T. P. Intrator

Los Alamos National Laboratory, Los Alamos, California, United States

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Publications (160)120.06 Total impact

  • 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.
    Plasma Physics and Controlled Fusion 08/2014; 56(9):095022. · 2.37 Impact Factor
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    ABSTRACT: The kinetic features of secondary magnetic reconnection in a single flux rope undergoing internal kink instability are studied by means of three-dimensional particle-in-cell simulations. Several signatures of secondary magnetic reconnection are identified in the plane perpendicular to the flux rope: a quadrupolar electron and ion density structure and a bipolar Hall magnetic field develop in proximity of the reconnection region. The most intense electric fields form perpendicularly to the local magnetic field, and a reconnection electric field is identified in the plane perpendicular to the flux rope. An electron current develops along the reconnection line, in the opposite direction of the electron current supporting the flux rope magnetic field structure. Along the reconnection line, several bipolar structures of the electric field parallel to the magnetic field occur, making the magnetic reconnection region turbulent. The reported signatures of secondary magnetic reconnection can help to localize magnetic reconnection events in space, astrophysical and fusion plasmas.
    Plasma Physics and Controlled Fusion 04/2014; 56(6):064010. · 2.37 Impact Factor
  • 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.
    Review of Scientific Instruments 01/2014; 85(4):043501-043501-6. · 1.60 Impact Factor
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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.
    Plasma Physics and Controlled Fusion 12/2013; 55(12):4005-. · 2.37 Impact Factor
  • 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.
    Physics of Plasmas 11/2013; 20(11):2106-. · 2.38 Impact Factor
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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 .
    Space Science Reviews 10/2013; 178(2-4):357-383. · 5.52 Impact Factor
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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.
    Nuclear Fusion 08/2013; 53(9):093003. · 2.73 Impact Factor
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    ABSTRACT: Flux ropes are bundles of magnetic field wrapped around an axis. Many laboratory, space, and astrophysics processes can be represented using this idealized concept. Here, a massively parallel 3D kinetic simulation of a periodic flux rope undergoing the kink instability is studied. The focus is on the topology of the magnetic field and its geometric structures. The analysis considers various techniques such as Poincaré maps and the quasi-separatrix layer (QSL). These are used to highlight regions with expansion or compression and changes in the connectivity of magnetic field lines and consequently to outline regions where heating and current may be generated due to magnetic reconnection. The present study is, to our knowledge, the first QSL analysis of a fully kinetic 3D particle in cell simulation and focuses the existing QSL method of analysis to periodic systems.
    Physics of Plasmas 08/2013; 20(8). · 2.38 Impact Factor
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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.
    The Review of scientific instruments 04/2013; 84(4):043507. · 1.52 Impact Factor
  • 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.
    Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
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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.
    Plasma Science (ICOPS), 2013 Abstracts IEEE International Conference on; 01/2013
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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.
    10/2012;
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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.
    10/2012;
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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.
    10/2012;
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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.
    10/2012;
  • T. P. Intrator, J. Sears, K. Gao, J. Klarenbeek, C. Yoo
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    ABSTRACT: In the Reconnection Scaling Experiment (RSX) we have measured out of plane quadrupole magnetic field structure in situations where magnetic reconnection was minimal. This quadrupole out of plane magnetic signature has historically been presumed to be the smoking gun harbinger of reconnection. On the other hand, we showed that when flux ropes bounced instead of merging and reconnecting, this signature could evolve. This can follow from sheared fluid flows in the context of a generalized Ohms Law. We reconstruct a shear flow model from experimental data for flux ropes that have been experimentally well characterized in RSX as screw pinch equilibria, including plasma ion and electron flow, with self consistent profiles for magnetic field, pressure, and current density. The data can account for the quadrupole field structure.
    10/2012;
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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.
    10/2012;
  • C. B. Yoo, K. W. Gao, T. E. Weber, T. P. Intrator
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    ABSTRACT: The Magnetized Shock Experiment (MSX) at Los Alamos National Laboratory requires remote diagnostics of plasma density. Laser interferometry can be used to determine the line-integrated density of the plasma. A multi-chord heterodyne fiber optic Mach-Zehnder interferometer is being assembled and integrated into the experiment. The advantage of the fiber coupling is that many different view chords can be easily obtained by simply moving transmit and receive fiber couplers. Several such fiber sets will be implemented to provide a time history of line-averaged density for several chords at once. The multiple chord data can then be Abel inverted to provide radially resolved spatial profiles of density. We describe the design and execution of this multiple fiber interferometer.
    10/2012;
  • T. Intrator, A. Lazarian, G. Lapenta
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    ABSTRACT: Turbulent Reconnection in Space and Laboratory Plasmas
    04/2012;
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    ABSTRACT: form only given. The Field-Reversed Configuration Heating Experiment (FRCHX) is a collaborative experiment between the Air Force Research Laboratory (AFRL) and Los Alamos National Laboratory (LANL) to study high energy density laboratory plasma (HEDLP) phenomena, which encompass such topics as magneto-inertial fusion (MIF). In this experiment, field-reversed configuration (FRC) plasmas are formed via a reversed-field theta pinch and then translated into a cylindrical aluminum shell (solid liner), where they are compressed by the magnetically-driven implosion of the shell. Representative parameters for the initial FRC plasmas are density 5 × 1016 ions/cm3, temperature ∼200 eV, poloidal magnetic field ∼1 T, length 15∼20 cm, and field exclusion radius ∼2 cm. To date, however, the trapped-flux lifetime of the FRC has been too short to allow it to undergo useful compression. New experimental hardware has been designed and fabricated to increase that lifetime, following four approaches: 1) improved plasma pre-ionization via RF and other pulsed axial electric field breakdown assistance, 2) use of an array of axial plasma guns to externally produce the initial plasma, 3) implementation of axial bias rings above the liner, used in conjunction with gas puff prefill, to control end shorting of the open magnetic field lines surrounding the FRC and thereby control its rotation, and 4) optimized bank timing and trapping fields. Results from recent tests focusing on extending FRC lifetime will be summarized, and an analysis of the new systems' effectiveness will be presented.
    Plasma Science (ICOPS), 2012 Abstracts IEEE International Conference on; 01/2012