T. P. Intrator

Los Alamos National Laboratory, Лос-Аламос, California, United States

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Publications (121)110.7 Total impact

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    ABSTRACT: In this community white paper, we describe an approach to achieving fusion which employs a hybrid of elements from the traditional magnetic and inertial fusion concepts, called magneto-inertial fusion (MIF). The status of MIF research in North America at multiple institutions is summarized including recent progress, research opportunities, and future plans.
    Full-text · Article · Nov 2015 · Journal of Fusion Energy
  • T. E. Weber · T. P. Intrator · R. J. Smith
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    ABSTRACT: Injection of plasma via an annular array of coaxial plasma guns during the pre-ionization phase of field-reversed configuration (FRC) formation is shown to catalyze the bulk ionization of a neutral gas prefill in the presence of a strong axial magnetic field and change the character of outward flux flow during field-reversal from a convective process to a much slower resistive diffusion process. This approach has been found to significantly improve FRC formation in a conical θ-pinch, resulting in a ∼350% increase in trapped flux at typical operating conditions, an expansion of accessible formation parameter space to lower densities and higher temperatures, and a reduction or elimination of several deleterious effects associated with the pre-ionization phase.
    No preview · Article · Apr 2015 · Physics of Plasmas
  • Jason Sears · T P Intrator · Y Feng · H O Swan · J Klarenbeek · K Gao
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    ABSTRACT: The momentum balance of a plasma pinch in the Reconnection Scaling Experiment (RSX) is examined in three dimensions using several repositionable, insertable probes. A new camera-based system described here triangulates the locations of the probe tips so that their measurements are spatially registered. The optical system locates probes to within ±1.5 mm of their absolute 3D position in the vessel and to within ±0.7 mm relative to other probes, on the order of the electron inertial length (1-2 mm).
    No preview · Article · Oct 2014 · Review of Scientific Instruments
  • J Sears · Y Feng · T P Intrator · T E Weber · H O Swan
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    ABSTRACT: A large 3D data set has been assembled using the relaxation scaling experiment (RSX) device to study the dynamics of flux ropes. In a series of single flux rope experiments, we have measured induced eddy currents inside the plasma that complicate the evolution of a nominally simple current system. It is also likely that the nominal MHD force balance is violated on ion inertial length scales. These phenomena appear irreducibly three dimensional.
    No preview · Article · Aug 2014 · Plasma Physics and Controlled Fusion
  • T.E. Weber · T.P. Intrator
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    ABSTRACT: A compact ionization gauge has been developed to carry out in situ measurements of high density (1020–1022 m−3) neutral gas flow dynamics with high temporal and spatial resolution. Key design aspects are discussed including gauge sensitivity and time response scaling with decreased probe dimensions, high-pressure operation, improved driver circuit bandwidth, and techniques for constructing a miniaturized probe head. Gas adsorption was discovered to significantly alter emission current and gauge sensitivity over timescales of several seconds. This effect must be taken into consideration when making time-resolved, high-density measurements. Over short timescales gauge response was predicted by scaling the sensitivity of a nominal Bayard-Alpert gauge to account for variations in probe dimensions and species-dependent ionization cross-section. Time-resolved neutral density profiles have been acquired in the Magnetized Shock Experiment at Los Alamos National Laboratory, providing data on the initial conditions of the ionization, plasmoid formation, and translation processes. It is shown that the desired density profiles can be achieved using a dynamic gas fill and that density can be scaled independently of the spatial profile.
    No preview · Article · Apr 2014 · Review of Scientific Instruments
  • T. P. Intrator · L. Dorf · X. Sun · Y. Feng · J. Sears · T. Weber
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    ABSTRACT: Two magnetic flux ropes that collide and bounce have been characterized in the laboratory. We find screw pinch profiles that include ion flow , magnetic field , current density , and plasma pressure. The electron flow can be inferred, allowing the evaluation of the Hall term in a two fluid magnetohydrodynamic Ohm's Law. Flux ropes that are initially cylindrical are mutually attracted and compress each other, which distorts the cylindrical symmetry. Magnetic field is created via the induction term in Ohm's Law where in-plane (perpendicular) shear of parallel flow (along the flux rope) is the dominant feature, along with some dissipation and magnetic reconnection. We predict and measure the growth of a quadrupole out-of-plane magnetic field δBz . This is a simple and coherent example of a shear flow driven dynamo. There is some similarity with two dimensional reconnection scenarios, which induce a current sheet and thus out-of-plane flow in the third dimension, despite the customary picture that considers flows only in the reconnection plane. These data illustrate a general and deterministic mechanism for large scale sheared flows to acquire smaller scale magnetic features, disordered structure, and possibly turbulence. v i B J v e J × B ∇ × v e × B
    No preview · Article · Apr 2014 · Physics of Plasmas
  • T. P. Intrator · X. Sun · L. Dorf · J. A. Sears · Y. Feng · T. E. Weber · H. O. Swan
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    ABSTRACT: Flux ropes form basic building blocks for magnetic dynamics in many plasmas, are macroscopic analogues of magnetic field lines, and are irreducibly three dimensional (3D). We have used the relaxation scaling experiment (RSX) to study flux ropes, and have found many new features involving 3D dynamics, kink instability driven reconnection, nonlinearly stable but kinking flux ropes, and large flows.
    No preview · Article · Dec 2013 · Plasma Physics and Controlled Fusion
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    Yan Feng · J. Goree · Bin Liu · T. P. Intrator · M. S. Murillo
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    ABSTRACT: Stochastic transport of a two-dimensional (2D) dusty plasma liquid with a perpendicular magnetic field is studied. Superdiffusion, which is a type of non-Fickian transport, is found to occur especially at higher magnetic fields with $\beta$ of order unity. Here, $\beta = \omega_c / \omega_{pd}$ is the ratio of the cyclotron and plasma frequencies for dust particles. The mean-square displacement ${\rm {MSD}} = 4 D_\alpha t^\alpha$ is found to have an exponent $\alpha > 1$, indicating superdiffusion, with $\alpha$ increasing monotonically to $1.1$ as $\beta$ increases to unity. The 2D Langevin molecular dynamics simulation used here also reveals that another indicator of random particle motion, the velocity autocorrelation function (VACF), has a dominant peak frequency $\omega_{peak}$ that empirically obeys $\omega_{peak}^2 = \omega_c^2+ \omega_{pd}^2/4$.
    Full-text · Article · Nov 2013 · Physical Review E
  • X. Sun · T. P. Intrator · M. Liu · J. Sears · T. Weber
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    ABSTRACT: In nature and many laboratory plasmas, a magnetic flux tube threaded by current or a flux rope has a footpoint at a boundary. The current driven kink mode is one of the fundamental ideal magnetohydrodynamic instabilities in plasmas. It has an instability threshold that has been found to strongly depend on boundary conditions (BCs). We provide a theoretical model to explain the transition of this threshold dependence between nonline tied and line tied boundary conditions. We evaluate model parameters using experimentally measured plasma data, explicitly verify several kink eigenfunctions, and validate the model predictions for boundary conditions BCs that span the range between NLT and LT BCs. Based on this model, one could estimate the kink threshold given knowledge of the displacement of a flux rope end, or conversely estimate flux rope end motion based on knowledge of it kink stability threshold.
    No preview · Article · Nov 2013 · Physics of Plasmas
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    M. R. Brown · P. K. Browning · M. E. Dieckmann · I. Furno · T. P. Intrator
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    ABSTRACT: In this article, we discuss the idea of a hierarchy of instabilities that can rapidly couple the disparate scales of a turbulent plasma system. First, at the largest scale of the system, L, current carrying flux ropes can undergo a kink instability. Second, a kink instability in adjacent flux ropes can rapidly bring together bundles of magnetic flux and drive reconnection, introducing a new scale of the current sheet width, ℓ, perhaps several ion inertial lengths (δ i ) across. Finally, intense current sheets driven by reconnection electric fields can destabilize kinetic waves such as ion cyclotron waves as long as the drift speed of the electrons is large compared to the ion thermal speed, v D ≫v i . Instabilities such as these can couple MHD scales to kinetic scales, as small as the proton Larmor radius, ρ i .
    Full-text · Article · Oct 2013 · Space Science Reviews
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    ABSTRACT: Magneto-inertial fusion (MIF) approaches take advantage of an embedded magnetic field to improve plasma energy confinement by reducing thermal conduction relative to conventional inertial confinement fusion (ICF). MIF reduces required precision in the implosion and the convergence ratio. Since 2008 (Wurden et al 2008 IAEA 2008 Fusion Energy Conf. (Geneva, Switzerland, 13–18 October) IC/P4-13 LA-UR-08-0796) and since our prior refereed publication on this topic (Degnan et al 2008 IEEE Trans. Plasma Sci. 36 80), AFRL and LANL have developed further one version of MIF. We have (1) reliably formed, translated, and captured field reversed configurations (FRCs) in magnetic mirrors inside metal shells or liners in preparation for subsequent compression by liner implosion; (2) imploded a liner with interior magnetic mirror field, obtaining evidence for compression of a 1.36 T field to 540 T; (3) performed a full system experiment of FRC formation, translation, capture, and imploding liner compression operation; (4) identified by comparison of 2D-MHD simulation and experiments factors limiting the closed-field lifetime of FRCs to about half that required for good liner compression of FRCs to multi-keV, 1019 ion cm−3, high energy density plasma (HEDP) conditions; and (5) designed and prepared hardware to increase that closed-field FRC lifetime to the required amount. Those lifetime experiments are now underway, with the goal of at least doubling closed-field FRC lifetimes and performing FRC implosions to HEDP conditions this year. These experiments have obtained imaging evidence of FRC rotation, and of initial rotation control measures slowing and stopping such rotation. Important improvements in fidelity of simulation to experiment have been achieved, enabling improved guidance and understanding of experiment design and performance.
    No preview · Article · Aug 2013 · Nuclear Fusion
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    ABSTRACT: Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics(®). In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field.
    No preview · Article · Apr 2013 · The Review of scientific instruments
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    ABSTRACT: form only given. The objective of the Field-Reversed Configuration Heating Experiment (FRCHX) is to obtain a better understanding of the fundamental scientific issues associated with high energy density plasmas (HEDPs) in strong, closed-field-line magnetic fields. These issues have relevance to such topics as magneto-inertial fusion (MIF), laboratory astrophysical research, and intense radiation sources, among others. To create the HEDP, a field-reversed configuration (FRC) plasma of moderate density is first formed via reversed-field theta pinch. It is then translated into a cylindrical aluminum shell (solid liner), where it is trapped between two magnetic mirrors and then compressed by the magnetically-driven implosion of the shell. A requirement is that once the FRC is stopped within the shell, the trapped flux inside the FRC must persist while the compression process is completed. With the present shell dimensions and drive bank parameters, the total time required for implosion is ~25 microseconds. Lifetime measurements of recent FRCHX FRCs indicate trapped lifetimes now approaching ~14 microseconds, and with recent experimental modifications the liner compression can be initiated considerably earlier before formation is completed in order to close that gap further. A discussion of FRC lifetime-limiting mechanisms will be presented along with a description of FRCHX and recent changes that have been made to it. Results from recent experiments aimed at lengthening FRC lifetime will also be presented.
    No preview · Conference Paper · Jan 2013
  • Y. Feng · T.P. Intrator · J. Sears · T. Weber · K. Gao
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    ABSTRACT: form only given. The generation and destruction of magnetic field is an important feature of solar, magnetosphere and cosmic plasmas, for example during reconnection, dynamo, and turbulent processes. We have experimentally measured spatially resolved profiles of magnetic flux ropes. These data include ion flow, magnetic field, current density, and plasma pressure, which allow us to verify a screw pinch equilibrium and also infer the electron fluid flow in three dimensions. Parallel currents along each flux rope result in a mutual attraction, which compresses and distorts the cylindrically symmetric equilibrium profiles. The electron and ion fluid flows turn out to be different, and we show that sheared axial electron fluid flow v_e generates magnetic field B(t) via the induction term curl X̅v_e X B = -curl X E = dB/dt. Data show a quadrupole out of plane magnetic field signature with four fold symmetry that is driven by flux rope flows with two fold symmetry. This mechanism provides a natural and general mechanism for large scale sheared flows to acquire smaller scale magnetic features, disordered structure, and possibly turbulence.
    No preview · Conference Paper · Jan 2013
  • J. Sears · T. P. Intrator · G. Wurden · T. E. Weber · W. Daughton · J. Klarenbeek · K. Gao
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    ABSTRACT: A plasma column is generated in a longitudinal magnetic field in the Reconnection Scaling Experiment such that current can be drawn along the column axis. At low current density, the column remains straight. At current density slightly above the external kink limit, the column deforms with azimuthal wavevector m = 1. The amplitude of the deformation saturates and the column gyrates at a steady rate for many periods. The instability sometimes gives way to a higher-order mode. At higher current density still, the column disrupts. To investigate the saturated non-ideal behavior we measure the vector magnetic field and the plasma temperature and density in a cubic volume measuring 0.1 m on a side with resolution on the order of the electron skin depth. Our 3D probe positioning system uses stereo camera vision to precisely situate the probe tips. Study of the saturated kink mode in laboratory plasma may offer clues to the long lifetime of astrophysical jets.
    No preview · Article · Oct 2012
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    ABSTRACT: The AFRL Shiva Star capacitor bank (1300 microfarads, up to 120 kilovolts) operated typically with 4 to 5 megajoules of electrically stored energy, with axial discharge currents of 10 to 15 megamps, and current rise times of approximately 10 microseconds, has been used to drive metal shell (solid liner) implosions in several geometries, including long cylindrical designs, which are suitable for compression of axial magnetic fields to multi-megagauss levels. Such imploding liners are also suitable for compressing magnetized plasmas to magneto-inertial fusion conditions. Magneto-Inertial Fusion (MIF) approaches take advantage of embedded magnetic field to improve plasma energy confinement by reducing thermal conduction relative to conventional inertial confinement fusion (ICF). MIF reduces required implosion speed and convergence ratio relative to ICF. AFRL, its contractors and collaborating institutions LANL, UNM, and UNR have developed one version of magnetized plasmas at pre-compression densities, temperatures, and magnetic fields that may be suitable for such compression. These are Field Reversed Configurations (FRCs). This effort reliably formed, translated, and captured FRCs in magnetic mirrors inside10 cm diameter, 30 cm long, mm thick metal shells or liners in preparation for subsequent compression by liner implosion; imploded a liner with an interior magnetic mirror field, obtaining evidence for compression of 1.36 T field to approximately 500 T; performed a full system experiment of FRC formation, translation, capture, and imploding liner compression operation; identified by comparison of 2D-MHD simulation and FRC capture experiments factors limiting the closed- field lifetime of FRCs to about half that required for good liner compression of FRCs to multi-keV, 1019 ion/cm3, high energy density plasma (HEDP) conditions; and designed and prepared hardware to increase that closed field FRC lifetime to the required amount. Those lifetime e- tension experiments have obtained imaging evidence of FRC rotation (which is a phenomenon that limits such closed field lifetimes), and of initial rotation control measures slowing and stopping such rotation. These and the results of subsequent closed field plasma lifetime and compression experiments and related simulations will be discussed.
    No preview · Conference Paper · Oct 2012
  • T. Intrator · T. Weber · K. Gao · C. Yoo · J. Klarenbeek
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    ABSTRACT: We describe several technology advances that we believe will be helpful for Magneto Inertial Fusion (MIF) experiments. We are developing plasma guns to improve the startup and flux trapping for magnetized plasma field reversed configuration (FRC) targets for MIF compression. This should aid initial pre ionization, freezing in of bias flux, line tie each end to the middle to retard toroidal rotation, and provide end shorting of radial electric fields. We are also developing a novel magnetic field diagnostic that uses a tiny section of Terbium doped optical fiber as a Faraday rotation medium. The optical path and hardware is inexpensive and simple, and has a small form factor that will fit inside a MagLIF capsule, and can be radation hardened. Low noise, optically coupled magnetic field measurements will be possible for vacuum MaGLIF shots.
    No preview · Article · Oct 2012
  • J. Sears · T. P. Intrator · G. Wurden · T. E. Weber · W. Daughton · J. Klarenbeek · K. Gao
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    ABSTRACT: A column of plasma generated in a longitudinal magnetic field in the Reconnection Scaling Experiment suffers from a catastrophic external kink instability when sufficient current density is driven along its length. At slightly lower current density but still above the Kruskal-Shafranov stability limit, we observe the amplitude of the kink to saturate at a, where a is the radius of the current distribution, and the column to gyrate at a steady rate for many periods. We evaluate how saturation of the kink mode is influenced by axial flow and shear therein, by rotation and Coriolis force, and by kinetic effects beyond the fluid regime. The plasma column of length l = 0.48 m has electron temperature Te = 10 eV and density ne = 1e19 m-3. The background axial field is B = 0.01 T, and the saturated steady state occurs for current I = 300 A. We measure the vector magnetic field and the plasma temperature and density in a cubic volume measuring 0.1 m on a side with resolution on the order of the electron skin depth. From these measurements we derive the flow. We present also results of a 2D numerical model simulated with the VPIC code. Study of the saturated kink mode in laboratory plasma may offer clues to the long lifetime of astrophysical jets.
    No preview · Article · Oct 2012
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    ABSTRACT: The measurement and simulation of the three-dimensional structure of magnetic reconnection in astrophysical and lab plasmas is a challenging problem. At Los Alamos National Laboratory we use the Reconnection Scaling Experiment (RSX) to model 3D magnetohydrodynamic (MHD) relaxation of plasma filled tubes. These magnetic flux tubes are called flux ropes. In RSX, the 3D structure of the flux ropes is explored with insertable probes. Stereo triangulation can be used to compute the 3D position of a probe from point correspondences in images from two calibrated cameras. While common applications of stereo triangulation include 3D scene reconstruction and robotics navigation, we will investigate the novel application of stereo triangulation in plasma physics to aid reconstruction of 3D data for RSX plasmas. Several challenges will be explored and addressed, such as minimizing 3D reconstruction errors in stereo camera systems and dealing with point correspondence problems.
    No preview · Article · Oct 2012
  • K. W. Gao · T. P. Intrator · T. E. Weber · C. B. Yoo · J. Klarenbeek
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    ABSTRACT: The MagLIF experiment is an approach to Magneto Inertial Fusion (MIF) that will compress a laser preheated magnetized plasma inside a small sub cm size beryllium capsule and the magnetic field inside. A good measurement of the compressed magnetic field will help us understand how the compression proceeds, and the time scale over which field diffuses out. We are working on a first step to the direct measurement of vacuum magnetic field (expected to be mostly Bz) compression time history, potentially space-resolved, without a plasma fill. A small magneto-active section of optical fiber can measure magnetic fields in the 1-1000 Tesla range. Directly measured vacuum Bz is an initial but important step towards validating the codes supporting MagLIF. The technology will use a Terbium doped optical fiber as a Faraday rotation medium. The optical path and hardware is simple, inexpensive, and small enough to fit inside a MagLIF capsule, and can be radiation hardened. Low noise, optically coupled magnetic field measurements will be possible for vacuum MagLIF shots.
    No preview · Article · Oct 2012