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 BI01: ICF: Implosions, Burn, and InstabilitiesInvited Live
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Chair: Hans Rinderknecht, Laboratory for Laser Energetics - Rochester Room: Ballroom B |
Monday, November 8, 2021 9:30AM - 10:00AM |
BI01.00001: How the concepts of coast-time and radius peak of velocity were key to achieving capule gain >-5 in inertially confined fusion Invited Speaker: Omar A Hurricane Conventional belief in inertial confinement fusion (ICF) is that high laser power and low DT fuel adiabats are required for obtaining ignition. The textbooks in ICF make no mention of the concept of “coast-time,” yet implosion experiments on the NIF have repeatedly show better success with higher adiabat designs driven to very short coast-times. Understanding why took time. |
Monday, November 8, 2021 10:00AM - 10:30AM |
BI01.00002: Producing a burning plasma via inertial confinement fusion implosions within a shaped I-Raum radiation cavity Invited Speaker: James S Ross A burning deuterium and tritium (DT) plasma, in which the heating from fusion produced alpha particles exceeds the compressional work done on the reacting plasma, has been achieved for the first time via the inertial confinement approach at the National Ignition Facility. One of the major obstacles to achieving a burning plasma is maintaining the implosion symmetry of larger capsule targets. In this work, the symmetry was controlled using a shaped radiation cavity (i.e., hohlraum), known as an I-Raum [1], and by using cross beam energy transfer. The I-Raum reduces the radiation drive asymmetry produced by the 3 incident laser cones by adding recessed cavities to the traditional cylindrical hohlraum at the location of the two outer laser cones. This offset the bubble of absorbing plasma created at these locations and enables the central inner laser cone to propagate to the waist of the I-Raum allowing improved radiation drive symmetry over the timescale required to implode a 1.1X larger scale capsule. |
Monday, November 8, 2021 10:30AM - 11:00AM |
BI01.00003: Observation of "suprathermal" ion kinetic energy in Inertial Confinement Fusion (ICF) implosions at the National Ignition Facility (NIF). Invited Speaker: Edward P Hartouni Recent experiments conducted on the NIF have achieved burning plasmas, plasmas for which the dominant energy evolves from fusion itself. Neutron time-of-flight measurements of the plasma flow burn-averaged velocities developed for the ICF program at NIF provide a part per 10,000 measurement precision of the collective plasma motion, as well as a 2 keV precision of the mean neutron kinetic energy. This new diagnostic capability reveals that “high performing” ICF implosions depart from the “hydrodynamic” expectation relating the neutron mean energy to the ion temperature. This departure is a signature of an ion kinetic energy population increase over the Maxwellian behavior of a hydrodynamic plasma. |
Monday, November 8, 2021 11:00AM - 11:30AM |
BI01.00004: Simultaneous inference of multiple stagnation performance metrics in Magnetized Liner Inertial Fusion Experiments using Bayesian Data Assimilation Invited Speaker: Patrick F Knapp The Magnetized Liner Inertial Fusion (MagLIF) concept being explored on the Z machine at Sandia National Laboratories is a promising route to achieving high fusion yields (>>1 MJ) on a future pulsed power generator. MagLIF uses the current supplied by Z to compress a preheated and pre-magnetized cylindrical beryllium liner containing fusion fuel. A pre-imposed axial magnetic field (Bz,o) acts to insulate the hot fuel from the cold liner, allowing PdV work to raise the fuel temperature via compression by the magnetically driven liner. This concept has shown exciting performance gains in recent years demonstrating Gbar pressures and confinement of charged fusion products at stagnation. However direct experimental measurement of critical performance metrics has remained elusive. Here we demonstrate a Bayesian data assimilation technique that is able to simultaneously infer these key metrics (e.g., stagnation pressure, mix, confinement properties, etc.) with rigorously defined uncertainties by self-consistently matching x-ray power, x-ray imaging, x-ray spectral, neutron yield, and neutron spectral diagnostics through a reduced model of the system. Extensive testing using analytic models as well as 1D and 3D MHD calculations is shown. We apply this tool to a large suite of MagLIF experiments and examine trends in performance and stagnation properties with input conditions such as laser energy, magnetic field strength, fuel density, among others. We analyze these trends in the context of analytic scaling theory, exploring the impacts of multiple different potential degradation mechanisms. Finally, we examine the effects of three-dimensional structure on performance and provide a path towards better constraint of three-dimensional stagnation properties using synthetic experiments to guide diagnostic investments. |
Monday, November 8, 2021 11:30AM - 12:00PM |
BI01.00005: Using scaled power flow experiments at 20 MA to establish the efficacy of load current delivery on a >50 MA next-generation pulsed power facility Invited Speaker: Clayton E Myers The Z accelerator routinely delivers >20 MA of electrical current to centimeter-scale imploding loads. Such current delivery is made possible by the fact that the final transmission line operates in a magnetically insulated regime where charged particles are inhibited from crossing the anode-cathode gap and losses due to electrode plasma formation remain manageable. Achieving similarly effective load current delivery on a >50 MA next-generation accelerator would enable groundbreaking advances in high energy density science. To build confidence in taking this next step, it is essential to establish the efficacy of load current delivery through transmission lines operating at next-generation power flow conditions. Fortunately, such conditions can be created today at ~1/3 of the peak current by scaling down a >50 MA final transmission line both in radius to preserve the magnetic field, current density, and ohmic heating and in the anode-cathode gap to preserve the electric field. Here we report the results of the first scaled power flow experiments on Z, which are designed to test load current delivery between R = 15–27 mm on a ~60 MA accelerator. The current flowing through a 4-mm-long scaled transmission line with a 2-mm gap is measured in time and space using a line-imaging velocity interferometer. These measurements indicate that current coupling through the scaled transmission line is essentially lossless. A subsequent fourfold over-test of the electric field stress indicates a remarkable >80% current coupling through a 0.5-mm gap. The implications of the observed 80–100% coupling efficiencies are addressed with power flow theory and modeling. Finally, the design of future scaled experiments to test additional regions of a >50 MA final transmission line are presented. |
Monday, November 8, 2021 12:00PM - 12:30PM |
BI01.00006: Magnetohydrodynamic instabilities in ablation fronts and coronal plasmas Invited Speaker: Fernando Garcia Rubio We consider the effect of self-generated magnetic field (B) on ablation front and coronal instabilities in inertial confinement fusion (ICF) with semi-analytic methods. Experimental evidence of the spontaneous generation of B fields in coronal plasmas has been reported in the last decade., Among the different sources leading to spontaneous B-field generation, the so-called Biermann-battery effect, which is due to misalignment between gradients of temperature and density, plays a dominant role in the conduction layer separating the ablation front from the coronal plasma. These fields can play an important role in ICF implosions because they modify heat transfer to the target. However, their effect on the ablation front and coronal dynamics that are subject to hydrodynamic instabilities remains less clear. We propose a self-consistent fluid model of the conduction layer to assess the B-field effect during the linear stage of three main instabilities: ablation-front–driven Rayleigh–Taylor (RT), Darrieus–Landau (DL), and magnetothermal (MT). We find that the B-field effect on the RT instability depends exclusively on the Froude number (Fr). In the weak-acceleration, large-Fr regime, the B field plays a stabilizing role by shortening the range of unstable wavelengths. The DL instability, characteristic of flow configurations with energy deposition, remains unaffected by the B field. The MT instability is exclusively driven by the self-generated B field and only occurs in a region adjacent to the critical surface. The MT instability has always been characterized as convective. We prove for the first time its absolute character and we derive criteria for this instability to occur for short perturbation wavelengths. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856. |
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