produce strong internal axial magnetic field (30-100 T) to premagnetize the fuel in MagLIF without external coils. AutoMag liners are made of discrete helical conductors encapsulated by electrically insulating material. Initially, internal axial field is generated as current flows through the conductors. When the driver current rises more rapidly, the insulating material undergoes dielectric flashover (ceasing axial field production) and the helical liner implodes. Dielectric breakdown is notoriously difficult to model; thus, experiments are crucial to developing and tuning simulations. Recent AutoMag experiments on the Mykonos accelerator (800 kA, 100 ns) diagnosed the evolution of dielectric breakdown with photodiodes and 12 frame gated imaging; data have helped to construct a novel method for approximating the AutoMag flashover process in MHD simulations. The method is based on insertion of ``broken down'' insulator material at prescribed moments during the current pulse (informed by experimental data). Implementation has improved agreement of simulations with data captured on Z. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. [Preview Abstract] |
Monday, November 9, 2020 2:24PM - 2:36PM Live |
CO09.00002: Origin of Helical Instability Modes in Premagnetized Thin-Foil Liner Z-pinches Using PERSEUS Jeff Woolstrum, Charles Seyler, Ryan McBride In z-pinch-driven liner implosion experiments with a pre-imposed axial magnetic field, helical magneto-Rayleigh-Taylor (MRT) instability structures have been observed. We show that the formation of these helical structures can be described using Hall magnetohydrodynamics (MHD). Additionally, the use of Hall MHD leads to an axial asymmetry in the trailing spikes of the MRT structure. This asymmetry, with rolled-up wavelike features, has also been observed in experiments and is likely related to the mode-merger process observed in MRT instability evolution. We used the 3D extended MHD simulation code PERSEUS (which includes Hall physics) [C. E. Seyler and M. R. Martin, Phys. Plasmas \textbf{18}, 012703 (2011)] to study these helical instabilities and asymmetries. We also show that the so-called Hall instability is responsible for producing helically bunched plasma around the z-pinch which causes a bunching of magnetic field and current. This allows for the seeding of the helical pitch angle in the electron flow and therefore current, which seeds the pitch angle of the helical instability without the need for significant axial magnetic flux compression. This is a new explanation for the origin of the helical instabilities observed in axially premagnetized z-pinch implosions. This work was supported by the NNSA SSAP under DOE Cooperative Agreement DE-NA0003764. [Preview Abstract] |
Monday, November 9, 2020 2:36PM - 2:48PM Live |
CO09.00003: Simulation of FuZE pinch axisymmetric stability using gyrokinetic and extended-MHD models V. I. Geyko, J. R. Angus, M. A. Dorf Axisymmetric $(m=0)$ gyrokinetic and extended-MHD simulations of the shear flow stabilized Z-pinch plasmas are performed with the high-order finite volume code COGENT. A prominent feature of this work is that the radial profiles for the plasma density and temperature are taken from the recent experimental data and the magnetic field profile is obtained as a solution of the MHD force balance equation. Such an approach allows to address realistic plasma parameters and provide insights into the current and planned experiments. In particular, it is demonstrated that the radial profiles play an important role in stabilization, as the embedded guiding center (ExB) drift has a strong radial shear, which can contribute to the Z-pinch stabilization even in the absence of the fluid flow shear. As the result, the stability properties become dependent of the sign of the fluid flow velocity and a modest fluid shear might even play a destabilizing role. These results are supported by both the MHD and gyrokinetic simulations. It is also shown that the linear modes are not stabilized by a moderate (up to a sound speed) fluid shear flow. The nonlinear stabilization, however, can be achieved for short wavelength modes, which is demonstrated in both models. [Preview Abstract] |
Monday, November 9, 2020 2:48PM - 3:00PM Live |
CO09.00004: Exploring the physics of compressible Kelvin-Helmholtz Instability in magnetized laser-produced plasma. Victorien Bouffetier, Alexis Casner, Luke Ceurvorst, Hong Sio, Jonathan Peebles, Vladimir Smalyuk, Omar Hurricane The Kelvin-Helmholtz Instability (KHI) is a key mechanism responsible of energy transfer from the large fluid scales to the kinetic scales. The instability is present in numerous systems such as stellar physics in the study of coronal mass ejections in solar flares to the Earth's magnetosphere reconnection physics for example. Due to the complexity of this phenomenon, the study of the KHI in a controlled way appears necessary to obtain a better understanding of its development. The stabilizing effect of applied magnetic field on KHI is well known since Chandrasekhar's seminal book, but no experimental benchmarks have been made under intense magnetic fields. The case of compressible magnetized KHI is even unexplored and is then of interest. We propose here to present an experimental design and MHD simulations performed with the FLASH code [1] for the study of the compressible KHI when an intense magnetic field is applied. The presented framework will be experimentally tested on OMEGA laser facility. \newline [1] P. Tzeferacos et al, Physics of Plasmas, 24(4):041404, 2017 [Preview Abstract] |
Monday, November 9, 2020 3:00PM - 3:12PM Live |
CO09.00005: Two-dimensional temperature spatial profiles and gradients in laser-heated plasmas relevant to MagLIF Kyle Carpenter, Roberto Mancini, Eric Harding, Adam Harvey-Thompson, Matthias Geissel, Matthew Weis, Stephanie Hansen, Kyle Peterson, Gregory Rochau We present measurements of two-dimensional temperature spatial profiles from magnetized and unmagnetized plasma experiments performed at Z relevant to the pre-heat stage of Magnetized Liner Inertial Fusion. The D gas fill was doped with a trace amount of Ar for spectroscopy purposes and time-integrated spatially resolved spectra and narrowband images were collected in both experiments. Individual analysis of the spatially resolved spectra recovers temperature profiles T$_{\mathrm{e}}$(z) that are resolved along the axial direction of laser propagation but spatially integrated along the instrument's line-of-sight. By including both the spectrum and image data in a multi-objective analysis, we have extracted two-dimensional electron temperature distributions T$_{\mathrm{e}}$(r,z). The results indicate that, by inhibiting radial thermal conduction, the magnetic field increased T$_{\mathrm{e}}$, the axial extent of the laser heating, and the magnitude of the radial temperature gradients. Comparisons with simulations reveal that the simulations over-predict the extent of the laser heating and under-predict the temperature. Temperature gradient scale lengths extracted from the measurements also permit an assessment of the importance of nonlocal heat transport. [Preview Abstract] |
Monday, November 9, 2020 3:12PM - 3:24PM Live |
CO09.00006: Formation of Supersonic Spherically Imploding Plasma Liners on PLX Samuel Langendorf, Tom Byvank, John Dunn, Franklin Witherspoon, Andrew Case, Edward Cruz, Mark Gilmore The Plasma Liner Experiment (PLX) at Los Alamos National Laboratory is a mid-size experimental facility that has been built to explore the idea of using a spherically imploding plasma liner, formed via the merging of discrete plasma jets, as a transformative driver for magneto-inertial fusion. [1] We present first results from PLX with fully spherical plasma liner implosions, at the culmination of an upgrade process to equip the facility with a spherical array of 36 plasma guns. Prior investigations on PLX have studied the merging of smaller numbers of plasma jets, and indicated the possible important role of inter-jet streaming and interpenetration between merging jets, and the possible impact that these physics may have in decreasing detrimental density perturbations due to shock waves. We will present diagnostic results to determine if this smoothing of the liner density profile has indeed been achieved in the fully spherical case. [1] Hsu, Scott C., et al. "Spherically imploding plasma liners as a standoff driver for magnetoinertial fusion." IEEE Transactions on Plasma Science 40.5 (2012): 1287-1298. We acknowledge the critical contributions of the many scientists and personnel in the broader team and plasma physics community who have contributed to the PLX-ALPHA program. [Preview Abstract] |
Monday, November 9, 2020 3:24PM - 3:36PM Live |
CO09.00007: High Energy Preheat Configurations for MagLIF Matthew Weis, Adam Harvey-Thompson, Daniel Ruiz Three-dimensional HYDRA calculations were carried out to identify achievable laser preheat energies for the Magnetized Liner Inertial Fusion (MagLIF) platform under the assumption of various upgrades to the Z-Beamlet laser, up to a 6.3 kJ laser pulse. The simulations assumed a $\sim500$ nm laser entrance foil enabled by cryogenic cooling and a 1.5 mm laser spot produced by a distributed phase plate. Smaller laser spot sizes showed significant self-focusing that limited energy deposition to the imploding deuterium fuel region. With larger spot sizes, simulations suggest that laser pulses ranging from 2.6 to 6.3 kJ can robustly couple $\sim75$~\% of the incident energy to the fuel, with the remainder lost to the laser entrance window. When compared to 2D simulations, 3D simulations predict similar coupled energies to the fuel but also consistently show more radial filamentation and spray of the beam as the magnetic field is increased. This may cause additional mix from the liner walls and introduce vorticity into the fuel. In the absence of these effects, the calculated achievable preheat energies applied to implosion calculations suggest that a 6.3 kJ Z-Beamlet laser is sufficient to optimize MagLIF performance at 20 MA for a variety of fuel densities and applied field strengths. [Preview Abstract] |
Monday, November 9, 2020 3:36PM - 3:48PM Live |
CO09.00008: The Effect of LEH Foil Thickness on MagLIF-Relevant Laser Preheat Adam Harvey-Thompson, Matthew Weis, Daniel Ruiz, Mingsheng Wei, Adam Sefkow, Taisuke Nagayama, Michael Campbell, Julie Fooks, Michael Glinsky, Kyle Peterson The Magnetized Liner Inertial Fusion (MagLIF) scheme relies on coupling laser energy to an underdense fuel to raise the fuel adiabat at the start of the implosion. To deposit energy into the fuel the laser must first penetrate a laser entrance hole (LEH) foil which can absorb energy and introduce mix. We report on a series of experiments where a single beamline from the OMEGA-EP laser was coupled into Ar-filled gas cells. The LEH foil thickness containing the Ar was varied from 0.5-3 \textmu m. Time-gated x-ray images captured the extent of the laser-heated plasma channel as a function of time. Two-dimensional (2D) HYDRA simulations accurately predicted the extent of the plasma channel for the 0.5 \textmu m and 1 \textmu m LEH foil cases but exhibited excessive self-focusing for the 2 \textmu m and 3 \textmu m LEH foil cases. This was corrected for the 2 \textmu m LEH foil case by using a more conductive model for the LEH foil material. However, 3D simulations were required to reproduce the data for the 3 \textmu m LEH foil case. This work highlights the challenges of simulating multi-micron thick LEH foils but gives confidence that simulations can capture energy deposition into MagLIF-relevant targets. [Preview Abstract] |
Monday, November 9, 2020 3:48PM - 4:00PM Live |
CO09.00009: Simulations of Laser Preheat Effects on Yield in mini-MagLIF Implosions at Omega Luis Leal, Andrei Maximov, Edward Hansen, Jonathan Davies, Daniel Barnak, Jonathan Peebles, Adam Sefkow, Riccardo Betti Experiments on OMEGA have shown that DD neutron yield in mini-MagLIF (magnetized liner inertial fusion) implosions increases with preheat laser energy; however, beyond a certain preheat energy yield falls again, faster than predicted by published MagLIF simulations. Past mini-MagLIF simulations have been able to explain the trend in yield as the applied magnetic field is varied without the preheat laser$^{\mathrm{1}}$. Three-dimensional HYDRA simulations, including the preheat laser, are presented that reproduce the observed trend. The effects varying the preheat laser energy has on neutron-averaged parameters such as ion temperature, areal density, and field compression are discussed, as well as the importance of the Nernst term on the dynamics of the magnetic field during the preheat stage. The possible effects of wall mix into the fuel is also investigated in simulations, including a fuel region doped by possible mix elements that can enter into the fuel region. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. $^{\mathrm{1}}$E. C. Hansen et al., Phys. Plasmas 27, 062703 (2020). [Preview Abstract] |
Monday, November 9, 2020 4:00PM - 4:12PM Live |
CO09.00010: Simulations Demonstrating Extended MHD Effects During the Laser Preheat Stage of MagLIF Experiments and Electro-Thermal Instability Growth Within MagLIF Liners with an Applied Axial Field Aidan Boxall, Jeremy Chittenden, Brian Appelbe We present results from simulations of MagLIF experiments at Sandia National Laboratory, using an extended MHD version of the 3D Gorgon code which includes the full Braginskii form of Ohm's law and associated magnetized heat flow. The effects of the Nernst, cross-Nernst and magnetized heat flow on the laser preheat stage of the implosion are investigated. Electro-thermal instability growth in the presence of an axial field is also studied. Resistive volumetric perturbations were added to replicate the effects of liner impurities. The volumetric perturbations redirect the current to flow around them. With an applied axial field the total magnetic field on the liner edge is helical. Redirected current flowing parallel to the helical field experiences a reduced Lorentz force compared to current redirected to flow perpendicular to the magnetic field. This variation in the Lorentz force alters the vaporization rate of the liner. This may provide a helical bias to the electrothermal instability growth to seed the helical MRT growth observed in experiments. [Preview Abstract] |
Monday, November 9, 2020 4:12PM - 4:24PM Live |
CO09.00011: Laser coupling and window mixing in NIF MagLIF gas pipe experiments Bradley Pollock, Michael Glinsky, Matthew Weiss, Stephanie Hansen, Steven Ross, John Moody Recent MagLIF gas pipe experiments at the NIF have continued to investigate laser energy coupling into the target gas fill. One of the most significant uncertainties in the coupling is the energy deposition into the window material, which is predicted in simulations to be or order \textasciitilde 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. Additionally, in some experiments the target entrance window has had a mid-Z tracer added to track the depth of window material propagation into the target, allowing for assessments of window mixing with the gas fill. Preliminary data indicate that the window material does not propagate further than \textasciitilde 2 mm into the target, and that the mixing depth is dependent on the initial gas pressure inside the pipe.$\backslash $This work was performed under theĀ auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, November 9, 2020 4:24PM - 4:36PM Live |
CO09.00012: Magnetized Plasma Guns for the PLX PJMIF Project F.D. Witherspoon, A. Case, E. Cruz, M. Luna, A. Cook, R. Becker In plasma jet driven magneto-inertial fusion (PJMIF), an array of discrete supersonic plasma jets is used to form a spherically imploding plasma liner, which then compresses a magnetized plasma target to fusion conditions[1]. We plan to form the target by stagnating a number of magnetized plasma jets in the center of the target chamber. Magnetized coaxial plasma guns are being developed by adapting the previously developed contoured gap plasma liner gun to form a magnetized plasma jet by adding a bias field coil to the gun. We aim to achieve a magnetized hydrogen plasma jet with $\sim$ 3 $\times$ 10$^{14}$~cm$^{-3}$ muzzle density, temperature above 5 eV, 100 km/s, with an embedded field of $\sim$ 1 kG. We will provide an overview of the experimental results, along with plans for providing up to 12 magnetized guns to LANL for a planned integrated liner-on-target experiment on PLX using the 36 liner guns installed from the ALPHA program[2]. [1] Hsu et al., IEEE Trans. Plasma Sci.~{\bf 40}, 1287 (2012). [2] Yates et al., Phys. Plasmas \textbf{27}, 062706 (2020). [Preview Abstract] |
Monday, November 9, 2020 4:36PM - 4:48PM Live |
CO09.00013: Increasing stability and maintaining performance of magneto-inertial fusion targets via self-similar scaling strategies D. E. Ruiz, P. F. Schmit, D. A. Yager-Elorriaga Magneto-inertial fusion (MIF) concepts, such as the Magnetized Liner Inertial Fusion (MagLIF) platform [M. R. Gomez et al, Phys. Rev. Lett. \textbf{113}, 155003 (2014)], constitute a promising avenue for achieving ignition and significant fusion yields in the laboratory. Under constraints imposed by capabilities of present-day pulsed-power facilities, increasing the performance and stability of MIF targets remains an important and challenging task. In this talk, we present a theoretical framework for scaling MIF-target parameters with respect to target radius and liner density while maintaining self-similar implosion trajectories. We provide analytical estimates for the scaling of energy losses and fusion performance metrics. Specifically, while holding peak current, laser preheat energy, and liner material fixed, we show that decreasing the initial target radius $R_0$ leads to increases in target robustness to hydrodynamical instabilities and maintains target performance by enabling thicker (smaller aspect ratio) liners and higher driver pressures, respectively. We compare our results to numerical simulations. [Preview Abstract] |
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