Bulletin of the American Physical Society
59th Annual Meeting of the APS Division of Plasma Physics
Volume 62, Number 12
Monday–Friday, October 23–27, 2017; Milwaukee, Wisconsin
Session BP11: Poster Session I: Space and Astrophysical Plasmas; FRC; PMI; Energetic Particles; Other Concepts; Measurement and Diagnostic Techniques; Laser-Plasma Instabilities |
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Room: Exhibit Hall D |
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BP11.00001: SPACE AND ASTROPHYSICAL PLASMAS |
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BP11.00002: Gravity Acceleration and Gravity Paradox Han Hanyongquan, Tang Yuteng The magnitude of the gravitational acceleration of the earth is derived from low of universal gravitation. If the size and mass of the gravitational force are proportional to any situation, then the celestial surface gravity is greater than the celestial center near the gravity, and objective facts do not match. Specific derivation method, F $=$ GMm / R2 $=$ mg, g $=$ GM / R2 . ¢Ù, G is the gravitational constant, M is the mass of the earth, and finally the g $=$ 9.8 m / s 2 is obtained. We assume that the earth is a standard positive sphere, the earth's volume V $=$ 4$\Pi $R3 / 3, assuming that the earth's density is $\rho $, then M $= \quad \rho $4$\Pi $R3 / 3 ..¢Ú, the ¢Ú into ¢Ù get: g $=$ G$\rho $4$\Pi $R / 3 ..¢Û, the density of the earth is constant. Careful analysis of the formula ¢Û The result of this calculation, we can reach conclusion the gravity acceleration g and the radius of the earth is proportional. In addition to the radius of the Earth ¢Û the right is constant, That is, the Earth's Gravity acceleration of the outer layer of the earth is greater than the Earth's Gravity acceleration of Inner layer. We are in High School, Huairou District, Beijing, China Author: hanyongquan tangyuteng TEL: 15611860790, 15810953809 [Preview Abstract] |
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BP11.00003: Reverse Current Shock Induced by Plasma-Neutral Collision Pakorn Wongwaitayakornkul, Magnus Haw, Hui Li, Shengtai Li, Paul Bellan The Caltech solar experiment creates an arched plasma-filled flux rope expanding into low density background plasma. A layer of electrical current flowing in the opposite direction with respect to the flux rope current is induced in the background plasma just ahead of the flux rope. Two dimensional spatial and temporal measurements by a 3-dimensional magnetic vector probe demonstrate the existence of this induced current layer forming ahead of the flux rope. The induced current magnitude is 20$\%$ of the magnitude of the current in the flux rope. The reverse current in the low density background plasma is thought to be a diamagnetic response that shields out the magnetic field ahead of the propagation. The spatial and magnetic characteristics of the reverse current layer are consistent with similar shock structures seen in 3-dimensional ideal MHD numerical simulations performed on the Turquoise supercomputer cluster using the Los Alamos COMPutational Astrophysics Simulation Suite. This discovery of the induced diamagnetic current provides useful insights for space and solar plasma. [Preview Abstract] |
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BP11.00004: From Scatter-Free to Diffusive Propagation of Energetic Particles: Exact Solution of Fokker-Planck equation Mikhail Malkov Propagation of energetic particles through magnetized turbulent media is reconsidered using the exact solution of Fokker-Planck equation [PRD, 2017]. It shows that the cosmic ray (CR) transport in weakly scattering media is nondiffusive. Poor understanding of the CR transport obscures their sources and acceleration mechanisms. We present a simplified approximate version of the exact solution of Fokker-Planck equation that accurately describes a ballistic, diffusive and transdiffusive (intermediate between the first two) propagation regimes. The transdiffusive phase lasts up to 5-7 collision times and starts at about one-half of collision time. Since the scattering rate is energy-dependent, a large part of the energy spectrum propagates neither diffusively nor ballistically. Its treatment should rely on the exact solution. Significant parts of the spectra affected by the heliospheric modulation, for example, falls into this category. We present a new approximation of an exact Fokker-Planck propagator. It conveniently unifies the ballistic and Gaussian propagators, currently used (separately) in major Solar modulation and other CR transport models. The maximum deviation of the new propagator from the exact solution is less than a few percents. [Preview Abstract] |
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BP11.00005: Cygnus Code Simulation of Magnetoshell Aerocapture and Entry System Akihisa Shimazu, David Kirtley, Dan Barnes, John Slough A Magnetoshell Aerocapture and Entry System (MAC) [1] is a novel concept for planetary atmospheric entry, which enables both manned and planetary deep space orbiter space missions that are difficult with present day technologies. The MAC uses a low-beta dipole plasma magnetoshell to produce a drag effect on the spacecraft through the collisional interactions between the entry atmospheric neutrals and the confined plasma in the magnetoshell, creating a dynamic and controllable plasma parachute for entry. To understand the performance and the behavior of the MAC, the Cygnus 2D Hall MHD code is used for this study. The Cygnus code is a 2D Hall MHD code with coupled external circuits, which has been originally developed for studying FRC formation, translation, merging, and compression. In this study, the Cygnus code is modified to support the MAC geometry with a simplified plasma-neutral model that accounts for electron-impact ionization, radiative recombination, and resonant charge exchange to simulate the collisional interaction processes for the MAC. [1] D. Kirtley et al. ``A Plasma Aerocapture and Entry System for Manned Missions and Planetary Deep Space Orbiters'', NASA NIAC Phase I Final Report, NNX12AR12G. [Preview Abstract] |
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BP11.00006: 3D3V hybrid-kinetic simulations with electron inertia effects of kinetic-range solar-wind turbulence Silvio Sergio Cerri, Sergio Servidio, Francesco Califano Characterizing the nature of the turbulent fluctuations below the ion gyroradius in solar-wind turbulence and its dependence on the plasma parameters is a great challenge. Here we present a study of the sub-proton-scale cascade based on high-resolution hybrid-Vlasov (Eulerian) simulations of freely-decaying turbulence in 3D3V phase space, including finite electron inertia effects. Two proton plasma beta regimes are explored: $\beta_p=1$ and $\beta_p=0.2$ ($\beta$ is the ratio between thermal and magnetic pressures). At $\beta_p=1$, the magnetic energy spectum exhibit $k_\perp^{-8/3}$ and $k_\|^{-7/2}$ power laws, while they are slightly steeper for $\beta_p=0.2$. Nevertheless, both regimes develop a spectral anisotropy consistent with $k_\|\sim k_\perp^{2/3}$ at $k_\perp\rho_p>1$, and small-scale intermittency (the $\beta_p=0.2$ case being slightly more intermittent than the $\beta_p=1$ counterpart). In this context, we find that kinetic-range turbulence is consistent with a cascade of kinetic Alfv\'en waves type of fluctuations at $\beta_p=1$, whereas the low-$\beta$ case presents a more complex scenario suggesting the simultaneous presence of several type of fluctuations. [Preview Abstract] |
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BP11.00007: Energy Dissipation and Phase-Space Dynamics in Eulerian Vlasov-Maxwell Turbulence Jason TenBarge, James Juno, Ammar Hakim Turbulence in a magnetized plasma is a primary mechanism responsible for transforming energy at large injection scales into small-scale motions, which are ultimately dissipated as heat in systems such as the solar corona, wind, and other astrophysical objects. At large scales, the turbulence is well described by fluid models of the plasma; however, understanding the processes responsible for heating a weakly collisional plasma such as the solar wind requires a kinetic description. We present a fully kinetic Eulerian Vlasov-Maxwell study of turbulence using the Gkeyll simulation framework, including studies of the cascade of energy in phase space and formation and dissipation of coherent structures. We also leverage the recently developed field-particle correlations to diagnose the dominant sources of dissipation and compare the results of the field-particle correlation to other dissipation measures. [Preview Abstract] |
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BP11.00008: A Grad-Shafranov Model of Solar Equilibrium Lee Gunderson, Amitava Bhattacharjee Helioseismology has revealed the internal density and rotation profile of the sun. However, knowledge of its magnetic fields and meridional circulation is confined much closer to the surface, and latitudinal variations in entropy are below detectable limits. Numerical simulations can offer insight into the interior dynamics, and help identify which ingredients are necessary to produce particular features. However, several gross features of the Sun can be understood from an equilibrium perspective, for example the 1-D density profile arising from steady-state energy transport from the core to the surface, or the tilting of rotation contours in the convection zone due to baroclinic forcing. To help answer the question of which features can be qualitatively explained by equilibrium, we propose analyzing stationary axisymmetric ideal MHD flows (i.e. the Grad-Shafranov equation) in the solar regime. We compare our model to that of Balbus (2009), recovering a similar rotation profile in bulk of the convection zone. Furthermore, it includes the effects of poloidal flow, developing a feature reminiscent of the near surface shear layer. [Preview Abstract] |
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BP11.00009: Development of a Rotating Magnetized Plasma Device David Cooke, James Patton, Remington Reid, Ashley Stiles, Patrik Morrison, Andrei Koch Momentum coupling in plasma is a mechanism that is central to a wide range of interesting and important phenomena, magnetosphere-ionosphere coupling, solar eruptions, the interaction of an electro-dynamic tether system in the Earth's ionosphere, and the Critical Ionization Velocity (CIV) mechanism are a few examples. One result of the Space Shuttle Tethered Satellite experiment, TSS-1R, was that the current-voltage response of the experiment in all orbit conditions fell into a narrow range of curves when parameterized as a plasma probe [Thompson, GRL,1998]. Another striking result was the lack of dependence on the Alfv\'{e}n velocity or other electro-magnetic parameters. This result has led us to revisit the understanding of the speed with which an electric field propagates along the magnetic field using EM-PIC simulation and experiments in our new magnetized plasma chamber. Our initial experiment is a rotating plasma using a solenoidal magnetic field and a radial electric field, with pulsed differential rotation of the plasma column to study the strength of coupling and propagation speed. Characteristics of our `first light' rotating plasma will be presented. [Preview Abstract] |
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BP11.00010: Laser Induced Fluorescence for Singly Ionized Atomic Iodine Thomas Steinberger, Earl Scime While xenon is the standard propellant for a wide range of plasma thrusters, xenon is expensive and xenon propellant systems require heavy compressed gas tanks, pressure regulators, and other bulky hardware. Iodine has similar mass and is much easier to acquire than xenon. Iodines natural state of matter at room temperature is solid and is easily sublimated to gas with a simple heating element. This advantage for iodine is also a significant challenge when developing gas handling systems for iodine. Another challenge for iodine thrusters is a lack of well-defined spectroscopic diagnostics for single ionized iodine, specifically, a lack of a demonstrated laser induced fluorescence (LIF) scheme. We present emission spectroscopy measurements of iodine ion emission from the $6p^5P_3-5d^5D^o_4$ transition at $695.878$ nm and the $6p^5P_3-6s^5S^o_2$ transition at $516.12$ nm as a function of pressure and microwave power for a microwave excited iodine plasma in a sealed quartz cell at a pressure of 1 mTorr. The $5d^5D^o_4$ state is metastable and was identified by Hargus et al. [48th AIAA Joint Propulsion, 2012] as a strong candidate for an iodine ion LIF scheme. We will also present preliminary LIF measurements using a tunable dye laser operating at $695.878$ nm. [Preview Abstract] |
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BP11.00011: X-ray observations from RT-1 magnetospheric plasmas Tetsuya Sugata Planetary magnetospheres like Earth and Jupiter realize stable confinement of high beta plasma. The RT-1 device produces a laboratory magnetosphere by using a levitated superconducting coil for dipole magnetic fields and 8.2 GHz electromagnetic wave for plasma production ($n_e \sim 10^{17} {\bf m}^{-3}$) and electron heating. In the recent experiments, the RT-1 device has achieved the local beta that exceeds 1. It is considered that the high energy component of electrons contributes to the beta value. Therefore, Si(Li) detectors measured the X-ray spectra from the peripheral plasmas in the range from a few keV to a few ten keV. The density of a few keV component and a few ten keV component are comparable and a few ten keV component dominates the majority of the high beta value that is operated up to 0.8. We found that 150 keV component of electrons exists near the outer of the levitated dipole magnet by using a CdTe detector. [Preview Abstract] |
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BP11.00012: Magnetic Diagnosis Upgrade and Analysis for MHD Instabilities on the J-TEXT Daojing Guo, Qiming Hu, Ge Zhuang, Nengchao Wang, Yonghua Ding, Yuejin Tang, Qingquan Yu The magnetic diagnostic system on the J-TEXT tokamak has been upgraded to measure the magnetohydrodynamic (MHD) instabilities with diverse bands of frequencies. 12 saddle loop probes and 73 Mirnov probes are newly developed. The fabrication and installment of the new probes are elaborately designed, in consideration of higher spatial resolution and better amplitude-frequency characteristic. In this case, the probes utilize two kinds of novel fabrication craft, one of which is low temperature co-fired ceramics (LTCC), the other is flexible printed circuit (FPC). A great deal of experiments on the J-TEXT have validated the stability of the new system. Some typical discharges observed by the new diagnostic system are reviewed. In order to extract useful information from raw signals, several efficient signal processing methods are reviewed. An analytical model based on lumped eddy current circuits is used to compensate equilibrium flux and the corresponding eddy current fluxes, a visualization processing based on singular value decomposition (SVD) and cross-power spectrum are applied to detect the mode number. [Preview Abstract] |
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BP11.00013: Structure-preserving geometric algorithms for plasma physics and beam physics Hong Qin Standard algorithms in the plasma physics and beam physics do not possess the long-term accuracy and fidelity required in the study of multi-scale dynamics, because they do not preserve the geometric structures of the physical systems, such as the local energy-momentum conservation, symplectic structure and gauge symmetry. As a result, numerical errors accumulate coherently with time and long-term simulation results are not reliable. To overcome this difficulty, since 2008 structure-preserving geometric algorithms have been developed [1-11]. This new generation of algorithms utilizes advanced techniques, such as interpolating differential forms [3,5], canonical [7] and non-canonical [5,6] symplectic integrators, and finite element exterior calculus [8] to guarantee gauge symmetry and charge conservation[3,5], and the conservation of energy-momentum [3,4,5-11] and symplectic structure [1,3,4,5-11]. It is our vision that future numerical capabilities in plasma physics and beam physics will be based on the structure-preserving geometric algorithms. Refs.: [1]H. Qin et al., PRL 100, 035006 (2008). [2]H. Qin et al., PoP 20, 084503 (2013). [3]J. Squire et al., PoP~19, 084501 (2012). [4]J. Xiao et al., PoP 20, 102517 (2013). [5]Y. Zhou et al., PoP 21, 102109 (2014). [6]J. Xiao et al., PoP 22, 112504 (2015). [7]Y. He et al., PoP 22,124503 (2015). [8]H. Qin et al., NF 56, 014001 (2016). [9]Y. He, et al., PoP 23, 092108, (2016). [10]J. Xiao et al., PoP 23, 112107 (2016). [11] J.Xiao et al., PoP 24, 062112 (2017). [Preview Abstract] |
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BP11.00014: Comparisons and applications of four independent numerical approaches for linear gyrokinetic drift modes Ou Weike, Huasheng Xie, Yueyan Li, Zhixin Lu, Bo Li To help reveal the complete picture of linear kinetic drift modes, four independent numerical approaches, based on the integral equation, Euler initial value simulation, Euler matrix eigenvalue solution, and Lagrangian particle simulation, respectively, are used to solve the linear gyrokinetic electrostatic drift mode equation in Z-pinch with slab simplification and in tokamak with a ballooning space coordinate. We identify that these approaches can yield the same solution with the difference smaller than 1{\%}, and the discrepancies mainly come from the numerical convergence, which is the first detailed benchmark of four independent numerical approaches for gyrokinetic linear drift modes. Using these approaches, we find that the entropy mode and interchange mode are on the same branch in Z-pinch, and the entropy mode can have both electron and ion branches. And, at a strong gradient, more than one eigenstate of the ion temperature gradient mode (ITG) can be unstable and the most unstable one can be on non-ground eigenstates. The propagation of ITGs from ion to electron diamagnetic direction at strong gradient is also observed, which implies that the propagation direction is not a decisive criterion for the experimental diagnosis of turbulent mode at the edge plasmas. Huasheng Xie, \textit{et al.}, Phys. Plasmas \textbf{24}, 072106(2017) [Preview Abstract] |
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BP11.00015: Kinetic Simulations -- Oshun (Vlasov-Fokker-Planck) and PIC (Osiris) -- Physics and Open Source Software In The UCLA PICKSE Initiative. Adam Tableman, Michail Tzoufras, Ricardo Fonseca, W.B. Mori We present physics results and general updates for two plasma kinetic simulation codes developed under the UCLA PICKSE initiative. We also discuss the issues around making these codes open source such that they can be used (and contributed too) by a large audience. The first code discussed is Oshun -- a Vlasov-Fokker-Planck (VFP) code. Recent simulations with the VFP code OSHUN [1] will be presented for all of the aforementioned problems. The algorithmic improvements that have facilitated these studies will be also be discussed. [1] M. Tzoufras, A.R. Bell, P.A. Norreys, F.S. Tsung, JCP 230 (17), 6475-6494 (2011); M. Tzoufras, A. Tableman, F.S. Tsung, W.B. Mori, A.R. Bell, Phys. Plasmas 20, 056303 (2013) The second code discussed is the PIC code Osiris. Osiris is a widely respected code used in hundreds of papers. Osiris was first developed for laser-plasma interactions but has grown into a robust framework covering most areas of plasma research. One defining feature of Osiris is that it is highly optimized for a variety of hardware configurations and scales linearly over 1 million$+$ CPU nodes. We will discuss the recently released version 4.0 written in modern, fully-object oriented FORTRAN. [Preview Abstract] |
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BP11.00016: Validation of a Magnetized Liner Inertial Fusion (MagLIF) hotspot model to determine primary stagnation parameters. Matthew Evans, Patrick Knapp, Michael Glinsky, Stephaine Hansen, Matt Gomez, Chris Jennings, Taisuke Nagayama, Pierre Gourdain, Brent Jones A simplified 2D model of a MagLIF[1] hotspot at stagnation along with a Bayesian inference network is used to determine experimental stagnation parameters. The hotspot model is described by a series of 1-D isobaric cylindrical slices, each with six parameters: pressure, temperature, mix fraction, mix charge, radius, and linear areal density. The model is then fed into the Bayesian inference network which uses a Levenberg-Marquardt algorithm to performs non-linear least squares fit, then uses a Markov chain Monte Carlo (MCMC) to improve performance. Validation of the model is performed in two parts. First by performing the inversion using synthetic data generated by the model against itself. Next, simulation data generated by GORGON[2] is post processed to create synthetic diagnostics which are used in the inversion and compared to original states. Correlations among model parameters and diagnostics data and their implications for inferring model parameters are discussed. [Preview Abstract] |
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BP11.00017: Method for determining k-vector of a wave by a single spacecraft Paul Bellan A practical method\footnote{% P. M. Bellan, JGR-Space Phys. 121, 8589 (2016).} is described for determining the 3D wave-vector of quasi-neutral plasma waves using magnetic field and electric current density measurements made by a single spacecraft. This wave-vector knowledge can then be used to remove the space-time ambiguity produced by frequency Doppler shift associated with spacecraft motion so the actual plasma-frame wave dispersion relation is determined with no theoretical assumptions. The method involves applying the Wiener-Khinchin theorem to cross-correlations of the current and magnetic field oscillations and to auto-correlations of the magnetic field oscillations; the wave-vector is proportional to the ratio of the Fourier transforms of these cross- and auto-correlations. The method requires that each wave frequency component map to a unique wave-vector, a situation presumed true in many spacecraft measurement situations. Synthetic data examples that validate the method are presented. The method has recently been used successfully on data from the MMS spacecraft\footnote{% D. Gershman et al., Nature Comm. 8, 14719 (2017).}. [Preview Abstract] |
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BP11.00018: New Magnetic Field Topologies and Amplification by Local Depletion of Electron Thermal Energy A. Fletcher, B. Coppi The conventional theory of magnetic reconnection by the tearing mode in weakly collisional and collisionless plasmas involve characteristic length scales that are unrealistically small for space plasmas. This fact motivates the search for modes that produce magnetic reconnection over microscopic scale distances that remain significant when large macroscopic scale distances are considered. Modes that, depend on the existence of a significant electron temperature gradient can have this desired property [1]. A neutral sheet configuration is considered as in the case of Ref. [2] where auroral substorms have been proposed, for the first time, to result from magnetic reconnection processes occurring in the Earth’s magnetotail. Now a new kind of mode that is localized within the region where reconnection takes place is found with an exact analytical solution of the equation describing the reconnected field. The topology of this is different from that of the well known drift-tearing type of modes and consists of two parallel strings of magnetic islands.\\ [1] B. Coppi, Plasma Physics Reports, $\bf{42}$, No. 5, 383 (2016).\\ [2] B. Coppi, G. Laval and R. Pellat, Phys. Rev. Letter, $\bf{16}$, 1207 (1966). [Preview Abstract] |
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BP11.00019: Particle transport characteristics of the RT-1 magnetospheric plasma using gas-puffing modulation technique Naoki Kenmochi, Masaki Nishiura, Zensho Yoshida, Tetsuya Sugata, Kaori Nakamura, Shotaro Katsura The Ring Trap 1 (RT-1) device creates a laboratory magnetosphere that is realized by a levitated superconducting ring magnet in vacuum. The RT-1 experiment has demonstrated the self-organization of a plasma clump with a steep density gradient; a peaked density distribution is spontaneously created through ‘inward diffusion’. In order to evaluate particle transport characteristics in the RT-1 magnetospheric plasmas which cause these inward diffusion, density modulation experiments were performed in the RT-1. Density modulation is a powerful method for estimating a diffusion coefficient D and a convection velocity V by puffing a periodic neutral gas. The gas puff modulation causes the change in the electron density measured by two chords of microwave interferometer (the radial positions r = 60 and 70 cm, vertical chord). In the case of 2 Hz gas puff modulation, the phase delay and the modulation-amplitude decay at the chord r = 60 cm are obtained with 15 degree and 0.8, respectively, with respect to the phase and the amplitude at r = 70 cm. The particle balance equations are solved on the assumption of profile shapes for D to evaluate D, V and particle source rate. The result suggests the inward convection in high beta magnetospheric plasmas. [Preview Abstract] |
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BP11.00020: Lunar mini-magnetospheres as electron scale plasma laboratories RA Bamford, B Kellett, R Bingham, EP Alves, F Cruz, LO Silva Space offers few opportunities to make measurements under consistent conditions such as can be provided in the laboratory. Visible from Earth, the spectacular Reiner Gamma Formation, is the quintessential example of a lunar swirl - anomalous white wispy markings on the moons surface - that represents an integrated record of differential solar proton bombardment. The surface magnetic fields are 500 nT at most and the overall size of the magnetic anomalies (100s of km) is of the order or less than the ion gyro-radius, and yet mini-magnetospheres, with miniature collisionless shocks, have been observed by spacecraft. The fixed location and footprint of magnetic fields provides almost laboratory like conditions. The data collected by a number of lunar survey missions since the 1960’s reflect this making them ideal objects to study at the fundamental electron scale. Theory and particle in cell simulations of these mini magnetosphere structures provide confirmation of the need to involve electron-scale dynamics. [Preview Abstract] |
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BP11.00021: Two-fluid studies including pressure tensor effects of current sheet instabilities and reconnection in the magnetotail Jonathan Ng, A Hakim, A Bhattacharjee The ballooning instability is a possible mechanism leading to the triggering of magnetic substorms and this is supported by observations of fluctuations in the ballooning frequency range in the Earth’s magnetotail [1,2]. Kinetic and MHD studies of generalised current sheets have shown how these instabilities can develop and affect dynamics of substorms by driving flows and causing the formation of plasmoids [3, 4]. Using a two-fluid model which includes pressure tensor effects, we first perform a study of current sheet instabilities and show that the ion pressure tensor is necessary for agreement with kinetic models. We then perform 3D simulations of magnetotail configurations to study the coupling between the ballooning instability and magnetic reconnection and the possible effects on substorm onset. Qualitative comparisons with THEMIS and MMS observations will be made.\ [1] L.-J. Chen et al. GRL (2003) [2] E. A. Panov et al. JGR (2012) [3] P. L. Pritchett & F. V. Coroniti JGR (2013) [4] P. Zhu et al. Phys. Plasmas (2017) [Preview Abstract] |
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BP11.00022: Magnetic Reconnection in Filaments and Solar Coronal Loops M. Asgari-Targhi, B. Coppi, B. Basu, A. Fletcher, L. Golub We propose that a magneto-thermal reconnection process is relevant to the physics of solar coronal loops. In this adopted model, magnetic reconnection is associated with electron temperature gradients, anisotropic electron temperature fluctuations and plasma current density gradients. Based on this model, we show that magnetic energy can be converted into electron thermal energy and (heating the corona [1]) and high energy particle populations. The input parameters for our model are based on the observations of the corona from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). We compare the results of our modeling with measurements of temperature, density and energy from relevant observations.\\ 1. Beaufum$\acute{e}$, B. Coppi and L. Golub, $\it{Ap J}. \bf{393}$, 396 (1992). [Preview Abstract] |
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BP11.00023: Numerical modeling of the thin shallow solar dynamo J.B. O'Bryan, T.R. Jarboe Nonlinear, numerical computation with the NIMROD code is used to explore and validate the thin shallow solar dynamo model [T.R. Jarboe et. al. 2017], which explains the observed global temporal evolution (e.g. magnetic field reversal) and local surface structures (e.g. sunspots) of the sun. The key feature of this model is the presence and magnetic self-organization of global magnetic structures (GMS) lying just below the surface of the sun, which resemble 1D radial Taylor states of size comparable to the supergranule convection cells. First, we seek to validate the thin shallow solar dynamo model by reproducing the \textasciitilde 11 year timescale for reversal of the solar magnetic field. Then, we seek to model formation of GMS from convection zone turbulence. Our computations simulate a slab covering a radial depth \textasciitilde 3Mm and include differential rotation and gravity. Density, temperature, and resistivity profiles are taken from the Christensen-Dalsgaard model. [Preview Abstract] |
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BP11.00024: On self-organization of the solar magnetic fields Thomas Jarboe, Thomas Benedett, Kyle Morgan Recent advances in self-organization effects of magnetized plasma are shown to have a powerful effect in the Sun. The resulting model consists of a thin, magnetic equilibrium covering most of the solar surface below the photosphere, within the supergranules. The equilibrium is reshaped and reorganized on an 11-year half-cycle perhaps due to resistive diffusion. The thinness of the equilibrium makes the solar dynamo powerful enough to also fuel other solar phenomena, such as the chromosphere, the corona, the solar wind, and the current in the solar current sheet. It also explains the 180 degree flipping of the magnetic fields and the pattern of the radial magnetic field in the solar cycle, the flipping of the polar magnetic flux, the nature of sunspots and CMEs, the differences of the corona during solar minimum compared to solar maximum, the amplitude of torsional oscillations, the nature of supergranules and the plasma structure in solar prominences. [Preview Abstract] |
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BP11.00025: Anomalies in Cosmic Ray Composition: Explanation Based on Mass to Charge Ratio Adrian Hanusch, Tatiana Liseykina, Mikhail Malkov Observations of galactic cosmic rays (CR) revealed the lack of our understanding of how CR elements are extracted from the supernova environments to be further accelerated in their shocks. Comparing the spectra of accelerated particles with different mass to charge ratios is a powerful tool for studying the physics of particle injection into the diffusive shock acceleration (DSA). Recent AMS-02 demonstration of the similarity of He/p, C/p and O/p rigidity spectra provide new evidence that injection is a mass-to-charge (A/Z) dependent process. We performed hybrid simulations of collisionless shocks and analyzed a joint injection of $p$ and He$^{2+}$ in conjunction with upstream waves they generate. Our results equally apply to C and O fully ionized ions, since they have similar A/Z values. By convolving the time-dependent injection rates of $p$ and He, obtained from the simulations, with a decreasing shock strength over the active life of SNRs, we generate the integrated SNR spectra for $p$ and He. These spectra are consistent with the AMS-02 and Pamela data and earlier theoretical predictions. Our interpretation of the elemental anomaly is therefore intrinsic to collisionless shock mechanisms and does not require contributions from several different SNRs. [Preview Abstract] |
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BP11.00026: Charge conserving current deposition scheme for PIC simulations in modified spherical coordinates F. Cruz, T. Grismayer, R.A. Fonseca, L.O. Silva Global models of pulsar magnetospheres have been actively pursued in recent years. Both macro and microscopic (PIC) descriptions have been used, showing that collective processes of e-e$+$ plasmas dominate the global structure of pulsar magnetospheres. Since these systems are best described in spherical coordinates, the algorithms used in cartesian simulations must be generalized. A problem of particular interest is that of charge conservation in PIC simulations. The complex geometry and irregular grids used to improve the efficiency of these algorithms represent major challenges in the design of a charge conserving scheme. Here we present a new first-order current deposition scheme for a 2D axisymmetric, log-spaced radial grid, that rigorously conserves charge. We benchmark this scheme in different scenarios, by integrating it with a spherical Yee scheme and Boris/Vay pushers. The results show that charge is conserved to machine precision, making it unnecessary to correct the electric field to guarantee charge conservation. This scheme will be particularly important for future studies aiming to bridge the microscopic physical processes of e-e$+$ plasma generation due to QED cascades, its self-consistent acceleration and radiative losses to the global dynamics of pulsar magnetospheres. [Preview Abstract] |
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BP11.00027: Development of a hybrid gyrokinetic ion and isothermal electron fluid code and its application to turbulent heating in astrophysical plasma Yohei Kawazura, Michael Barnes Understanding the ion-to-electron temperature ratio is crucial for advancing our knowledge in astrophysics. Among the possible thermalization mechanisms, we focus on the dissipation of Alfv\'{e}nic turbulence. Although several theoretical studies based on linear Alfv\'{e}n wave damping have estimated the dependence of heating ratio on plasma parameters, there have been no direct nonlinear simulation that has investigated the heating ratio scanning plasma parameters. Schekochihin et al. (2009) proved that the turbulent heating ratio is determined at the ion Lamor radius scale. Therefore, we do not need to resolve all the scales up to the electron dissipation scale. To investigate the ion kinetic scale effectively, we developed a new code that solves a hybrid model composed of gyrokinetic ions and an isothermal electron fluid (ITEF). The code is developed by incorporating the ITEF approximation into the gyrokinetics code \texttt{AstroGK} (Numata et al., 2010). Since electron kinetic effects are eliminated, the new hybrid code runs approximately $2\sqrt{m_i/m_e}$ times faster than full gyrokinetics codes. We will present linear and nonlinear benchmark tests of the new code and our first result of the heating ratio sweeping the plasma beta and ion-to-electron temperature ratio. [Preview Abstract] |
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BP11.00028: Simulations of a Molecular Cloud experiment using CRASH Matthew Trantham, Paul Keiter, Robert Vandervort, R. Paul Drake, Dov Shvarts Recent laboratory experiments explore molecular cloud radiation hydrodynamics. The experiment irradiates a gold foil with a laser producing x-rays to drive the implosion or explosion of a foam ball. The CRASH code, an Eulerian code with block-adaptive mesh refinement, multigroup diffusive radiation transport, and electron heat conduction developed at the University of Michigan to design and analyze high-energy-density experiments, is used to perform a parameter search in order to identify optically thick, optically thin and transition regimes suitable for these experiments. Specific design issues addressed by the simulations are the x-ray drive temperature, foam density, distance from the x-ray source to the ball, as well as other complicating issues such as the positioning of the stalk holding the foam ball. We present the results of this study and show ways the simulations helped improve the quality of the experiment. [Preview Abstract] |
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BP11.00029: Abstract Withdrawn
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(Author Not Attending)
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BP11.00030: Compton scattering collision module for OSIRIS Fabrizio Del Gaudio, Thomas Grismayer, Ricardo Fonseca, Luís Silva Compton scattering plays a fundamental role in a variety of different astrophysical environments, such as at the gaps of pulsars and the stagnation surface of black holes. In these scenarios, Compton scattering is coupled with self-consistent mechanisms such as pair cascades. We present the implementation of a novel module, embedded in the self-consistent framework of the PIC code OSIRIS 4.0, capable of simulating Compton scattering from first principles and that is fully integrated with the self-consistent plasma dynamics. The algorithm accounts for the stochastic nature of Compton scattering reproducing without approximations the exchange of energy between photons and unbound charged species. We present benchmarks of the code against the analytical results of Blumenthal et al. and the numerical solution of the linear Kompaneets equation and good agreement is found between the simulations and the theoretical models. [Preview Abstract] |
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BP11.00031: Modification of the Magnetized Shercliff Layer Instability in the Princeton MRI Experiment by Conducting Endcaps Kyle Caspary, Dahan Choi, Erik Gilson, Jeremy Goodman, Hantao Ji, Peter Sloboda The Princeton MRI experiment is a modified Taylor-Couette device that uses a GaInSn eutectic working fluid to study rotating MHD flows. Results are presented from an experimental and numerical study investigating the effect of conducting axial boundary conditions, as opposed to insulating boundaries, on a free-Shercliff-layer instability. The free Shercliff layer is formed when a sufficiently strong magnetic field is imposed across a rotating, conducting fluid that is bounded axially by end caps with a pair of differentially rotating rings. With insulating end caps, the instability threshold corresponds to when the Elsasser number equals unity and the instability is characterized by a transition from flows with azimuthal structure with mode number m > 1 to flows with a dominant m = 1 mode. A reduced stability threshold is observed for a variety of sheared flows with the introduction of conducting end caps. In this case, the stability threshold is well-described by an Elsasser number of unity but using the conductivity and density of copper and the instability is characterized by fluctuations in multiple m > 1 modes. Measurements of the fluid velocity field are compared with results from the Spectral Finite Element Maxwell and Navier Stokes (SFEMaNS) code. [Preview Abstract] |
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BP11.00032: The Role of Kinetic Instabilities in the Collisionless Turbulent Dynamo D. A. St-Onge, M. W. Kunz Conservation of the first adiabatic invariant $\mu$ in a magnetized, collisionless plasma precludes turbulent amplification of the magnetic field. This is because any increase in magnetic-field strength would adiabatically increase the perpendicular pressure, whose growth is stringently limited by the finite free energy in the system. A mechanism is then needed to break $\mu$ conservation in order to enable the amplification of a weak, primordial seed magnetic field to dynamically important strengths. Conveniently, amplification of the magnetic field in a high-beta plasma leads to pressure anisotropies large enough to trigger kinetic instabilities at ion-Larmor scales (e.g., firehose, mirror). These instabilities saturate by causing anomalous scattering of particles, breaking $\mu$ conservation. This interplay between magnetic-field growth and kinetic instabilities adds a new layer of complexity to the more conventional (and much better understood) magnetohydrodynamic turbulent dynamo. Using self-consistent hybrid-kinetic, particle-in-cell simulations, we investigate the impact of these kinetic instabilities on the turbulent dynamo in a collisionless plasma, with a particular focus on how kinetic effects enable the amplification of magnetic fields and modify their structure. [Preview Abstract] |
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BP11.00033: Precursor Events Involving Plasmas Structures\\ Around Collapsing Black Holes Binaries M. Medvedev, B. Coppi The plasma structures that can exist around black hole binaries can sustain intrinsic plasma collective modes [1] that have characteristic low frequencies related to the particle rotation frequencies around the binary system. As the collapse approaches, with the loss of angular momentum by emission of gravitational waves [2] from the binary system we have suggested [3] that the frequency of the fluctuating component of the gravitational potential can go through that of the intrinsic modes of the surrounding plasma structure and lead to a sharp amplification of them. Then the precursor to the event reported in Ref. [2], tentatively identified by the Agile X-$\gamma$-ray observatory [4] may be associated with the high energy radiation emission due to the fields produced by excitation of the proposed plasma modes. M. Tavani is thanked for bringing Ref. [4] to our attention while Ref. [3] was being completed.\\ [1] B. Coppi, Plasma Physics Report, 43, 3, 289–297 (2017).\\ [2] B. Abbot, R. Abbot, T. Abbot et al. Phys. Rev. Lett. 118, 221101 (2017).\\ [3] B. Coppi and M. Medvedev, MIT-LNS HEP 17/02 June 2016. To be submitted to Physics Letters.\\ [4] F. Verrecchia, M. Tavani, A. Ursi, et al., to be published in Ap.J. Letters. [Preview Abstract] |
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BP11.00034: Progress Towards High-Speed Operation of the Magnetorotational Instability Experiment and Diagnostic Development E. P. Gilson, K. Caspary, D. Choi, F. Ebrahimi, J. Goodman, H. Ji, M. Lysandrou, P. Sloboda, M. Tabbutt Estimates and simulations both suggest that the Princeton MRI experiment must operate with inner cylinder rotation rates $>$ 1,500 rpm, corresponding to magnetic Reynolds numbers $Rm > 3$, in order for the flow to be unstable to the MRI. Results will be presented demonstrating progress towards high-speed operation while avoiding adverse effects from large dynamic pressure and heat. Recent studies show that conductive end caps increase the magnitude of the saturated MRI signal, enabling easier detection [1]. However, motor control feedback and pneumatically-driven brakes must be used to maintain control when forces arise from the interaction between induced currents in the rotating end caps and the 3,000 G applied magnetic field. The use of Hall probes and strain gauges to measure the azimuthal magnetic field and the torque at the inner cylinder will be discussed. Results from the Spectral Finite Element and Navier Stokes code have been used to better understand the expected shape of the MRI threshold curve with conducting end caps, the nature of the forces on the end caps, and to predict the magnetic fields and torques at the inner cylinder that result from the onset of the MRI.\newline [1] X. Wei, et al., Phys. Rev. E \textbf{94}, 063107 (2016). [Preview Abstract] |
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BP11.00035: Electron-Positron Cascade in Magnetospheres of Spinning Black Holes Alex L. Ford, Brett D. Keenan, Mikhail V. Medvedev We quantitatively study the stationary, axisymmetric, force-free magnetospheres of spinning (Kerr) black holes (BHs) and the conditions needed for relativistic jets to be powered by the Blandford-Znajek mechanism. These jets could be from active galactic nuclei, blazars, quasars, micro-quasars, radio active galaxies, and other systems that host Kerr BHs. The structure of the magnetosphere determines how the BH energy is extracted, e.g., via Blandford-Znajek mechanism, which converts the BH rotational energy into Poynting flux. The key assumption is the force-free condition, which requires the presence of plasma with the density being above the Goldreich-Julian density. Unlike neutron stars, which in principle can supply electrons from the surface, BH cannot supply plasma at all. The plasma must be generated in situ via an electron-positron cascade, presumably in the gap region. Here we study varying conditions that provide a sufficient amount of plasma for the Blandford-Znajek mechanism to work effectively. [Preview Abstract] |
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BP11.00036: New Mexico Liquid Metal $\alpha\omega$-dynamo experiment: Most Recent Progress Jiahe Si, Richard Sonnenfeld, Art Colgate, Hui Li The goal of the New Mexico Liquid Metal $\alpha\omega$-dynamo experiment is to demonstrate a galactic dynamo can be generated through two phases, the $\omega$-phase and $\alpha$-phase by two semi-coherent flows in laboratory. We have demonstrated an 8-fold poloidal-to-toroidal flux amplification from differential rotation (the $\omega$-effect) by minimizing turbulence in our apparatus. To demonstrate the $\alpha$-effect, major upgrades are needed. The upgrades include building a helicity injection facility, mounting new 100hp motors and new sensors, designing a new data acquisition system capable of transmitting data from about 80 sensors in a high speed rotating frame with an overall 200kS/sec sampling rate. We hope the upgrade can be utilized to answer the question of whether a self-sustaining $\alpha\omega$-dynamo can be implemented with a realistic lab fluid flow field, as well as to obtain more details to understand dynamo action in highly turbulent Couette flow. [Preview Abstract] |
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BP11.00037: 2D MRI-induced turbulence in high $\beta$ PIC simulation Giannandrea Inchingolo, Thomas Grismayer, Nuno F. Loureiro, Ricardo A. Fonseca, Luis O. Silva The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical scenarios, as accretion disks nearness neutron stars and black holes. The MRI has been widely studied using MHD models and simulations, in order to understand the behaviour of astrophysical fluids in a state of differential rotation. When the timescale for electron and ion collisions is longer than the inflow time in the disk, the plasma is macroscopically collisionless and MHD breaks down. This is the case of the limit of weak magnetic field, i.e., as the ratio of the ion cyclotron frequency to orbital frequency becomes small. Leveraging on the recent addition of the shearing co-rotating frames equations of motion and Maxwell's equations modules in our PIC code OSIRIS 3.0, we intend to present our recent results of the analysis of MRI in collisionless plasma. Increasing the scale of our simulations, we will show the first ab-initio PIC simulations of a 2D turbulence induced consistently during the saturation regime of the MRI. We will demonstrate the existence of a minimum scale $\lambda_{kink}$ that determine the comparison of a drift-kink instability in the plasma. This instability will activate the turbulence during the saturation regime of the MRI. [Preview Abstract] |
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BP11.00038: Electron holes observed in the Moon Plasma Wake I H Hutchinson, D Malaspina, C Zhou Electrostatic instabilities are predicted in the magnetized wake of plasma flowing past a non-magnetic absorbing object such as a probe or the moon. Analysis of the data from the Artemis satellites, now orbiting the moon at distances ten moon radii and less, shows very clear evidence of fast-moving isolated solitary potential structures causing bipolar electric field excursions as they pass the satellite's probes. These structures have all the hallmarks of electron holes: BGK solitons typically a few Debye-lengths in size, self-sustaining by a deficit of phase-space density on trapped orbits. Electron holes are now observed to be widespread in space plasmas. They have been observed in PIC simulations of the moon wake to be the non-linear consequence of the predicted electron instabilities. Simulations document hole prevalence, speed, length, and depth; and theory can explain many of these features from kinetic analysis. The solar wind wake is certainly the cause of the overwhelming majority of the holes observed by Artemis, because we observe almost all holes to be in or very near to the wake. We compare theory and simulation of the hole generation, lifetime, and transport mechanisms with observations. [Preview Abstract] |
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BP11.00039: Plasma Electron Hole Oscillatory Velocity Instability Chuteng Zhou, Ian Hutchinson We report a new type of instability of electron holes (EHs) interacting with passing ions. The nonlinear interaction of EHs and ions is investigated using a new theory of hole kinematics. It is shown that the oscillation in the velocity of an EH parallel to the magnetic field direction becomes unstable when the hole velocity in the ion frame is slower than a few times the cold ion sound speed. This instability leads to the emission of ion-acoustic waves from the solitary hole and decay in its magnitude. The instability mechanism can drive significant perturbations in the ion density. The instability threshold, oscillation frequency and instability growth rate derived from our theory yield quantitative agreement with the observations from a novel high-fidelity hole-tracking Particle-In-Cell code. The instability can drive anomalous transport in space. Our result is important for studying slow electron holes that are strongly coupled to the ions. [Preview Abstract] |
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BP11.00040: Relay transport of relativistic flows in extreme magnetic fields of stars Weipeng Yao, Bin Qiao, Zheng Xu, Hua Zhang, Henxin Chang, Cangtao Zhou, Shaoping Zhu, Xiaogang Wang, Xiantu He We find that transport of relativistic flows in extreme magnetic fields can be achieved in a relay manner by considering the quantum electromagnetic (QED) cascade process, where photons play a key role as a medium. During the transport, the flow emits particle energy into photons via quantum synchrotron radiation and then gain particles back by magnetic pair creation, forming a ``particle-photon-particle" relay. Particle-in-cell simulations demonstrate that forward transport of the flow density is realized by a self-replenishment process with photon-pair cascades, while that of the flow energy is accomplished due to a new coupling path through radiation of photons. This novel transport mechanism is closely associated with jet generation and disk accretion around the neutron star of X-Ray Binaries, offering a potential explanation for the powerful jets observed there. [Preview Abstract] |
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BP11.00041: FRC |
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BP11.00042: Overview of C-2W Field-Reversed Configuration Experimental Program H. Gota, M.W. Binderbauer, T. Tajima, S. Putvinski, M. Tuszewski, S. Dettrick, S. Korepanov, J. Romero, A. Smirnov, Y. Song, M.C. Thompson, A. Van Drie, X. Yang, the TAE Team, A.A. Ivanov Tri Alpha Energy's research has been devoted to producing a high temperature, stable, long-lived field-reversed configuration (FRC) plasma state by neutral-beam injection (NBI) and edge biasing/control. C-2U experiments have demonstrated drastic improvements in particle and energy confinement properties of FRC's, and the plasma performance obtained via \textasciitilde 10 MW NBI has achieved plasma sustainment of up to 5 ms and plasma (diamagnetism) lifetimes of 10$+$ ms [1]. The emerging confinement scaling, whereby electron energy confinement time is proportional to a positive power of the electron temperature, is very attractive for higher energy plasma confinement; accordingly, verification of the observed $T_{e}$ scaling law will be a key future research objective. The new experimental device, C-2W (now also called ``Norman''), has the following key subsystem upgrades from C-2U: (i) higher injected power, optimum energies, and extended pulse duration of the NBI system; (ii) installation of inner divertors with upgraded edge-biasing systems; (iii) fast external equilibrium/mirror-coil current ramp-up capability; and (iv) installation of trim/saddle coils for active feedback control of the FRC plasma. This paper will review highlights of the C-2W program. \newline \newline [1] M.W. Binderbauer \textit{et al}., AIP Conf. Proc. \textbf{1721}, 030003 (2016). [Preview Abstract] |
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BP11.00043: Overview of the C-2W Field-Reversed Configuration Experiment Diagnostic Suite Matthew Thompson, Tania Schindler, Hiroshi Gota, Sergei Putvinski, Michel Tuszewski, Michl Binderbauer \underline {Tri Alpha Energy} (TAE) studies the evolution of advanced beam-driven field-reversed configuration (FRC) plasmas sustained by neutral-beam injection. Operations recently commenced on the C-2W device, which focuses on FRC heating and diamagnetic current build up [1]. Data on the FRC plasma is provided by an initial suite of diagnostics including magnetic sensors, interferometry, fast imaging cameras, Thomson scattering, and spectroscopy. Many more sophisticated diagnostics are also in preparation and commissioning: reflectometry, neutral particle analyzers, multi-chord FIR polarimetry, end loss analyzers, impurity and majority ion CHERS, FIDA, and 100 channel bolometers with proprietary compact local data acquisition. While many of these diagnostic systems were first implemented for the earlier C-2 and C-2U experiments [2], most had major upgrades for C-2W. TAE's diagnostics development program also works on novel systems including new ways to measure FRC internal magnetic fields. [1] M.W. Binderbauer et al., AIP Conf. Proc. 1721, 030003 (2016) [2] M.C. Thompson et al., Rev. Sci. Instrum. 87, 11D435 (2016) [Preview Abstract] |
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BP11.00044: C-2W Magnetic Measurement Suite T. Roche, M.C. Thompson, M. Griswold, K. Knapp, B. Koop, A. Ottaviano, M. Tobin Commissioning and early operations are underway on C-2W, Tri Alpha Energy's new FRC experiment. The increased complexity level of this machine requires an equally enhanced diagnostic capability. A fundamental component of any magnetically confined fusion experiment is a firm understanding of the magnetic field itself. C-2W is outfitted with over 700 magnetic field probes, \textasciitilde 550 internal and \textasciitilde 150 external. Innovative in-vacuum annular flux loop / B-dot combination probes will provide information about plasma shape, size, pressure, energy, total temperature, and trapped flux when coupled with establish theoretical interpretations. The massive Mirnov array, consisting of eight rings of eight 3D probes, will provide detailed information about plasma motion, stability, and MHD modal content with the aid of singular value decomposition (SVD) analysis. Internal Rogowski probes will detect the presence of axial currents flowing in the plasma jet in multiple axial locations. Initial data from this array of diagnostics will be presented along with some interpretation and discussion of the analysis techniques used. [Preview Abstract] |
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BP11.00045: Development of a Pulsed \textasciitilde 100MW Rotating Magnetic Field Ionization System for C-2W Erik Trask, Andrey Korepanov, Shannon Krause, Josh Leuenberger, Roger Smith, Travis Valentine, Will Waggoner The Rotating Magnetic Field (RMF) ionization system on the C-2W experiment at Tri Alpha Energy has been substantially upgraded from the previous system on the C-2U facility[1]. This system is used for ionizing gas prior to forming and accelerating Field-Reversed Configurations in the formation sections. Through the use of enhanced power units with increased stored energy, and an improved antenna design for better power coupling, a fully ionized plasma can now be produced in less than 100 us, in a background axial magnetic field in excess of 0.1 T, while at gas pressures in the \textasciitilde 1 mTorr range. The system design, characterization, and experimental ionization parameters will be discussed. [1]M.W. Binderbauer \textit{et al.}, AIP Conf. Proc. 1721, 030003 (2016) [Preview Abstract] |
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BP11.00046: High time resolution reconstruction of electron temperature profiles with a neural network in C-2U Gabriel Player, Richard Magee, Erik Trask, Sergey Korepanov, Ryan Clary, And the Tri Alpha Energy Team One of the most important parameters governing fast ion dynamics in a plasma is the electron temperature, as the fast ion-electron collision rate goes as $\nu_{ei}\sim T_{e}^{3/2}$. Unfortunately, the electron temperature is difficult to directly measure---methods relying on high-powered laser pulses or fragile probes lead to limited time resolution or measurements restricted to the edge. In order to rectify the lack of time resolution on the Thomson scattering data in the core, a type of learning algorithm, specifically a neural network, was implemented. This network uses 3 hidden layers to correlate information from nearly 250 signals, including magnetics, interferometers, and several arrays of bolometers, with Thomson scattering data over the entire C-2U database, totalling nearly 20,000 samples. The network uses the Levenberg-Marquardt algorithm with Bayesian regularization to learn from the large number of samples and inputs how to accurately reconstruct the entire electron temperature time history at a resolution of 500 kHz, a huge improvement over the 2 time points per shot provided by Thomson scattering. These results can be used in many different types of analysis and plasma characterization---in this work, we use the network to quantify electron heating. [Preview Abstract] |
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BP11.00047: Fast imaging and modeling of the C-2U outflow jet and pre-ionization plasmas Erik Granstedt, E Trask, R. J. Smith, S. Krause, D. Sheftman, and the TAE team The C-2U device\footnote{M.~Binderbauer, et~al. Physics of Plasmas \textbf{22}, 056110 (2015)} used neutral beam injection and end-biasing to maintain an advanced beam-driven Field-Reversed Configuration (FRC) plasma. A good electrical connection between the FRC and end-bias was critical for maintaining macroscopic stability. To model this electrical connection, characterization of the outflow jet plasma in this region is necessary. Limited access and the need for non-invasive instruments motivated optical diagnostics to be used for this purpose. High-speed cameras imaged visible light emission from neutral hydrogen and impurities. Tomographic reconstruction and neutral modeling was used to estimate the ionization rate and compare to the particle loss. The plasma macroscopic stability was also investigated. Imaging was also used to study the ``pre-ionization'' plasma in this region: the seed plasma which trapped the reversed magnetic flux during the initial FRC formation process. [Preview Abstract] |
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BP11.00048: Far infrared laser interferometry and polarimetry diagnostics for C-2W FRC experiment Bihe Deng, Mark Rouillard, Ping Feng, Michael Beall, Greg Settles, Greg Snitchler, Shawn Ziaei C-2W field-reversed configuration (FRC) experiments [1] are focused to resolve major physics issues facing the future of FRC devices. To achieve these goals, it is essential to measure the plasma equilibrium dynamics and monitor plasma fluctuations. One of the critical diagnostics under development is a 14-chord three-wave far infrared (FIR) laser interferometry and polarimetry system, which can provide simultaneous high temporal resolution measurements of density and Faraday rotation profiles with high accuracy. It is based on the previous successful experience of FIR polarimetry and interferometry measurements in C-2U FRC plasmas [2]. The physics considerations and the electro-opto-mechanical design and development of the system will be described, with discussions on challenges and solutions specific to diagnosing the high beta FRC plasmas. Initial experimental data will also be presented. [1] M.W. Binderbauer et al., AIP Conference Proceedings 1721, 030003 (2016). [2] B.H. Deng, et al., Rev. Sci. Instrum., 87, 11E125 (2016). [Preview Abstract] |
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BP11.00049: Measurement of magnetic null and field reversal in FRC plasmas using the Hanle effect Deepak Gupta, Kenneth Nordsieck, Richard Ignace, John Kinley, Marcel Nations In FRC plasmas, knowledge of the magnetic null location is required for understanding and comparison with theory and modeling. More fundamentally, one would first like to affirm the presence of field reversal. Conventional methods like internal magnetic probes, Zeeman effect, MSE, etc. have limitations, either due to their perturbative nature or the relatively low internal magnetic fields of FRCs. Here, use of the Hanle effect to measure the magnetic null and field reversal in an FRC is presented. The measurements utilize polarization of resonance radiation from the ions in the plasma using either external illumination or self-illumination. The mechanism of the Hanle effect, conditions of its use as a plasma diagnostic, and various schemes for measurements in an FRC will be presented, along with results from initial tests using a DC plasma discharge with varying magnetic field. The diagnostic design for the C-2W FRC plasma experiment will be discussed. [Preview Abstract] |
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BP11.00050: Characterization of the C-2W Plasma Guns Ami DuBois, Vladimir Sokolov, Sergey Korepanov, Dima Osin, Gabriel Player Previous use of coaxial arc discharge plasma guns on the C-2U device exhibited great success in plasma stabilization and improved confinement. On the C-2W experiment, arc discharge plasma guns will again be used to facilitate the electrical connection between the plasma core and the divertor electrodes in order to maintain the electrode edge biasing and induce E x B shear to control plasma rotation. Each plasma gun contains an internal solenoid used to shape the plasma stream. Characterization of electron density (n$_{\mathrm{e}})$, electron temperature (T$_{\mathrm{e}})$, floating potential (V$_{\mathrm{f}})$, and total plasma flux in an arc discharge lasting 6 ms without the internal solenoid are presented. A Langmuir probe located 27 cm axially outside of the plasma gun anode measures a bell-like radial n$_{\mathrm{e}}$ profile with peak n$_{\mathrm{e}}$ \textasciitilde 10$^{\mathrm{18}}$ m$^{\mathrm{-3}}$ and T$_{\mathrm{e}}$ \textasciitilde 2 - 10 eV. Observed spectral lines of impurity ions provide an estimate of T$_{\mathrm{e}}$, and Balmer series line ratios of the main ion component are used to evaluate n$_{\mathrm{e}}$ at both the probe location and near the plasma gun anode. A calorimeter measures the plasma flux to be constant and equivalent to 1 kA. [Preview Abstract] |
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BP11.00051: Multi-Wavelength Interferometry and Axial Polarimetry on C-2W R J Smith, S A Dettrick, M Onofri Tri Alpha Energy's C-2W device is operational and represents another major step in a progression of Field-Reversed Configuration (FRC) confinement devices that have prolonged the lifetime, increased stability and added significant neutral-beam injection power to heat and sustain an FRC plasma. Crucial to plasma sustainment and increased lifetime is an understanding of the jet plasma and X-point dynamics. To address these issues, a two-color multi-chord tangentially viewing interferometer has been designed and installed at the high field (mirror) position of the machine. CO$_{\mathrm{2}}$ and mmwave sources at 10.6 and 1000 um cover the density ranges of the translating FRC and the jet plasma. The small major radius at this location also provides the possibility for near on-axis axial interferometry/polarimetry using a standalone 150 \textmu m quantum cascade laser giving a measurement directly related to the amount of reversed flux in the FRC. Recent results from the jet interferometer and on-axis axial polarimetry results for simulated plasmas with ray tracing will be presented. [Preview Abstract] |
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BP11.00052: Near-infrared Bremsstrahlung radiation measurements in an advanced beam-driven FRC plasma Marcel Nations, Deepak Gupta, Nathan Bolte, Matthew C. Thompson, TAE Team In magnetically confined fusion plasmas, the effective ionic charge ($Z_{eff})$ is a measure of plasma impurity content. Knowledge of $Z_{eff}$ profiles is critical since impurities can account for substantial radiative power losses. One method to determine $Z_{eff}$ is to measure the Bremsstrahlung continuum over a small spectral range free from line radiation. In TAE's C-2 and C-2U machines, impurities in apparently line-free regions near 523 nm overwhelmed the expected Bremsstrahlung signals and resulted in overestimated values of $Z_{eff}$. The near-infrared region is less affected by impurities and better suited for accurate Bremsstrahlung continuum measurements. For C-2W, an upgraded diagnostic system will be deployed to measure Bremsstrahlung signals near 1000 nm. The near-infrared system uses a suite of silicon avalanche photodetectors paired with a D$_{\mathrm{\alpha }}$ system to remove contributions from neutrals and attain improved $Z_{eff}$ estimates. A design scheme for measurements in an FRC at multiple lines-of-sight is presented and discussed. [Preview Abstract] |
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BP11.00053: Development of Spatial Heterodyne Spectroscopy Measurements for the C-2W Plasma Expansion Divertor Daniel Sheftman, Tadafumi Matsumoto, Matthew Thompson Accurate operation and high performance of the open field line plasma surrounding the Field Reversed Configuration (FRC) is crucial to achieving the goals of successful temperature ramp up and confinement improvement on C-2W. Attributes such as the outflow velocity and temperature of charge exchange or impurity ions can be measured through spectroscopic methods. However, light throughput is severely limited due to the low plasma density inside the divertors where the plasma expands rapidly before terminating on biasing plates. A field widened spatial heterodyne spectrometer was developed in order to address the challenge of making accurate spectroscope measurements on the diffuse plasma. Design of a prototype of this spectrometer, including lab calibration and spectral line measurements performed on a compact toroid injector test stand, will be presented. [Preview Abstract] |
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BP11.00054: Studies on Plasmoid Merging using Compact Toroid Injectors Ian Allfrey, Tadafumi Matsumoto, Thomas Roche, Hiroshi Gota, Takahiro Edo, Tomohiko Asai, Daniel Sheftman, Dima Osin C-2 and C-2U experiments [1] have used magnetized coaxial plasma guns (MCPG) to inject compact toroids (CTs) for refueling the long-lived advanced beam-driven field-reversed configuration (FRC) plasma [2]. This refueling method will also be used for the C-2W experiment. To minimize momentum transfer from the CT to the FRC two CTs are injected radially, diametrically opposed and coincident in time. To improve understanding of the CT characteristics TAE has a dedicated test bed for the development of CT injectors (CTI), where plasmoid merging experiments are performed. The test bed has two CTIs on axis with both axial and transverse magnetic fields. The \textasciitilde 1 kG magnetic fields, intended to approximate the magnetic field strength and injection angle on C-2W, allow studies of cross-field transport and merging. Both CTIs are capable of injecting multiple CTs at up to 1 kHz. The resulting merged CT lives \textgreater 100 $\mu $s with a radius of \textasciitilde 25 cm. More detailed results of CT parameters will be presented. [1] M. Binderbauer et al., Physics of Plasmas, 22, 056110 (2015). [2] T. Matsumoto et al., Rev. Sci. Instrum. 87, 053512 (2016). [Preview Abstract] |
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BP11.00055: Performance Improvement of a Magnetized Coaxial Plasma Gun by adopting Iron-core Bias Coil and New Pre-Ionization System Takahiro Edo, T. Asai, F. Tanaka, S. Yamada, A. Hosozawa, H. Gota, T. Roche, I. Allfrey, T. matsumoto A magnetized coaxial plasma gun (MCPG) is a device used to generate a compact toroid (CT), which has a spheromak-like configuration. A typical MCPG consists of a set of axisymmetric cylindrical electrodes, bias coil, and gas-puff valves. In order to expand the CT operating range, the distributions of the bias magnetic field and neutral gas have been investigated. We have developed a new means of generating stuffing flux. By inserting an iron core into the bias coil, the magnetic field increases dramatically; even a small current of a few Amps produces a sufficient bias field. According to a simulation result, it was also suggested that the radial distribution of the bias field is easily controlled. The ejected CT and the target FRC are cooled by excess neutral gas that typical MCPGs require to initiate a breakdown [1,2]; therefore, we have adopted a miniature gun [3] as a new pre-ionization (PI) system. By introducing this PI system, the breakdown occurs at lower neutral gas density so that the amount of excess neutral gas can be reduced. [1] T. Matsumoto\textit{ et al}., Bull. Am. Phys. Soc. \textbf{61}, CP10.00083 (2016) [2] I. Allfrey\textit{ et al}., Bull. Am. Phys. Soc. \textbf{61}, CP10.00085 (2016) [3] T. Asai\textit{ et al}., Rev. Sci. Instrum. \textbf{81}, 10E119 (2010) [Preview Abstract] |
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BP11.00056: Bayesian Inference of FRC plasmas Jesus A. Romero, Sean Dettrick, Marco Onofri Bayesian analysis techniques are currently being used at TAE to infer FRC magnetic topology and the radial profile of the electron density. The Bayesian method provides all the solutions compatible with both the prior assumptions and the measurements in the form of a probability distribution termed the posterior, from which the most likely solution and its uncertainty can readily be obtained. Bayesian analysis of field reversed configurations reveals strong field reversal on axis as well as non-monotonic radial density profiles. The later feature is only observed in global transport simulations in cases where significant fast ion pressure and current drive are present. Hence the inferred non-monotonic density profiles are indicative of current drive in the experiment. [Preview Abstract] |
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BP11.00057: Separatrix $\mbox{E}\times \mbox{B}_{\mathrm{\thinspace \thinspace }}$Shear Flows and Turbulence Propagation in the C-2U FRC; Reflectometry Upgrades for C-2W Lothar Schmitz, Daniel Fulton, Calvin Lau, Ihor Holod, Zhihong Lin, Bihe Deng, Hiroshi Gota, Toshihiko Tajima, Michl Binderbauer Ion-scale modes were shown to be stable in the C-2/C-2U FRC core, in
agreement with gyrokinetic simulation results, with a characteristic
inverted toroidal wavenumber spectrum confirmed via Doppler Backscattering
(DBS). Multi-scale turbulence ($2 |
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BP11.00058: Fully-kinetic Ion Simulation of Global Electrostatic Turbulent Transport in C-2U Daniel Fulton, Calvin Lau, Jian Bao, Zhihong Lin, Toshiki Tajima Understanding the nature of particle and energy transport in field-reversed configuration (FRC) plasmas is a crucial step towards an FRC-based fusion reactor. The C-2U device at Tri Alpha Energy (TAE) achieved macroscopically stable plasmas and electron energy confinement time which scaled favorably with electron temperature$^{\mathrm{[1]}}$. This success led to experimental and theoretical investigation of turbulence in C-2U$^{\mathrm{[2],[3],[4],[5]}}$, including gyrokinetic ion simulations with the Gyrokinetic Toroidal Code (GTC). A primary objective of TAE's new C-2W device is to explore transport scaling in an extended parameter regime. In concert with the C-2W experimental campaign, numerical efforts have also been extended in A New Code (ANC) to use fully-kinetic (FK) ions and a Vlasov-Poisson field solver. Global FK ion simulations are presented. Future code development is also discussed. $^{\mathrm{[1]}}$ M. Binderbauer et al, Phys. Plasmas 22, 056110 (2015). $^{\mathrm{[2]}}$ L. Schmitz et al, Nat. Commun. 7, 13860 (2016). $^{\mathrm{[3]}}$ D. P. Fulton et al, Phys. Plasmas 23, 012509 (2016). $^{\mathrm{[4]}}$ D. P. Fulton et al, Phys. Plasmas 23, 056111 (2016). $^{\mathrm{[5]\thinspace }}$C. K. Lau et al, Phys. Plasmas, \textit{accepted for publication} (2017). [Preview Abstract] |
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BP11.00059: Cross-separatrix Coupling in Nonlinear Global Electrostatic Turbulent Transport in C-2U Calvin Lau, Daniel Fulton, Jian Bao, Zhihong Lin, Michl Binderbauer, Toshiki Tajima, Lothar Schmitz In recent years, the progress of the C-2/C-2U advanced beam-driven field-reversed configuration (FRC) experiments at Tri Alpha Energy, Inc. has pushed FRCs to transport limited regimes. Understanding particle and energy transport is a vital step towards an FRC reactor, and two particle-in-cell microturbulence codes, the Gyrokinetic Toroidal Code (GTC) and A New Code (ANC), are being developed and applied toward this goal. Previous local electrostatic GTC simulations find the core to be robustly stable with drift-wave instability only in the scrape-off layer (SOL) region. However, experimental measurements showed fluctuations in both regions; one possibility is that fluctuations in the core originate from the SOL, suggesting the need for non-local simulations with cross-separatrix coupling. Current global ANC simulations with gyrokinetic ions and adiabatic electrons find that non-local effects (1) modify linear growth-rates and frequencies of instabilities and (2) allow instability to move from the unstable SOL to the linearly stable core. Nonlinear spreading is also seen prior to mode saturation. We also report on the progress of the first turbulence simulations in the SOL. [Preview Abstract] |
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BP11.00060: Parallel Transport with Sheath and Collisional Effects in Global Electrostatic Turbulent Transport in FRCs Jian Bao, Calvin Lau, Animesh Kuley, Zhihong Lin, Daniel Fulton, Toshiki Tajima Collisional and turbulent transport in a field reversed configuration (FRC) is studied in global particle simulation by using GTC (gyrokinetic toroidal code). The global FRC geometry is incorporated in GTC by using a field-aligned mesh in cylindrical coordinates, which enables global simulation coupling core and scrape-off layer (SOL) across the separatrix. Furthermore, fully kinetic ions are implemented in GTC to treat magnetic-null point in FRC core. Both global simulation coupling core and SOL regions and independent SOL region simulation have been carried out to study turbulence [1-3]. In this work, the “logical sheath boundary condition” [4] is implemented to study parallel transport in the SOL. This method helps to relax time and spatial steps without resolving electron plasma frequency and Debye length, which enables turbulent transports simulation with sheath effects. We will study collisional and turbulent SOL parallel transport with mirror geometry and sheath boundary condition in C2-W divertor. [1] D. Fulton et al, Phys. Plasmas 23, 012509 (2016); Phys. Plasmas 23, 056111 (2016). [2] L. Schmitz et al, Nat. Communications 7, 13860 (2016). [3] C. Lau et al, Phys. Plasmas 24, in press (2017). [4] S. Parker et al, J. Comput. Phys. 104, 41-49 (1993). [Preview Abstract] |
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BP11.00061: Whole Device Modeling of Compact Tori: Stability and Transport Modeling of C-2W Sean Dettrick, Daniel Fulton, Calvin Lau, Zhihong Lin, Francesco Ceccherini, Laura Galeotti, Sangeeta Gupta, Marco Onofri, Toshiki Tajima Recent experimental evidence from the C-2U FRC experiment shows that the confinement of energy improves with inverse collisionality [1], similar to other high beta toroidal devices, NSTX [2,3] and MAST [4]. This motivated the construction of a new FRC experiment, C-2W, to study the energy confinement scaling at higher electron temperature. Tri Alpha Energy is working towards catalysing a community-wide collaboration to develop a Whole Device Model (WDM) of Compact Tori. One application of the WDM is the study of stability and transport properties of C-2W using two particle-in-cell codes, ANC and FPIC. These codes can be used to find new stable operating points, and to make predictions of the turbulent transport at those points. They will be used in collaboration with the C-2W experimental program to validate the codes against C-2W, mitigate experimental risk inherent in the exploration of new parameter regimes, accelerate the optimization of experimental operating scenarios, and to find operating points for future FRC reactor designs. [1] M. Binderbauer, et al., Phys. Plasmas, 22 (2015) 56110; [2] S. Kaye, et al. Nucl. Fusion, 47 (2007) 499; [3] S. Kaye, et al. Nucl. Fusion, 53 (2013) 63005; [4] M. Valovič, et al. Nucl. Fusion, 51 (2011) 73045 [Preview Abstract] |
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BP11.00062: Vlasov Fokker Planck Study of Electron Dynamics in the Scrape Off Layer with Expander Divertor S. Gupta, P. Yushmanov, The TAE TEAM, D. C. Barnes Control of electron heat losses in the open field region surrounding a Field Reversed Configuration (FRC) is important for sustaining higher temperatures in the FRC core, for favorable beam energy deposition, and for reducing loads on divertor plates. At TAE, a magnetic expander will be used to attain these objectives in the new C-2W machine and to comprehensively study expander divertor physics. The electron dynamics and electrostatic potential formation in the expanding magnetic field is analyzed using a 3-D (2 velocity and 1 spatial) Vlasov Fokker Planck code (Ksol). Numerical results showing the effect of collisionality, current, Z$_{\mathrm{eff}}$, incoming distribution etc., on the formation of electrostatic potentials will be presented. [Preview Abstract] |
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BP11.00063: Characterization of magnetohydrodynamic transport in a Field Reversed Configuration Marco Onofri, Peter Yushmanov, Sean Dettrick, Daniel Barnes, Kevin Hubbard, Toshi Tajima Transport in a Field Reversed Configuration (FRC) is studied by using the two-dimensional code Q2D, which couples a magnetohydrodynamic code with a Monte Carlo code for the beam component. The simulation by Q2D of the parallel transport in the simple open $\theta $-pinch fields and its associated outflow shows an excellent agreement with one of the existing theories, providing a benchmark for Q2D and simultaneously deepening the theoretical understanding of this fundamental process. We find a sharp distinction between the evolved radial density profiles of the FRC and mirror plasmas as a result of the transport processes, showing that the closed flux surfaces of an FRC enhance the confinement over that of a mirror. We characterize the scrape-off layer (SOL) transport by including the mirror trapping effects and we find a relation between the confinement time in the SOL and the ion collisional time. The Q2D code is also used to study the formation of the electrostatic potential in the divertor. [Preview Abstract] |
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BP11.00064: Synchrotron Radiation From Plasmas with Sub-Relativistic Temperatures Ales Necas, Sergei Putvinski, Dmitri Ryutov, Peter Yushmanov A simple expression for power radiated by synchrotron radiation from plasmas with electron temperatures between 50 -- 200 keV is developed. We shall start by re-deriving [1] a general expression for power radiated in vacuum from an individual cyclotron harmonic. Adding up power radiated from individual harmonics shows an asymptotic approach to the power radiated from all harmonics. In a case of Te$=$50 keV, summing the first 10 harmonics well represents radiation from all harmonics. However, for Te$=$150 keV, we require to sum over 60 harmonics to adequately represent the total radiation. This is computationally demanding. What follows is a derivation of a simple expression for high harmonic power radiation in vacuum. It is of interested that this expression proofs to be reasonable even for low harmonic numbers. Next we shall present the derivation of the relativistic frequency spectra. A discussion of cut-off for the electromagnetic O-wave and X-wave follows as well as re-emission of synchrotron radiation. Wave propagation close to perpendicular to B field is assumed. [1] Landau, L.D. and Lifshitz, E.M., \textit{Classical Theory of Fields}, New York: Pergamon Press, 1971. Eq. 74.9 [Preview Abstract] |
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BP11.00065: Stabilization of Beam-Driven Modes by Ionization-Induced Velocity Spread Bradley Nicks, Ales Necas, Toshiki Tajima Using the implicit PIC code LSP, the stabilization of beam-driven modes by ionization-induced velocity-space broadening in 2D is analyzed. A neutral beam of hydrogen with variable temperature and energy is injected into a high-$\beta $ background plasma of deuterium and electrons, and a model of ionization creates fast ions from the neutrals. The plasma is then examined for instabilities. Micro-instabilities manifest as periodic nodes in velocity space (chiefly with long wavelength, such as Bernstein or AIC modes), while macro-instabilities additionally create periodic structures in real space, such as a cyclotron theta mode on the beam ions. For this study, the background plasma is first taken to have uniform density and $B_{z}$, and second, an FRC profile. In previous 1D studies without ionization-induced effects, many unstable beam-driven modes were found. With the injection of a neutral beam into a 2D geometry however, many of these modes are stabilized by the broadening of the beam velocity-space distribution. The broadening is strongest for $v_{\mathrm{\bot }}$, spanning several multiples of the original neutral beam drift speed. Similarly, real-space spreading stabilizes macro-instabilities. Criteria for stability based on the degree of velocity-space and real-space spreading are found and are compared with the 1D case. [1] \textit{Tri Alpha Energy, Inc., Rancho Santa Margarita, CA 92688, USA. }[2]\textit{ University of California Irvine, Irvine, CA 92697, USA. } [Preview Abstract] |
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BP11.00066: Numerical Study of HHFW Heating in FRC Plasmas Francesco Ceccherini, Laura Galeotti, Marco Brambilla, Sean Dettrick, Xiaokang Yang The TriAlpha Energy (TAE) code RF-Pisa is a Finite Larmor Radius (FLR) full wave code developed over the years to study RF heating in the Field Reversed Configuration (FRC) in both the ion and electron cyclotron regimes. The FLR approximation is perfectly adequate to address RF propagation and absorption at the fundamental and second harmonic frequencies (as in the minority heating scheme), but it is not able to describe higher order processes such as high-harmonic fast waves (HHFW). The latter ones have frequencies lying between the ion cyclotron and lower hybrid resonances and they may represent a viable path to develop an efficient method to deposit energy inside the FRC separatrix, as suggested by recent results obtained at NSTX. A significant upgrade of RF-Pisa to include HHFW has been undertaken. In particular, the so-called “quasi local approximation” [1] originally proposed for toroidal geometries has been re-derived for the cylindrical geometry and a new HHFW version of RF-Pisa concurrent to the FLR version has been developed. Here we present the first results of the application of the new code to FRC equilibria and we discuss the features of the dispersion relations and the absorption processes which characterize this novel regime. [1] Brambilla, PPCF, 44, 2423 (2002) [Preview Abstract] |
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BP11.00067: Energy spectrum and kinetics of the fusing particles D.D. Ryutov, S.V. Putvinski, P.N. Yushmanov, ,and the TAE Team The fusing particles (e.g., D and T, or p and $^{\mathrm{11}}$B) contribution to the reaction rate can be found by the integration of the fusion reactivity over the particle distribution functions. The~distribution function (e.g., Maxwellian) is depleted in the energy range determined by the highest reactivity and has to be replenished by particle collisions. The kinetics of the replenishment process may affect the rate of fusion energy release. We present a simple analysis of the corresponding kinetic problems for the conditions typical for the standard and advanced-fuel fusion reactions and assess the possible effect on the reaction yield. [Preview Abstract] |
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BP11.00068: PMI |
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BP11.00069: Understanding the Effect of Gas Dynamics in Plasma Gun Performance for Simulating Fusion Wall Response to Disruption Events Will Riedel, Thomas Underwood, Fabio Righetti, Mark Cappelli In this work, the suitability of a pulsed coaxial plasma accelerator to simulate the interaction of edge-localized modes with plasma first wall materials is investigated. Experimental measurements derived from a suite of diagnostics are presented that focus on both the properties of the plasma flow and the manner in which such jets couple with material interfaces. Specific emphasis is placed on quantifying the variation in these properties using tungsten tokens exposed to the plasma plume as the gun volume is progressively filled with more neutral gas. These results are mapped to the operational dynamics of the gun via a time-resolved Schlieren cinematic visualization of the density gradient within the flow. Resulting videos indicate the existence of two distinct modes with vastly different characteristic timescales, spatial evolution, and plasma properties. Time resolved quantification of the associated plasma heat flux for both modes, including a range spanning 150 MW m$^{-2}$ - 10 GW m$^{-2}$, is presented using both a fast thermocouple gauge and an IR camera. Both diagnostics in conjunction with a heat transfer model provide an accurate description of the energy transfer dynamics and operational characteristics of plasma guns. [Preview Abstract] |
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BP11.00070: Erosion and Surface Morphology of Silicon Carbide Under Variable DIII-D Divertor Heat Fluxes Stefan Bringuier, Tyler Abrams, Hesham Khalifa, Dan Thomas, Leo Holland, Dmitry Rudakov, Alexis Briesemeister A SiC coating of \textasciitilde 250 $\mu $m, deposited onto a graphite DiMES cap via chemical vapor deposition, was exposed to \textasciitilde 80 s of H-mode plasma bombardment in the DIII-D outer divertor with steady-state heat fluxes up to 3 MW m$^{\mathrm{-2}}$ and transient loads due to ELMs typically peaking at \textasciitilde 10 MW m$^{\mathrm{-2}}$. In-situ monitoring of Si I and Si II atomic spectral lines revealed the presence of significant neutral Si and Si$^{\mathrm{+}}$ impurity influx, which are used to determine quantitative erosion rates via the S/XB method. No visual macroscopic flaking or delamination of the SiC coating was observed, supporting the notion that SiC is thermal-mechanically robust and compatible with graphite substrates at elevated temperatures. Post-mortem profilometric analysis also indicates no pronounced change in surface roughness after plasma exposure. Finally, we investigate aspects of preferential sputtering and changes to surface composition exposure using scanning electron microscopy and Auger electron spectroscopy. [Preview Abstract] |
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BP11.00071: Development and Testing of Dispersion-Strengthened Tungsten Alloys via Spark Plasma Sinterin Eric Lang, Nathan Madden, Charles Smith, Jessica Krogstad, Jean Paul Allain Tungsten (W) is a common plasma-facing component (PFC) material in the divertor region of tokamak fusion devices due to its high melting point and high sputter threshold [1]. However, W is intrinsically brittle and is further embrittled under neutron irradiation, and the low recrystallization temperature pose complications in fusion environments [1,2]. More ductile W alloys, such as dispersion-strengthened tungsten are being developed. In this work, W samples are processed via spark plasma sintering (SPS) with TiC, ZrC, and TaC dispersoids alloyed from 0.5 to 10 weight {\%}. SPS is a powder compaction technique that provides high pressure and heating rates via electrical current, allowing for a lower final temperature and hold time for compaction [3]. Initial testing of material properties, smicrostructure, and composition of specimens will be presented. Deuterium and helium irradiations have been performed in IGNIS, a multi-functional, \textit{in-situ }irradiation and characterization facility at the University of Illinois. High-flux, low-energy exposures at the Magnum-PSI facility at DIFFER exposed samples to a D fluence of 1x10$^{\mathrm{26\thinspace }}$cm$^{\mathrm{-2\thinspace }}$and He fluence of 1x10$^{\mathrm{25}}$-1x10$^{\mathrm{26}}$ cm$^{\mathrm{-2}}$ at temperatures of 300-1000 C. \textit{In-situ} chemistry changes via XPS and \textit{ex-situ} morphology changes via SEM will be studied. [1] D. Naujoks, et al. \textit{Nucl. ~Fusion}. Vol 36,~No. 6 (1996) [2] S.J. Zinkle, et al. \textit{Annu. Rev. Mater. Res.} 2014. 44:241--67. [3] J.R. Groza, et al. \textit{Mat. Sci. and Eng. }A287 (2000) 171-177. Work supported by US DOE Contract DE-SC0014267 [Preview Abstract] |
(Author Not Attending)
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BP11.00072: Investigation of the helium effects on deuterium retention in thin film lithium coatings on tungsten substrates A.L. Neff, J.P. Allain, T.W. Morgan In a burning fusion plasma, the materials on the walls of the plasma vessel will have a significant effect on the performance of the plasma. Any amount of high Z wall material that is eroded will contaminate and cool the plasma and may lead to a disruption. Additionally, if the material retains or reflects fuel it can affect the stability of the plasma. A high recycling wall that retains minimal fuel will allow better control of the fuel inventory, especially tritium, in the walls [1]. In contrast, a low recycling wall leads to improved plasma performance by preventing instabilities in the plasma [2]. We have observed that when 5{\%} He is added to D ions during low flux (10$^{\mathrm{17}}$ m$^{\mathrm{-2}}$s$^{\mathrm{-1}})$ dual ion beam irradiation the amount of D retained in the Li film diminishes [3]. This conclusion is based on the reduction of a XPS peak (at 533 eV) associated with D retention in Li films [4]. To further investigate this phenomenon, we have continued the dual beam studies in IGNIS (Ion-Gas-Neutral Interactions with Surfaces) by varying the energy and concentration of He to D. Additionally, we exposed lithiated W to sequential D and He plasmas (10$^{\mathrm{24}}$ m$^{\mathrm{-2}}$s$^{\mathrm{-1}}$ flux) in Magnum PSI at DIFFER. With XPS, we analyzed the chemistry of the Li films and determined changes in retention. These results will be presented. [1] G. De Temmerman, et al., Nucl. Mater. Energy (In Press). [2] H.W. Kugel, et al., J. Nucl. Mater. 390--391 (2009) 1000--1004. [3] A.L. Neff, M.S. Thesis, Purdue Univ., 2013. [4] C.N. Taylor, et al., J. Appl. Phys. 109 (2011) 053306-053306-6. [Preview Abstract] |
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BP11.00073: Hydrogen retention in Li and Li-C-O films Luxherta Buzi, Andrew O. Nelson, Yuxin Yang, Robert Kaita, Bruce E. Koel The efficiency of Li in binding H isotopes has led to reduced recycling in magnetic fusion devices and improved plasma performance. Since elemental Li surfaces are challenging to maintain in fusion devices due to the presence of impurities, parameterizing and understanding the mechanisms for H retention in various Li compounds (Li-C-O), in addition to pure Li, is crucial for Li plasma-facing material applications. To determine H retention in Li and Li-C-O films, measurements were done under ultrahigh vacuum conditions using temperature programmed desorption (TPD). Thin Li films (20 monolayers) were deposited on a nickel single crystal substrate and irradiated with 500 eV H$_{\mathrm{2}}^{\mathrm{+}}$ ions at surface temperatures from 90K to 520K. Initial measurements on Li and Li-O films showed that the retention was comparable and dropped exponentially with surface temperature, from 95{\%} at 90 K to 35{\%} at 520 K. Auger electron spectroscopy and TPD showed that H was retained as lithium hydride (LiH) in pure Li and as lithium hydroxide (LiOH) in Li$_{\mathrm{2}}$O, which decomposed to H$_{\mathrm{2}}$O and Li$_{\mathrm{2}}$O at temperatures higher than 470K. H retention in Li-C and Li-C-O films will be determined over a similar temperature range, and the sputtering rate of these layers with H ions will also be reported. [Preview Abstract] |
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BP11.00074: Deuterium sputtering of Li and Li-O films Andrew Nelson, Luxherta Buzi, Robert Kaita, Bruce Koel Lithium wall coatings have been shown to enhance the operational plasma performance of many fusion devices, including NSTX and other tokamaks, by reducing the global wall recycling coefficient. However, pure lithium surfaces are extremely difficult to maintain in experimental fusion devices due to both inevitable oxidation and codeposition from sputtering of hot plasma facing components. Sputtering of thin lithium and lithium oxide films on a molybdenum target by energetic deuterium ion bombardment was studied in laboratory experiments conducted in a surface science apparatus. A Colutron ion source was used to produce a monoenergetic, mass-selected ion beam. Measurements were made under ultrahigh vacuum conditions as a function of surface temperature (90-520 K) using x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and temperature programmed desorption (TPD). Results are compared with computer simulations conducted on a temperature-dependent data-calibrated (TRIM) model. [Preview Abstract] |
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BP11.00075: Flux threshold determination for tungsten nano-fuzz formation using an 80 eV He-ion beam Fred W. Meyer, Mark E. Bannister, Chad M. Parish At the ORNL Multicharged Ion Research Facility (MIRF), we have extended our investigation of flux thresholds for He-ion induced nano-fuzz formation on hot tungsten surfaces down to plasma-edge-relevant energies of 80 eV. We measured the size of the incident ion beam by accurate flux-profile measurements, and the size of the region where tungsten nano-fuzz was formed by post-exposure SEM surface analysis and real-time monitoring of the hot W surface-emissivity change throughout the beam exposure. If tungsten nano-fuzz formation had a fluence threshold, the size of the observed nano-fuzz region would be expected to increase with exposure time, eventually filling the entire ion beam spot. Instead, we found that the region of nano-fuzz formation (1) was always smaller than the beam spot itself and (2) did not increase in size with time, i.e. with accumulated He ion fluence. By comparison of the flux profile and the spatial extent of the fuzz region we determined a flux threshold of 9.5$+$-3x10$^{\mathrm{19}}$/m$^{\mathrm{2}}$s at 80 eV He ion impact energy. We show that the observed flux-threshold energy dependence for nano-fuzz formation, which we have now mapped out from 80 eV to 8.5 keV, is well reproduced by the combined energy dependences of He-ion reflection, He-ion range and target-damage creation, determined using SRIM. [Preview Abstract] |
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BP11.00076: Production of high-density highly-ionized helicon plasmas in the ProtoMPEX J.F. Caneses, N. Kafle, M. Showers, R.H. Goulding, T.M. Biewer, J.B.O. Caughman, T. Bigelow, J. Rapp High-density (2-6e19 m-3) Deuterium helicon plasmas in the ProtoMPEX have been produced that successfully use differential pumping to produce neutral gas pressures suitable for testing the RF electron and ion heating concepts. To minimize collisional losses when heating electrons and ions, plasmas with very low neutral gas content (\textless \textless 0.1 Pa) in the heating sections are required. This requirement is typically not compatible with the neutral gas pressures (1-2 Pa) commonly used in high-density light-ion helicon sources. By using skimmers, a suitable gas injection scheme and long duration discharges (\textgreater 0.3 s), high-density plasmas with very low neutral gas pressures (\textless \textless 0.1 Pa) in the RF heating sections have been produced. Measurements indicate the presence of a highly-ionized plasma column and that discharges lasting at least 0.3 s are required to significantly reduce the neutral gas pressure in the RF heating sections to levels suitable for investigating electron/ion RF heating concepts in this linear configuration. [Preview Abstract] |
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BP11.00077: Measurements of ion energies during plasma heating of the Proto-MPEX High Intensity Plasma Source J.B.O. Caughman, R.H. Goulding, T.M. Biewer, T.S. Bigelow, J. Caneses, S.J. Diem, D.L. Green, R.C. Isler, J. Rapp, P. Piotrowicz, C.J. Beers, N. Kafle, M.A. Showers The Prototype Materials Plasma Exposure eXperiment (Proto-MPEX) is a linear high-intensity RF plasma source that combines a high-density helicon plasma generator with ion and electron heating sections. It is being used to study the physics of heating over-dense plasmas in a linear configuration with the goal of delivering a plasma heat flux of \textasciitilde 10 MW/m$^{\mathrm{2}}$ at a target. The helicon plasma is produced by coupling 13.56 MHz RF power at levels \textgreater 100 kW. Additional heating is provided by ion cyclotron heating (ICH) (\textasciitilde 25 kW) and electron Bernstein wave (EBW) heating (\textasciitilde 25 kW) at 28 GHz. Measurements of the ion energy distribution with a retarding field energy analyzer (RFEA) show an increase in ion energies in the edge of the plasma when ICH is applied, which is consistent with COMSOL modeling of the power deposition from the antenna. Views of the target plate with an infrared camera show an increase in the surface temperature at large radii during ICH, and these areas map back to magnetic field lines near the antenna. The change in the power deposition at the target during ICH is compared with Thomson Scattering and RFEA measurements near the target. [Preview Abstract] |
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BP11.00078: Modeling and Theory of RF Antenna Systems on Proto-MPEX P.A. Piotrowicz, J.F. Caneses, R.H. Goulding, D. Green, J.B.O. Caughman, D.N. Ruzic The RF wave coupling of the helicon and ICH antennas installed on the Prototype Material Plasma Exposure eXperiment (MPEX) has been explored theoretically and via a full wave model implemented in COMSOL Multiphysics. The high-density mode in Proto-MPEX has been shown to occur when exciting radial eigenmodes of the plasma column which coincides with entering a Trivelpiece Gould (TG) anti-resonant regime, therefore suppressing edge heating in favor of core power deposition. The fast wave launched by the helicon antenna has a large wavelength and travels at a steep group velocity angle with the background magnetic field; for this reason the fast wave launched by the helicon antenna efficiently couples power to the core plasma. However, the ICH heating scheme relies on a small wavelength slow wave to couple power to the core of the plasma column. Coupling slow wave power to the core of the plasma column is sensitive to the location of the Alfven resonance. The wave-vector and group velocity vector of the slow wave in this parameter regime undergoes a drastic change in behavior when approaching the Alfven resonance. Full wave simulation results and dispersion analysis will be presented with suggestions to guide experimental progress. [Preview Abstract] |
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BP11.00079: High power plasma heating experiments on the Proto-MPEX facility T.S. Bigelow, C.J. Beers, T.M. Biewer, J.F. Caneses, J.B.O. Caughman, S.J. Diem, R.H. Goulding, D.L. Green, N. Kafle, J. Rapp, M.A. Showers Work is underway to maximize the power delivered to the plasma that is available from heating sources installed on the Prototype Materials Plasma Exposure eXperiment (Proto-MPEX) at ORNL. Proto-MPEX is a linear device that has a \textgreater 100 kW, 13.56 MHz helicon plasma generator available and is intended for material sample exposure to plasmas. Additional plasma heating systems include a 10 kW 18 GHz electron cyclotron heating (ECH) system, a 25 kW \textasciitilde 8 MHz ion cyclotron heating ICH system, and a 200 kW 28 GHz electron Bernstein wave (EBW) and ECH system. Most of the heating systems have relatively good power transmission efficiency, however, the 28 GHz EBW system has a lower efficiency owing to stringent requirements on the microwave launch characteristics for EBW coupling combined with the lower output mode purity of the early-model gyrotron in use and its compact mode converter system. A goal for the Proto-MPEX is to have a combined heating power of 200 kW injected into the plasma. Infrared emission diagnostics of the target plate combined with Thomson Scattering, Langmuir probe, and energy analyzer measurements near the target are utilized to characterize the plasmas and coupling efficiency of the heating systems. [Preview Abstract] |
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BP11.00080: Observations of temperature rise during electron cyclotron heating application in Proto-MPEX T.M. Biewer, T. Bigelow, J.F. Caneses, S.J. Diem, J. Rapp, M. Reinke, N. Kafle, H.B. Ray, M. Showers The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) at ORNL utilizes a variety of power systems to generate and deliver a high heat flux plasma (~1 MW/m2 for these discharges) onto the surface of material targets. In the experiments described here, up to 120 kW of 13.56 MHz “helicon” waves are combined with ~20 kW of 28 GHz microwaves to produce Deuterium plasma discharges. The 28 GHz waves are launched in a region of the device where the magnetic field is axially varying near ~0.8 T, resulting in the presence of a 2nd harmonic electron cyclotron heating (ECH) resonance layer that transects the plasma column. The electron density and temperature profiles are measured using a Thomson scattering (TS) diagnostic, and indicate that the electron density is radially peaked. In the core of the plasma column the electron density is higher than the cut-off density (0.9x1019 m-3) for ECH waves to propagate and O-X-B mode conversion into electron Bernstien waves (EBW) is expected. TS measurements indicate electron temperature increases during 28 GHz wave application, rising (from ~5 eV to ~20 eV) as the neutral Deuterium pressure is reduced below 1 mTorr. [Preview Abstract] |
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BP11.00081: Power Balance Analysis of the Prototype-Material Plasma Exposure eXperiment M.A. Showers, T.M. Biewer, J.F. Caneses, J.B.O Caughman, A. Lumsdaine, L. Owen, J. Rapp, D. Youchison, C.J. Beers, D.C. Donovan, N. Kafle, H.B. Ray The Prototype-Material Plasma Exposure eXperiment (Proto-MPEX) is a test bed for the plasma source concept for the planned Material Plasma Exposure eXperiment (MPEX), a steady-state linear device studying plasma material interactions for fusion reactors. A power balance of Proto-MPEX attempts to identify machine operating parameters that will improve Proto-MPEX's performance, potentially impacting the MPEX design concept. A power balance has been performed utilizing an extensive diagnostic suite to identify mechanisms and locations of power loss from the main plasma. The diagnostic package includes infrared cameras, double Langmuir probes, fluoroptic probes, Mach probes, a Thomson scattering diagnostic, a McPherson spectrometer and in-vessel thermocouples. Radiation losses are estimated with absolute calibrated spectroscopic signals. [Preview Abstract] |
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BP11.00082: Experimental results from plasma transport on Prototype-Material Plasma Exposure eXperiment and comparison with B2-Eirene modeling N. Kafle, J.F. Caneses, T.M. Biewer, L. Owen, M. Showers, D. Donovan, J.B. Caughman, R.H. Goulding, Juergen Rapp Proto-MPEX at ORNL is a linear plasma device that combines a helicon plasma source with additional microwave and RF heating to deliver high plasma heat and particle fluxes to a target. Double Langmuir probes and Thomson scattering are being used to measure local Te and ne at various radial and axial locations. A recently constructed Mach- double probe provides the added capability of simultaneously measuring Te, ne, and Mach number. With this diagnostic, it is possible to infer the plasma flow, particle flux, and convective heat flux at different locations along the plasma column in Proto-MPEX. Preliminary results show Mach numbers of 0.6 and 0.8 in either direction away from the helicon source, and no flow near the source for the case where the peak magnetic field was 1.0 T. In addition, the Thomson Scattering system has been upgraded to measure ne and Te profiles at two axial locations, upstream at the electron heating location and downstream close to the target. Measurements of particle flow and flux profiles, heat flux, and profiles of ne and Te will be discussed. The extensive coverage provided by these diagnostics permits data-constrained B2-Eirene modeling of the entire plasma column, and comparison with results of modeling of high density mode plasmas will be presented. [Preview Abstract] |
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BP11.00083: Development and Implementation of a New HELIOS Diagnostic using a Fast Piezoelectric Valve on the Prototype Material Plasma Exposure eXperiment Holly Ray, Theodore Biewer, Juan Caneses, Jonathan Green, Elizabeth Lindquist, Levon McQuown, Oliver Schmitz A new helium line-ratio spectral monitoring (HELIOS) diagnostic, using a piezoelectric valve with high duty cycles (on/off times~ ms), allowing for good background correction, and measured particle flowrates on the order of \textasciitilde 1020 particles/second is being implemented on Oak Ridge National Laboratory's (ORNL) Prototype Material Plasma Exposure eXperiment (Proto-MPEX).~ Built in collaboration with the University of Wisconsin -- Madison, the HELIOS diagnostic communicates with a Labview program for controlled bursts of helium into the vessel.~ The open magnetic geometry of Proto-MPEX is ideal for testing and characterizing a HELIOS diagnostic.~ The circular cross-section with four ports allows for cross comparison between different diagnostics:~ 1) Helium injection with the piezoelectric puff valve, 2) HELIOS line-of-sight high-gain observation, 3) scan-able Double Langmuir probe, and 4) HELIOS 2D imaging observation. Electron density and temperature measurements from the various techniques will be compared. [Preview Abstract] |
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BP11.00084: Development of a Dual-Laser Digital Holography Diagnostic for Surface Characterization at ORNL J.C. Sawyer, T.M. Biewer, C.E. Thomas, Z. Zhang The Fusion and Materials for Nuclear Systems Division (FMNSD) at Oak Ridge National Laboratory (ORNL), in collaboration with The University of Tennessee, Knoxville and Third Dimension Technologies (TDT), presents continuing progress towards the development of a dual-laser digital holography (DH) technique for 3D imaging of plasma facing component (PFC) surfaces in real time. This update includes results from an ``on the bench'' single-laser DH demonstration. The dual-laser approach utilizes two CO$_{\mathrm{2}}$ lasers tuned to neighboring molecular CO$_{\mathrm{2}}$ lines to extend the 2$\pi $ ambiguity of holographic interferograms to $\sim $5 mm from the $\sim $10 $\mu $m wavelength. Reconstruction of the interferogram allows for measurement of changes in surface topology at rates of $\sim $2 mm/s. This status of a dual-laser DH system ``on the bench,'' demonstration and implementation on the Proto-MPEX device will be presented. [Preview Abstract] |
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BP11.00085: Numerical Assessment of Plasma Parameters and Surface Flux Scaling in the HIDRA Stellarator Steven Marcinko, Davide Curreli Pre-online scaling of expected HIDRA operating conditions has been analyzed using EMC3-EIRENE, to which a self-consistent local Bohm-like diffusivity has been added. An inboard and outboard midplane limiter were tested with RF input to core-edge power deposition efficiencies of 10-50\% for a 26 kW 2.45 GHz combined RF input discharge. Scaling laws for peak electron temperature, Bohm-like diffusivity, and heat and particle fluxes have been calculated for both low- and high-field discharges; peak electron temperatures, particle diffusivity, and heat fluxes at the outboard limiter were seen to follow approximately a power-law of type $f(P_{RF})\propto a P_{RF}^b$, with typical exponents in the range $b \sim 0.55 - 0.60$. Higher magnetic fields have the tendency to linearize the heat flux dependence upon the RF power, with exponents in the range of $b \sim 0.75$. Particle fluxes on the outboard limiter are seen to saturate first, and then slightly decline for RF powers in excess of 120 kW in the low-field case and 180 kW in the high-field case. [Preview Abstract] |
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BP11.00086: Investigation Of A Tin-Lithium Alloy As A Liquid Plasma-Facing Material Heather Sandefur, David Ruzic, Robert Kolasinski, Dean Buchenauer Sn-Li is a low melting-point alloy that has been identified as a material with favorable performance in plasma material interaction studies. While lithium is a low Z material with a demonstrated ability to absorb impinging ions, pure lithium is plagued by high evaporation rates in the liquid phase. The Sn-Li alloy is a more stable alternative that provides a lower rate of evaporative flux due to the high vapor pressure of tin. In the liquid phase, the bulk segregation of lithium to the surface of the material has also been observed. While the alloy is of considerable interest, little data has been collected on its surface chemistry in a plasma environment. In order to expand the existing body of knowledge in this area, samples of an 80 percent Sn---20 percent Li alloy were prepared and analyzed in order to assess the surface composition and degree of lithium segregation in the liquid phase. The Angle-Resolved Ion Energy Spectrometer (ARIES) at Sandia National Laboratories was used to probe the surfaces of the alloy using the low energy ion scattering method. The lithium coverage at the surface was measured, and the material's affinity for hydrogen chemisorption was investigated. [Preview Abstract] |
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BP11.00087: ENERGETIC PARTICLES |
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BP11.00088: Modelling ion cyclotron emission from KSTAR tokamak and LHD helical device plasmas Richard Dendy, Ben Chapman, Bernard Reman, Sandra Chapman, Tsuyoshi Akiyama, Gunsu Yun New high quality measurements of ion cyclotron emission (ICE) from KSTAR and LHD greatly extend the scope and diversity of plasma conditions under which ICE is observed. Variables include the origin (fusion reactions or neutral beam injection) and energy (sub- or super-Alfv\'{e}nic) of the minority energetic ions that drive ICE; the composition of the bulk plasma (hydrogen or deuterium) which supports the modes excited; plasma density in the emitting region, and the timescale on which it changes; and toroidal magnetic field geometry (tokamak or helical device). Future exploitation of ICE as a diagnostic for energetic ion populations in JET D-T plasmas and in ITER rests on quantitative understanding of the physics of the emission. This is tested and extended by current KSTAR and LHD measurements of ICE. We report progress on direct numerical simulation using full orbit ion kinetic codes that solve the Maxwell-Lorentz equations for hundreds of millions of particles. In the saturated regime, these simulations yield excited field spectra that correspond directly to the measured ICE spectra under diverse KSTAR and LHD regimes. At early times, comparison of simulation outputs with linear analytical theory confirms the magnetoacoustic cyclotron instability as the basic driver of ICE. [Preview Abstract] |
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BP11.00089: Numerical Study on Wave-induced Beam Ion Prompt Losses in DIII-D Tokamak Guoyong Fu, Zhichen Feng, Jia Zhu, William Heidbrink, Michael Van Zeeland A numerical study is performed on the coherent beam ion prompt losses driven by Alfven eigenmodes( AE) in DIII-D plasmas using realistic parameters and beam ion deposition profile. The synthetic signal of fast-ion loss detector(FILD) is calculated for a single AE mode. The first harmonic of the calculated FILD signal is linearly proportional to the AE amplitude with the same AE frequency in agreement with the experimental measurement. The calculated second harmonic is proportional to the square of the first harmonic for typical AE amplitudes. The coefficient of the quadratic scaling is found to be sensitive to the AE mode width. The second part of this work considers the AE drive due to coherent prompt loss. It is shown that the loss-induced mode drive is much smaller than the previous estimate and can be ignored for mode stability. [Preview Abstract] |
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BP11.00090: Electron kinetic effects on the nonlinear evolution of Reverse Shear Alfven Eigenmodes Yang Chen, Guo-Yong Fu, Scott Parker For near marginal EP driven Alfven modes the main nonlinear saturation mechanism is the trapping of resonant particles in the wave field. As the drive increases, other nonlinear effects become important. We use gyrokinetic ion/drift-kinetic electron GEM PIC simulation to examine nonlinear effects due to zonal structures and excitation of higher harmonics of the driving mode (here an n=4 RSAE). We find that, with the n=0 and n=8 perturbations included, the n=4 saturation amplitude follows the trapping scaling at low growth rates. As the growth rate increases (by increasing the beam density), the initial n=4 saturation level is modified. Both the n=0 and the n=8 perturbations are force generated by the n=4 mode via the thermal species nonlinear effects. Unlike ITG, spontaneous excitation of the zonal flows is not seen. The effect of n=0 comes from the zonal electron and ion densities, which cause fine scales in the n=4 mode structure. The Er shearing effect appears to be small. Another nonlinear damping mechanism comes from kinetic electrons. The force generated n=8 electron current gives rise to a perpendicular n=4 current due to field line bending, and this perpendicular current leads to a significant Joule heating on the electrons and damping of the driving n=4 RSAE. [Preview Abstract] |
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BP11.00091: 1D Resonance line Broadened Quasilinear (RBQ1D) code for fast ion Alfvenic relaxations and its validations Nikolai Gorelenkov, Vinicius Duarte, Mario Podesta The performance of the burning plasma can be limited by the requirements to confine the superalfvenic fusion products which are capable of resonating with the Alfvénic eigenmodes (AEs). The effect of AEs on fast ions is evaluated using the quasi-linear approach [Berk et al.,Ph.Plasmas'96] generalized for this problem recently [Duarte et al.,Ph.D.'17]. The generalization involves the resonance line broadened interaction regions with the diffusion coefficient prescribed to find the evolution of the velocity distribution function. The baseline eigenmode structures are found using the NOVA-K code perturbatively [Gorelenkov et al.,Ph.Plasmas'99]. A RBQ1D code allowing the diffusion in radial direction is presented here. The wave particle interaction can be reduced to one-dimensional dynamics where for the Alfvénic modes typically the particle kinetic energy is nearly constant. Hence to a good approximation the Quasi-Linear (QL) diffusion equation only contains derivatives in the angular momentum. The diffusion equation is then one dimensional that is efficiently solved simultaneously for all particles with the equation for the evolution of the wave angular momentum. The RBQ1D is validated against recent DIIID results [Collins et al.,PRL'16]. [Preview Abstract] |
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BP11.00092: Resonance frequency broadening of wave-particle interaction in tokamaks due to collision and microturbulence G. Meng, N. N. Gorelenkov, V. N. Duarte, R. B. White, A. Bhattacharjee The resonance width of energetic particles (EPs) and waves is crucial for the understanding and modelling for EP transport. In this work, we use ORBIT to study the broadening of resonance for DIIID shot 159243 and the parametric dependencies of the broadening width on bounce frequency, growth rate and scattering rate. With only perturbation applied, the broadening is inferred from kinetic Poincare plot. With additional scattering, the broadening width is obtained by studying particle redistribution. It is found that scattering leads to particle diffusion in phase space and increases resonance broadening significantly. With perturbation, scattering broadens resonance not only by kicking particles in and out the primary resonance island but also kicking particle across the adjacent secondary resonance island region. The redistribution process by mode trapping is much faster than scattering. The diffusion coefficient is larger at resonance island center than at the edge when perturbation is small. For DIIID, anomalous stochasticity has more important effect on the broadening compared to the collisional scattering. Comparison with RBQ and NOVA-K is in progress. This work will improve the modelling of the nonlinear process and EP transport by providing analyses for synergistic effects due to different mechanisms. [Preview Abstract] |
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BP11.00093: Frequency chirpings in Alfven continuum Ge Wang, Herb Berk, Boris Breizman, Linjin Zheng We have used a self-consistent mapping technique to describe both the nonlinear wave-energetic particle resonant interaction and its spatial mode structure that depends upon the resonant energetic particle pressure. At the threshold for the onset of the energetic particle mode (EPM), strong chirping emerges in the lower continuum close to the TAE gap and then, driven by strong continuum damping, chirps rapidly to lower frequencies in the Alfven continuum. An adiabatic theory was developed that accurately replicated the results from the simulation where the nonlinearity was only due to the EPM resonant particles. The results show that the EPM-trapped particles have their action conserved during the time of rapid chirping. This adiabaticity enabled wave trapped particles to be confined within their separatrix, and produce even larger resonant structures, that can produce a large amplitude mode far from linearly predicted frequencies. In the present work we describe the effect of additional MHD nonlinearity to this calculation. We studied how the zonal flow component and its nonlinear feedback to the fundamental frequency and found that the MHD nonlinearity doesn't significantly alter the frequency chirping response that is predicted by the calculation that neglects the MHD nonlinearity. [Preview Abstract] |
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BP11.00094: Tridimensional Thermonuclear Instability in Subignited Plasmas and on the Surface of the Pulsars A. Cardinali, B. Coppi Tridimensional modes involving an increase of the electron temperature can be excited as a result of alpha-particle heating in subignited D-T fusion burning plasmas when a nearly time- independent external source of heating is applied. The analyzed modes [1] are shown to emerge from an axisymmetric toroidal configurations and are radially localized around rational magnetic surfaces corresponding to $q(r=r_{0})=m_{0}/n_{0}$ where $ m_{0}$ and $n_{0}$ are the relevant poloidal and toroidal mode numbers. The radial width of the mode is of the order of the thermal scale distance. The mode has a rather severe damping rate, that has to be overcome by the relevant heating rate. Thus the temperature range to be considered is that where the D-T plasma reactivity undergoes a relatively large increase as a function of temperature. This kind of theory has been applied to the plasmas that are envisioned to be associated with surface of pulsar and be subjects to (spatially) inhomogenous thermonuclear burning. \\ [1] B. Coppi, et al. $\it{Nucl. Fus}$., $\bf{55}$ 053011 (2015). [Preview Abstract] |
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BP11.00095: Magnetic Reconnection Driven by Thermonuclear Burning R. Gatto, B. Coppi Considering that fusion reaction products (e.g. $\alpha$-particles) deposit their energy on the electrons, the relevant thermal energy balance equation is characterized by a fusion source term, a relatively large longitudinal thermal conductivity and an appropriate transverse thermal conductivity. Then, looking for modes that are radially localized around rational surfaces [1], reconnected field configurations are found that can be sustained by the electron thermal energy source due to fusion reactions. Then this process can be included in the category of endogenous reconnection processes and may be viewed as a form of the thermonuclear instability that can develop in an ignited inhomogeneous plasma. A complete analysis of the equations supporting the relevant theory is reported.\\ 1. B. Coppi, et al. $\it{Nucl. Fus}. {\bf55}$, 05311 (2015). [Preview Abstract] |
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BP11.00096: OTHER CONFINEMENT CONCEPTS AND NEXT STEPS |
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BP11.00097: Initial operation of the Lockheed Martin T4B experiment M.L. Garrett, A. Blinzer, F. Ebersohn, S. Gucker, J. Heinrich, C. Lohff, T. McGuire, N. Montecalvo, A. Raymond, J. Rhoads, P. Ross, B. Sommers, E. Strandberg, R. Sullivan, J. Walker The T4B experiment is a linear, encapsulated ring cusp confinement device, designed to develop a physics and technology basis for a follow-on high beta ($\beta \sim 1$) machine. The experiment consists of 13 magnetic field coils (11 external, 2 internal), to produce a series of on-axis field nulls surrounded by modest magnetic fields of up to 0.3 T. The primary plasma source used on T4B is a lanthanum hexaboride (LaB$_6$) cathode, capable of coupling over 100 kW into the plasma. Initial testing focused on commissioning of components and integration of diagnostics. Diagnostics include both long and short wavelength interferometry, bolometry, visible and X-ray spectroscopy, Langmuir and B-dot probes, Thomson scattering, flux loops, and fast camera imagery. Low energy discharges were used to begin validation of physics models and simulation efforts. Following the initial machine check-out, neutral beam injection (NBI) was integrated onto the device. Detailed results will be presented. \copyright\,2017 Lockheed Martin Corporation. All Rights Reserved. [Preview Abstract] |
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BP11.00098: An overview of optical diagnostics developed for the Lockheed Martin compact fusion reactor Bradley Sommers, Anthony Raymond, Sarah Gucker The T4B experiment is a linear, encapsulated ring cusp confinement device, designed to develop a physics and technology basis for a follow-on high beta machine as part of the compact fusion reactor program. Toward this end, a collection of non-invasive optical diagnostics have been developed to investigate confinement, neutral beam heating, and source behavior on the T4B device. These diagnostics include: (1) a multipoint Thomson scattering system employing a 532 nm Nd:YAG laser and high throughput spectrometer to measure 1D profiles of electron density and temperature, (2) a dispersion interferometer utilizing a continuous-wave CO2 laser (10.6 $\mu $m) to measure time resolved, line-integrated electron density, and (3) a bolometer suite utilizing four AXUV photodiodes with 64 lines of sight to generate 2D reconstructions of total radiative power and soft x-ray emission (via beryllium filters). An overview of design methods, including laser systems, detection schemes, and data analysis techniques is presented as well as results to date. [Preview Abstract] |
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BP11.00099: Neutral Beam Development for the Lockheed Martin Compact Fusion Reactor Frans Ebersohn, Regina Sullivan The Compact Fusion Reactor project at Lockheed Martin Skunk Works is developing a neutral beam injection system for plasma heating. The neutral beam plasma source consists of a high current lanthanum hexaboride (LaB6) hollow cathode which drives an azimuthal cusp discharge similar to gridded ion thrusters. The beam is extracted with a set of focusing grids and is then neutralized in a chamber pumped with Titanium gettering. The design, testing, and analyses of individual components are presented along with the most current full system results. The goal of this project is to advance in-house neutral beam expertise at Lockheed Martin to aid in operation, procurement, and development of neutral beam technology. \copyright 2017 Lockheed Martin Corporation. All Rights Reserved. [Preview Abstract] |
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BP11.00100: Simulations in support of the T4B experiment Artan Qerushi, Patrick Ross, Chriss Lohff, Anthony Raymond, Niccolo Montecalvo Simulations in support of the T4B experiment are presented. These include a Grad-Shafranov equilibrium solver and equilibrium reconstruction from flux-loop measurements, collision radiative models for plasma spectroscopy (determination of electron density and temperature from line ratios) and fast ion test particle codes for neutral beam - plasma coupling. \copyright 2017 Lockheed Martin Corporation. All Rights Reserved. [Preview Abstract] |
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BP11.00101: Magnetic Guarding: Experimental and Numerical Results Jonathon Heinrich, Gabriel Font, Michael Garrett, D. Rose, T. Genoni, D. Welch, Thomas McGuire The magnetic field topology of Lockheed Martin's Compact Fusion Reactor (CFR) concept requires internal magnetic field coils. Internal coils for similar devices have leveraged levitating coils or coils with magnetically guarded supports. Magnetic guarding of supports has been investigated for multipole devices (theoretically and experimentally) without conclusive results [1-4]. One outstanding question regarding magnetic guarding of supports is the magnitude and behavior of secondary plasma drifts resulting from magnetic guard fields (grad-B drifts, etc). We present magnetic-implicit PIC modeling results and preliminary proof of concept experimental results on magnetic guarding of internal-supports and the subsequent reduction in total plasma losses. \copyright 2017 Lockheed Martin Corporation. All Rights Reserved. [1] B. Lehnert,\textit{ Nature}. 181, 331 (1958); [2] M. Rusbridge, \textit{Plasma Phys}. 13, 977 (1971); [3] H. Forsen, D. Kerst, D. Lencioni, D. Meade, F. Mills, A. Molvik, J. Schmidt, J. Sprott, K. Syman, \textit{Plasma Phys. And Cont. Nucl. Fus. Res., IAEA.} 24, 1, 313 (1969); [4] L. Burkhardt, J. DiMarco, J. Hammel, R. Henson, H. Karr, \textit{Phys. Fluids. }11, 1562 (1968). [Preview Abstract] |
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BP11.00102: Simulation of High-Beta Plasma Confinement Gabriel Font, Dale Welch, Robert Mitchell, Thomas McGuire The Lockheed Martin Compact Fusion Reactor concept utilizes magnetic cusps to confine the plasma. In order to minimize losses through the axial and ring cusps, the plasma is pushed to a high-beta state. Simulations were made of the plasma and magnetic field system in an effort to quantify particle confinement times and plasma behavior characteristics. Computations are carried out with LSP using implicit PIC methods. Simulations of different sub-scale geometries at high-Beta fusion conditions are used to determine particle loss scaling with reactor size, plasma conditions, and gyro radii. \copyright 2017 Lockheed Martin Corporation. All Rights Reserved. [Preview Abstract] |
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BP11.00103: Plasma Source Development Jonathan Walker, Jonathon Heinrich, Gabriel Font, Frans Ebersohn, Michael Garrett A 100 kW class lanthanum-hexaboride plasma source is under continuing development for the Lockheed Martin Compact Fusion Reactor program. The current experiment, T4B, has become a test bed for plasma source operation with the goal of creating a high density plasma target for neutral beam heating. We present operation and performance of different plasma source geometries, results of plasma source coupling, and future plasma source development plans. \copyright 2017 Lockheed Martin Corporation. All Rights Reserved. [Preview Abstract] |
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BP11.00104: Advanced particle-in-cell simulation techniques for modeling the Lockheed Martin Compact Fusion Reactor Dale Welch, Gabriel Font, Robert Mitchell, David Rose We report on particle-in-cell developments of the study of the Compact Fusion Reactor. Millisecond, two and three-dimensional simulations (cubic meter volume) of confinement and neutral beam heating of the magnetic confinement device requires accurate representation of the complex orbits, near perfect energy conservation, and significant computational power. In order to determine initial plasma fill and neutral beam heating, these simulations include ionization, elastic and charge exchange hydrogen reactions. To this end, we are pursuing fast electromagnetic kinetic modeling algorithms including a two implicit techniques and a hybrid quasi-neutral algorithm with kinetic ions. The kinetic modeling includes use of the Poisson-corrected direct implicit,[1] magnetic implicit,[2] as well as second-order cloud-in-cell techniques. The hybrid algorithm, ignoring electron inertial effects, is two orders of magnitude faster than kinetic but not as accurate with respect to confinement. The advantages and disadvantages of these techniques will be presented. [1] D. R. Welch, D. V. Rose, B. V. Oliver, and R. E. Clark, Nucl. Inst. Meth. Phys. Res. A 464, 134 (2001). [2] T. C. Genoni, R. E. Clark and D. R. Welch, The Open Plasma Physics Journal 3, 36 (2010). [Preview Abstract] |
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BP11.00105: A high fusion power gain tandem mirror T.K. Fowler, R.W. Moir, T.C. Simonen Utilizing advances in high field superconducting magnet technology and microwave gyrotrons we illustrate the possibility of a high power gain (Q = 10-20) tandem mirror fusion reactor$^1$. Inspired by recent Gas Dynamic Trap (GDT) achievements$^2$ we employ a simple axisymmetric mirror magnet configuration. We consider both DT and cat. DD fuel options that utilize existing as well as future technology development. We identify subjects requiring further study such as hot electron physics, trapped particle modes and plasma startup.\\ \\ $[1]$T.K. Fowler, R.W. Moir and T.C. Simonen, Nuclear Fusion 57 (2017) 056014\\ $[2]$P.A. Bagryansky, et.al., Phys. Rev. Letters 114 (2015) 205001 [Preview Abstract] |
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BP11.00106: A design of the MHD stable axisymmetric mirror Isao Katanuma The PRC (Plasma Research Center GAMMA10) group is planning the construction of next linear device to perform the divertor experiment by using its endloss flux since last year. One candidate device is considered to be a single axisymmetric mirror. The reasons are that the axisymmetric mirror has attractive features on a collaboration with the mirror community and a future mirror fusion device as well as the construction costs of pancake coils are lower than the base-ball coils. The axisymmetric mirror stabilizes the interchange modes with the help of large $\mathrm{E}\times\mathrm{B}$ azimuthal velocity shear flow surrounding the core plasma confining region. This flow shear is realized by making the radial electric field, which is similar to the vortex confinement of recent GDT[1]. Although this flow shear induces the Kelvin-Helmholtz instability, it is found to cause not so large radial transport when the magnitude of the flow shear is strong. The axisymmetric mirror also stabilizes the interchange modes with the help of large ion endloss flux just like gas dynamic trap (GDT). Here the large endloss flux is needed to perform the divertor experiment. [1] A.Beklemishev, et.al., Fusion Sci. Tech. 57, 351 (2010). [Preview Abstract] |
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BP11.00107: A GDT-based fusion neutron source for academic and industrial applications J. K. Anderson, C. B. Forest, V. V. Mirnov, E. E. Peterson, R. Waleffe, J. Wallace, R. W. Harvey The design of a fusion neutron source based on the gas dynamic trap (GDT) configuration is underway. The motivation is both the ends and the means. There are immediate applications for neutrons including medical isotope production and actinide burners. Taking the next step in the magnetic mirror path will leverage advances in high-temperature superconducting magnets and additive manufacturing in confining a fusion plasma, and both the technological and physics bases exist. Recent breakthrough results at the GDT facility in Russia demonstrate stable confinement of a beta\textasciitilde 60{\%} mirror plasma at high Te (\textasciitilde 1keV). These scale readily to a fusion neutron source with an increase in magnetic field, mirror ratio, and ion energy. Studies of a next-step compact device focus on calculations of MHD equilibrium and stability, and Fokker-Planck modeling to optimize the heating scenario. The conceptualized device uses off-the-shelf MRI magnets for a 1 T central field, REBCO superconducting mirror coils (which can currently produce fields in excess of 30T), and existing 75 keV NBI and 140 GHz ECRH. High harmonic fast wave injection is damped on beam ions, dramatically increasing the fusion reactivity for an incremental bump in input power. MHD stability is achieved with the vortex confinement scheme, where a biasing profile imposes optimal ExB rotation of the plasma. Liquid metal divertors are being considered in the end cells. Work supported by the Wisconsin Alumni Research Foundation. [Preview Abstract] |
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BP11.00108: How much does a tokamak reactor cost? J. Freidberg, A. Cerfon, S. Ballinger, J. Barber, A. Dogra, W. McCarthy, L. Milanese, T. Mouratidis, W. Redman, A. Sandberg, D. Segal, R. Simpson, C. Sorensen, M. Zhou The cost of a fusion reactor is of critical importance to its ultimate acceptability as a commercial source of electricity. While there are general rules of thumb for scaling both overnight cost and levelized cost of electricity the corresponding relations are not very accurate or universally agreed upon. We have carried out a series of scaling studies of tokamak reactor costs based on reasonably sophisticated plasma and engineering models. The analysis is largely analytic, requiring only a simple numerical code, thus allowing a very large number of designs. Importantly, the studies are aimed at plasma physicists rather than fusion engineers. The goals are to assess the pros and cons of steady state burning plasma experiments and reactors. One specific set of results discusses the benefits of higher magnetic fields, now possible because of the recent development of high T rare earth superconductors (REBCO); with this goal in mind, we calculate quantitative expressions, including both scaling and multiplicative constants, for cost and major radius as a function of central magnetic field. [Preview Abstract] |
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BP11.00109: From Lawson to Burning Plasmas: a Multi-Fluid Approach Luca Guazzotto, Riccardo Betti The Lawson criterion [1], easily compared to experimental parameters, gives the value for the triple product of plasma density, temperature and energy confinement time needed for the plasma to ignite. Lawson's inaccurate assumptions of 0D geometry and single-fluid plasma model were improved in recent work, where 1D geometry and multi-fluid (ions, electrons and alphas) physics were included in the model, accounting for physical equilibration times and different energy confinement times between species [2]. A much more meaningful analysis than Lawson's for current and future experiment would be expressed in terms of burning plasma state (Q=5, where Q is the ratio between fusion power and heating power). Minimum parameters for reaching Q=5 are calculated based on experimental profiles for density and temperatures and can immediately be compared with experimental performance by defining a no-alpha pressure. This is done in terms of the pressure that the plasma needs to reach for breakeven once the alpha heating has been subtracted from the energy balance. These calculations can be applied to current experiments and future burning-plasma devices. [1] J. D. Lawson, Proc. Phys. Soc. London Sect. B 70, 6 (1957) [2] L. Guazzotto and R. Betti, to appear in Phys. Plasmas [Preview Abstract] |
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BP11.00110: ICF MEASUREMENT AND DIAGNOSTIC TECHNIQUES |
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BP11.00111: Feasibility of transition radiation diagnostic for hot electrons generated in indirect-drive experiment Yaoyuan Liu, Jian Zheng, Guangyue Hu, Dong Yang, Yonggang Liu, Sanwei Li, Xianhua Jiang, Zhebin Wang, Huan Zhang, Xianshi Peng, Feng Wang, Shaoen Jiang, Yongkun Ding In the experiment of indirect-drive laser fusion, parameter instabilities like stimulated Raman scattering (SRS) can generate abundant hot electrons, which can preheat fuel and degrade target gain. Hot electrons are usually investigated through their bremsstrahlung measured with filter-fluoresce (FF) X-ray spectrometer. In this presentation, we propose the feasibility of studying hot electrons by detecting the transition radiation (TR) emitted when energetic electrons pass through the outer surface of a hohlraum. With aid of Monte Carlo simulations, we find that the intensity of optical TR is equivalent to that of 0.2 eV black-body radiation (BR) in the typical experiments of the SG-III prototype facility with the energy of \textasciitilde 10 kJ during 1 ns. Therefore, optical transition could be a candidate for the measurement of hot electrons without preheating. However, our simulations shows that the outer surface can be heated to 0.55 eV due to the hot electrons, leading to much brighter BR than the TR. In fact, our streaked optical pyrometer indicates that the preheating temperature reaches 0.7-1.0 eV. Hence it would be impossible to diagnose the hot electrons through optical TR. Our calculations show that it is plausibly feasible to detect the TR in the region of far infrared or THz. [Preview Abstract] |
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BP11.00112: First experiment on LMJ facility : pointing and synchronisation qualification. Olivier Henry, Didier Raffestin, Dominique Bretheau, Michel Luttmann, Herve Graillot, Michel Ferri, Frederic Seguineau, Emmanuel Bar, Loic Patissou, Philippe Canal, Françoise Sautarel, Yves Tranquille-Marques The LMJ (Laser mega Joule) facility at the CESTA site (Aquitaine, France) is a tool designed to deliver up to 1.2 MJ at 351 nm for plasma experiments. The experiment system will include 11 diagnostics: UV and X energy balances, imagers (Streak and stripe camera, CCD), spectrometers, and a Visar/pyrometer. The facility must be able to deliver, within the hour following the shot, all the results of the plasma diagnostics, alignment images and laser diagnostic measurements. These results have to be guaranteed in terms of conformity to the request and quality of measurement. The end of 2016 was devoted to the qualification of system pointing on target and synchronization within and between beams. The shots made with two chains (divided in 4 quads -- 8 laser beams) have achieved 50 $\backslash $textmu m of misalignment accuracy (chain and quad channel) and a synchronization accuracy in the order of 50 ps . The performances achieved for plasma diagnostic (in the order of less 100 $\backslash $textmu m of alignment and timing accuracy less than 150 ps) comply with expectations. At the same time the first automatic sequences were tested. They allowed a shot on target every 6h:30 and in some case twice a day by reducing preparation actions, leading to a sequence of 4h:00. [Preview Abstract] |
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BP11.00113: Abstract Withdrawn
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BP11.00114: A Novel Peak Load Current Measurement for Magneto-Inertial-Fusion Targets Mark Hess, Kyle Peterson, David Ampleford, Brian Hutsel, Christopher Jennings, Daniel Dolan, William Stygar, Matthew Gomez, Matthew Martin, Grafton Robertson, Daniel Sinars We have developed a novel method for measuring the peak load current (\textgreater 15 MA) delivered to MagLIF targets on the Z pulsed power facility at Sandia National Laboratories using a Photonic Doppler Velocimetry (PDV) diagnostic in the final power feed section. Our diagnostic features a 600 micron thick aluminum PDV flyer, which is sufficiently thick to minimize the effects of magnetic diffusion in the flyer. In this regime, we can relate the peak velocity of the flyer to a peak magnetic pressure, and hence, peak load current, since the measured peak velocity is relatively insensitive to typical variability in MagLIF load current shapes. This allows for a quick analysis (\textless 1 hour) in determining the peak MagLIF load current. We also demonstrate the agreement between measured peak load currents from this diagnostic and circuit models of Z machine, which have been developed at Sandia. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U. S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
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BP11.00115: Utilization of Neutron Bang-time CVD diamond detectors at the Z Accelerator Gordon Chandler, Kelly Hahn, Carlos Ruiz, Brent Jones, Perry Alberto, Jose Torres, Matthew Gomez, Eric Harding, Adam Harvey-Thompson, Mark Hess, Patrick Knapp, Gary Cooper, Jedediah Styron, Ken Moy, Ian Mckenna, Vladimir Glebov, David Fittinghoff, Mark J. May, Lucas Snyder We are utilizing Chemical Vapor Deposited (CVD) Diamond detectors at \textasciitilde 2.3 meters on the Z accelerator to infer neutron bang-times from Magnetized Liner Inertial Fusion (MagLIF) sources yielding up to 3e12 DD neutrons and to bound the neutron time history of Deuterium Gas Puff loads producing 5e13 DD neutrons. The current implementation of the diagnostic and initial results will be shown as well as our future plans for the diagnostic. [Preview Abstract] |
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BP11.00116: Obtaining the neutron time-of-flight instrument response function for a single D-T neutron utilizing n-alpha coincidence from the d(t, $\alpha )$n nuclear reaction . Jedediah Styron, Carlos Ruiz, Kelly Hahn, Gary Cooper, Gordon Chandler, Brent Jones, Bruce McWatters, Jenny Smith, Jeremy Vaughan A measured neutron time-of-flight (nTOF) signal is a convolution of the neutron reaction history and the instrument response function (IRF). For this work, the IRF was obtained by measuring single, D-T neutron events by utilizing n-alpha coincidence. The d(t, $\alpha )$n nuclear reaction was produced at Sandia National Laboratories' Ion Beam Laboratory using a 300-keV Cockroft-Walton generator to accelerate a 2-$\mu $A beam, of 175-keV D$+$ ions, into a stationary, 2.6-$\mu $m, ErT2 target. Comparison of these results to those obtained using cosmic-rays and photons will be discussed. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. [Preview Abstract] |
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BP11.00117: Characterizing the Degree of Fuel Magnetization for MagLIF Using Neutron Diagnostics K.D. Hahn, G.A. Chandler, P.F. Schmit, P.F. Knapp, S.B. Hansen, E. Harding, C.L. Ruiz, B. Jones, M.R. Gomez, D.J. Ampleford, J.A. Torres, P.J. Alberto, G.W. Cooper, J.D. Styron We are studying Magnetized Liner Inertial Fusion sources which utilize deuterium fuel and produce up to 4e12 primary DD and 5e10 secondary DT neutrons. For this concept, magnetizing the fuel can relax the stagnation pressures and densities required for ignition by insulating the hot fuel and confining the charged fusion products. The degree of magnetization of the fuel at stagnation is quantified using secondary DT neutron spectral measurements in the axial and radial directions and is also related to the ratio of the secondary DT yield to the primary DD yield. Measurements have confirmed that charged fusion products are strongly magnetized, as indicated by the product of the magnetic field and the fuel radius, to \textasciitilde 0.4 MG-cm. We present new results that compare the degree of fuel magnetization inferred from spectral and yield measurements. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. [Preview Abstract] |
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BP11.00118: The Magnetic Recoil Spectrometer for time-resolved neutron measurements (MRSt) at the NIF C.E. Parker, J.A. Frenje, C.W. Wink, M. Gatu Johnson, B. Lahmann, C.K. Li, F.H. Seguin, R.D. Petrasso, T.J. Hilsabeck, J.D. Kilkenny, R. Bionta, D.T. Casey, H.Y. Khater, C.J. Forrest, V.YU. Glebov, C. Sorce, J.D. Hares, O.H.W. Siegmund The next-generation Magnetic Recoil Spectrometer, called MRSt, will provide time-resolved measurements of the DT-neutron spectrum. These measurements will provide critical information about the time evolution of the fuel assembly, hot-spot formation, and nuclear burn in Inertial Confinement Fusion (ICF) implosions at the National Ignition Facility (NIF). The neutron spectrum in the energy range 12-16 MeV will be measured with high accuracy (\textasciitilde 5{\%}), unprecedented energy resolution (\textasciitilde 100 keV) and, for the first time ever, time resolution (\textasciitilde 20 ps). An overview of the physics motivation, conceptual design for meeting these performance requirements, and the status of the offline tests for critical components will be presented. This work was supported in part by the U.S. DOE, LLNL, and LLE. [Preview Abstract] |
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BP11.00119: Gamma-based Measurement of ``Dark Mix'' in ICF Capsules Kevin Meaney, H Herrmann, YH Kim, AB Zylstra, H Geppert-Kleinrath, NM Hoffman, AS Yi Mix of capsule ablator material into the fusion fuel is a source of yield degradation in inertial confinement fusion. Jetting or chunk mix, such as the elusive ``meteors'' that have been observed at NIF, can be difficult to diagnose because the chunks may not get hot enough to excite dopant x-rays, nor atomized enough for separated-reactants to fuse. Using the gamma reaction history (GRH-6m) diagnostic, (n,n') gammas from strategically placed carbon layer within a beryllium capsule gives a measure of the time-resolved areal density of this carbon during the burn and hence an indication of the compression and spatial distribution of this layer. As the carbon moves further from the fuel, the areal density nominally decreases as 1/r$^{\mathrm{2}}$ for unablated material. However, mix of this carbon into the cold dense fuel layer or hot spot will have a significant effect on the carbon gamma signal.~Different types of mix (e.g., jetting, Rayleigh-Taylor fingers, diffusive, \textellipsis ) as well as features that can seed this mix (eg., tents, fill,\textellipsis ) will be discussed along with their expected effect on the carbon signal. The design for upcoming OMEGA shots, which will demonstrate this technique, and the potential for use on the NIF will be presented. [Preview Abstract] |
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BP11.00120: The Mini Orange Spectrometer (MOS) for Stellar and Big-Bang Nucleosynthesis studies at OMEGA and the National Ignition Facility G.D. Sutcliffe, J.A. Frenje, M. Gatu Johnson, C.K. Li, C. Parker, R. Simpson, H. Sio, F.H. Seguin, R.D. Petrasso, A. Zylstra A compact and highly efficient Mini Orange Spectrometer (MOS) is being designed for measurements of energy spectra of protons and alphas in the range of 1-12 MeV in experiments at the OMEGA laser facility and the National Ignition Facility (NIF). The MOS will extend charged-particle spectrometry at these laser facilities to lower energies (\textless 5 MeV) and lower yields (\textless 5\texttimes 10$^{\mathrm{8}})$ than current instrumentation allows. This new spectrometer will enable studies of low-probability stellar nucleosynthesis reactions, including the $^{\mathrm{3}}$He$+^{\mathrm{3}}$He reaction that is part of the solar proton-proton chain. Its unique capabilities will also be exploited in other basic science experiments, including studies of stopping power in ICF-relevant plasmas, astrophysical shocks and kinetic physics. The MOS design achieves high efficiency by maximizing the solid angle of particle acceptance. The optimization of the MOS design uses simulated magnetic fields and particle tracing. Performance requirements of the MOS system, including desired detection efficiencies and energy resolution, are discussed. This work was supported in part by the U.S. DoE, LLNL, and LLE. [Preview Abstract] |
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BP11.00121: High resolution spectrometer concepts for high temperature EXAFS measurements and 1D imaging of ignition capsules on NIF K. W. Hill, M. Bitter, L. Gao, B. Kraus, P. C. Efthimion, M. B. Schneider, D. B. Thorn, F. Coppari, Y. Ping, K. L. Killebrew, A. G. MacPhee, R. L. Kauffman, P. Beiersdorfer X-ray spectrometer concepts for two applications on NIF are being studied. An Extended X-ray Absorption Fine Structure (EXAFS) spectrometer will determine temperature at high pressure of dynamically compressed materials, by measuring K and L3 absorption edges at energies from 7112 to 18000 eV. A Johann geometry with spherically or toroidally bent crystals will avoid source-size broadening for spectral resolving power (E/$\Delta $E) of \textasciitilde 6000. Energy-range selection is by crystal choice. The second is a 1D imaging spectrometer to measure the spatial distribution of plasma parameters to study stagnation of ignition capsules, based on either spherical or conical crystals with large spatial magnification. The desired spatial resolution is 5 $\mu $m. Predicted performance and prototype spectrometer measurements will be presented. [Preview Abstract] |
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BP11.00122: The MIT HEDP Accelerator Facility for Diagnostic Development for OMEGA, Z, and the NIF H. Sio, M. Gatu Johnson, A. Birkel, E. Doeg, R. Frankel, N.V. Kabadi, B. Lahmann, M. Manzin, R.A. Simpson, C.E. Parker, G.D. Sutcliffe, C. Wink, J.A. Frenje, C.K. Li, F.H. Seguin, R.D. Petrasso, R. Leeper, K. Hahn, C.L. Ruiz, T.C. Sangster, T. Hilsabeck The MIT HEDP Accelerator Facility utilizes a 135-keV, linear electrostatic ion accelerator; DT and DD neutron sources; and two x-ray sources for development and characterization of nuclear diagnostics for OMEGA, Z, and the NIF. The accelerator generates DD and D$^{\mathrm{3}}$He fusion products through the acceleration of D$^{\mathrm{+}}$ ions onto a $^{\mathrm{3}}$He-doped Erbium-Deuteride target. Accurately characterized fusion product rates of around 10$^{\mathrm{6}}$ s$^{-}^{\mathrm{1}}$ are routinely achieved. The DT and DD neutron sources generate up to 6\texttimes 10$^{\mathrm{8}}$ and 1\texttimes 10$^{\mathrm{7}}$ neutrons/s, respectively. One x-ray generator is a thick-target W source with a peak energy of 225 keV and a maximum dose rate of 12 Gy/min; the other uses Cu, Mo, or Ti elemental tubes to generate x-rays with a maximum energy of 40 keV. Diagnostics developed and calibrated at this facility include CR-39-based charged-particle spectrometers, neutron detectors, and the particle Time-Of-Flight (pTOF) and Magnetic PTOF CVD-diamond-based bang time detectors. The accelerator is also a valuable hands-on tool for graduate and undergraduate education at MIT. This work was supported in part by the U.S. DoE, SNL, LLE and LLNL. [Preview Abstract] |
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BP11.00123: Determining Light Decay Curves in a Plastic Scintillator using Cosmic Ray Muons Praveen Wakwella, Sarah Mandanas, John Wilson, Hannah Visca, Stephen Padalino, T. Craig Sangster, Sean P. Regan Plastic scintillators are used in ICF research to measure neutron energies via their time of flight (nToF). The energy resolution and sensitivity of an nToF system is directly correlated with the scintillation decay time of the plastic. To decrease the decay time, some scintillators are quenched with oxygen. Consequently, they become less efficient at producing light. As time passes, oxygen defuses out of the scintillator this in turn increases light production and the decay time. Mono-energetic calibration neutrons produced at accelerator facilities can be used to monitor the decreased oxygen content, however this is a time consuming process and requires that the scintillators be removed from the ICF facilities on a regular basis. Here, a possible method for cross calibrating accelerator neutrons with cosmic ray muons is presented. This method characterizes the scintillator with accelerator-generated neutrons and then cross calibrates them with cosmic ray muons. Once the scintillators are redeployed at the ICF facility the oxygen level can be regularly monitored using muons in situ. [Preview Abstract] |
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BP11.00124: Dual-Wavelength Interferometry and Light Emission Study for Experimental Support of Dual-Wire Ablation Experiments Andrew Hamilton, James Caplinger, Vladimir Sotnikov, Gennady Sarkisov, John Leland In the Plasma Physics and Sensors Laboratory, located at Wright Patterson Air Force Base, we utilize a pulsed power source to create plasma through a wire ablation process of metallic wires. With a parallel arrangement of wires the azimuthal magnetic fields generated around each wire, along with the Ohmic current dissipation and heating occurring upon wire evaporation, launch strong radial outflows of magnetized plasmas towards the centralized stagnation region. It is in this region that we investigate two phases of the wire ablation process. Observations in the first phase are collsionless and mostly comprised of light ions ejected from the initial corona. The second phase is observed when the wire core is ablated and heavy ions dominate collisions in the stagnation region. In this presentation we will show how dual-wavelength interferometric techniques can provide information about electron and atomic densities from experiments. Additionally, we expect white-light emission to provide a qualitative confirmation of the instabilities observed from our experiments. [Preview Abstract] |
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BP11.00125: LASER-PLASMA INSTABILITIES |
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BP11.00126: Magnetic field generation in finite beam plasma system Atul Kumar, Chandrasekhar Shukla, Bhavesh Patel, Amita Das, Predhiman Kaw The magnetic field generation is an important issue in a variety of contexts. In a beam plasma system, it is typically believed that the Weibel destabilization process causes the generation of magnetic fields at the electron skin depth scales. It has recently been shown, however, that a finite transverse size of the beam leads to the generation of the magnetic field at the long scale length of the beam (arXiv.org,1704.00970v1 [physics.plasm-ph], 2017). This has been attributed to a new instability associated with the Finite Boundary Size (FBS) operative in this context. In a realistic situation, the beam in addition to having a finite transverse extent would also have a finite temporal width. Keeping this in view in the present work a finite longitudinal extent of the beam has also been considered. Particle - In - Cell (PIC) simulations using OSIRIS were conducted which illustrates that in this case too the FBS instability is the first one to appear which is followed up by the KH at the edge and the Weibel in the bulk region. The magnetic field power spectrum has been observed to maximize at the longest scale of the beam size, as expected. In addition, we observe the relativistic shock formation, the beam focussing at the front and wake like structures in this case. [Preview Abstract] |
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BP11.00127: A Concept for Measuring Electron Distribution Functions Using Collective Thomson Scattering A.L. Milder, D.H. Froula A.B. Langdon\footnote{A. B. Langdon, Phys. Rev. Lett. \textbf{44}, 575 (1980).} proposed that stable non-Maxwellian distribution functions are realized in coronal inertial confinement fusion plasmas via inverse bremsstrahlung heating. For ${Zv_{\mbox{osc}}^{2} } \mathord{\left/ {\vphantom {{Zv_{\mbox{osc}}^{2} } {v_{\mbox{th}}^{2} >1,}}} \right. \kern-\nulldelimiterspace} {v_{\mbox{th}}^{2} >1,}$ the inverse bremsstrahlung heating rate is sufficiently fast to compete with electron--electron collisions. This process preferentially heats the subthermal electrons leading to super-Gaussian distribution functions. A method to identify the super-Gaussian order of the distribution functions in these plasmas using collective Thomson scattering will be proposed. By measuring the collective Thomson spectra over a range of angles the density, temperature and super-Gaussian order can be determined. This is accomplished by fitting non-Maxwellian distribution data with a super-Gaussian model; in order to match the density and electron temperature to within 10{\%}, the super-Gaussian order must be varied. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
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BP11.00128: Modelling of heat flux driven return current instability and ion acoustic turbulence Wojciech Rozmus, M. Sherlock, A.V. Brantov, V. Yu. Bychenkov Hot plasmas with strong temperature gradients in inertial confinement fusion (ICF) experiments are examined for ion acoustic instabilities produced by electron heat flux. Return current instability (RCI) due to neutralizing current of cold electrons arising in response to large electron heat flux has been considered. First linear threshold and growth rates are derived in the nonlocal regime of the thermal transport. They are compared with results of Vlasov-Fokker-Planck (VFP) simulations in one spatial dimensions. Very good agreement has been found between kinetic VFP simulations and linear theory of the RCI. Quasi stationary state of ion acoustic turbulence produced by the RCI is achieved in VFP simulations. A saturation of the RCI involves heating of ions in the tail of the ion distribution function, convection of the enhanced ion acoustic fluctuations from the unstable region of the plasma and anomalous electron resistivity. Further evolution of the ion acoustic turbulence and its effects on the absorption and transport are also discussed. [Preview Abstract] |
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BP11.00129: Detrimental Plasma Memory Effect Build Up Locally and Nonlinearly, as well as Globally and Fractally in RPP/SSD beams Subdued by Using STUD Pulses Anas Bouzid, Bradley Shadwick, Stefan Hüller, Bedros Afeyan We show how long time correlations build up in space and time locally in a single hot spot, as well as globally through many tranches of hot spots for backscattering instabilities. STUD pulses remove such obstacles by combatting the memory build up effects directly. Experiments are proposed that can test these predictions. Statistical optical tools are used to characterize the behavior of scattered light fields re-amplifying in various stages and spreading in angular reach fractally. An analytic model is proposed capturing these effects. [Preview Abstract] |
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BP11.00130: Particle-in-Cell Simulation of Laser Plasma Interactions in Multiple Speckles with Temporal Bandwidth Han Wen, Benjamin Winjum, Frank Tsung, Kyle Miller, Adam Tableman, Warren Mori The widely used laser-smoothing techniques introduce small-scale structures (speckles) with higher-than-average intensities. The stimulated Raman scattering (SRS) instability is more likely to growth in the intense speckles. On the other hand, if the temporal bandwidth of the laser is comparable to the growth rate of SRS, the SRS may be reduced. To study the interaction of SRS and time-varying laser speckles in kinetic regimes, a general laser antenna has been implemented in particle-in-cell (PIC) code OSIRIS. This antenna is capable of modeling smoothing by spectral dispersion~(SSD), induced spatial incoherence~(ISI), and spike train of uneven duration and delay (STUD) pulse. Preliminary results of SRS affected by different laser-smoothing techniques are discussed. This Work is supported by NSF and DOE. [Preview Abstract] |
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BP11.00131: Fluid modeling on three dimensional two plasmon decay instabilities and stimulated Raman scattering using FLAME-MD Rui Yan, Shihui Cao, Zhenhua Wan, Guangyue Hu, Jian Zheng, Liang Hao, Wenda Liu, Chuang Ren We push our FLAME project forward with a newly developed code \textit{FLAME-MD} (Multi-Dimensional) based on the fluid model presented in Ref.[1]. Simulations are performed to study two plasmon decay (TPD) instabilities and stimulated Raman scattering (SRS) in three dimensions (3D) with parameters relevant to ICF. 3D effects on the growth of TPD and SRS, including laser polarizations and multi beam configurations, are studied. [1] L. Hao et al., Phys. Plasmas \textbf{24}, 062709 (2017) [Preview Abstract] |
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BP11.00132: Hot electron reduction in two-plasmon-decay by magnetic fields Wenda Liu, Chuang Ren We performed PIC simulations on two-plasmon-decay (TPD) and associated hot electron generation under perpendicular magnetic fields of 10 and 100 T. TPD linear growth and saturation levels are not significantly changed. Hot electron generation is significantly reduced when B$=$100 T but not when B$=$10 T. The reduction is due to disruption of the staged acceleration of hot electron through their gyro-motion. The reduction affects the low-energy hot electrons more than high-energy ones. Magnetic field generation mechanisms in target corona will also be discussed. [Preview Abstract] |
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BP11.00133: The effect of magnetic fields on the kinetic evolution of nonlinear electron plasma waves and stimulated Raman scattering B. J. Winjum, A. Tableman, F. S. Tsung, W. B. Mori Nonlinear wave-particle interactions can significantly affect the evolution of stimulated Raman scattering (SRS) for ICF-relevant parameters. An imposed magnetic field can alter the dynamics of these interactions and thereby the dynamics of SRS, altering the instability threshold and saturation. Particles resonant with an SRS-generated electron plasma wave can be rotated in velocity space, disrupting the nonlinear damping of electron plasma waves and changing the kinetically inflated SRS threshold. Resonant particles can also be rotated in physical space, changing the transverse kinetic dissipation of electron plasma waves and restricting trapped particle motion both within a single laser speckle as well as between neighboring laser speckles. We show PIC simulations of driven multi-dimensional electron plasma waves in the presence of an external field and illustrate how their nonlinear evolution is altered, particularly with regard to the dynamical behavior that can impact SRS. [Preview Abstract] |
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BP11.00134: Controlling Laser Plasma Instabilities Using Temporal Bandwidths Under Shock Ignition Relevant Conditions Frank Tsung, J. Weaver, R. Lehmberg We are performing particle-in-cell simulations using the code OSIRIS to study the effects of laser plasma interactions in the presence of temporal bandwidth under plasma conditions relevant to experiments on the Nike laser with induced spatial incoherence (ISI). With ISI, the instantaneous laser intensity can be 3-4 times larger than the average intensity, leading to the excitation of additional TPD modes and producing electrons with larger angular spread. In our simulations, we observe that although ISI can increase the interaction regions for short bursts of time, time-averaged (over many pico-seconds) laser plasma interactions can be reduced by a factor of 2 in systems with sufficiently large bandwidths (where the inverse bandwidth is comparable with the linear growth time). We will quantify these effects and investigate higher dimensional effects such as laser speckles and the effects of Coulomb collisions. [Preview Abstract] |
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BP11.00135: PIC simulation and experiment comparison on hot electron generation and divergence Eli Borwick, Su-Xing Hu, Chuang Ren, Jun Li We performed PIC simulations using laser and plasma conditions from hydro simulations of an OMEGA experiment (Yakkobi et al. Phys. Plasmas \textbf{20}, 092706 (2013)) where hot electron divergence was measured. The simulations showed few hot electrons were generated under the given hydro conditions, which were just below the thresholds for SRS and TPD. Increasing the electron temperature by 20{\%} increased hot electron generation but increasing the laser intensity did not. A newly developed diagnostic showed significant hot electron divergence when they were present, agreeing with the experiment. The results indicate that 1. the hydro conditions may be different in the experiment and the simulations and 2. hot electron generation may not scale with the TPD threshold parameter. [Preview Abstract] |
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BP11.00136: Modeling Laser-Plasma Interactions in a Magnetized Plasma Eva Los, D. J. Strozzi, T Chapman, W. A. Farmer, B. I. Cohen We consider how laser-plasma interactions, namely stimulated Raman and Brillouin scattering, develop in the presence of a background magnetic field. Externally-launched waves in magnetized plasma have been studied in magnetic fusion devices for several decades, with relatively little work on their parametric decay. The topic has received scant attention in the laser-plasma and high-energy-density fields, but is becoming timely. The MagLIF pulsed-power scheme relies on an imposed axial field and laser-preheat [S. Slutz et al., Phys. Rev. Lett. 2012]. Imposing a field on a hohlraum to reduce hotspot losses has also been proposed [L. J. Perkins et al., Phys. Plasmas 2013]. We consider how the field affects the linear light waves in a plasma, e.g. by decoupling the left- and right- circular polarizations (Faraday rotation). Parametric instability growth rates are presented, as functions of plasma conditions, field strength, and geometry. The scattered-light spectrum, which is routinely measured, is also found. [Preview Abstract] |
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BP11.00137: Characterization of long-scale-length plasmas produced from plastic foam targets for laser plasma instability (LPI) research Jaechul Oh, J. L. Weaver, V. Serlin, S. P. Obenschain We report on an experimental effort to produce plasmas with long scale lengths for the study of parametric instabilities, such as two plasmon decay (TPD) and stimulated Raman scattering (SRS), under conditions relevant to fusion plasma. In the current experiment, plasmas are formed from low density (10-100 mg/cc) CH foam targets irradiated by Nike krypton fluoride laser pulses ($\lambda= 248$ nm, 1 nsec FWHM) with energies up to 1 kJ. This experiment is conducted with two primary diagnostics: the grid image refractometer (Nike-GIR)$^a$ to measure electron density and temperature profiles of the coronas, and time-resolved spectrometers with absolute intensity calibration to examine scattered light features of TPD or SRS. Nike-GIR was recently upgraded with a $5^{th}$ harmonic probe laser ($\lambda= 213$ nm) to access plasma regions near quarter critical density of 248 nm light ($4.5 \times 10^{21}$ cm$^{-3}$). The results will be discussed with data obtained from 120 $\mu$m scale-length$^a$ plasmas created on solid CH targets in previous LPI experiments at Nike. $^a$ J. Oh, et al, Rev. Sci. Instrum. 86, 083051 (2015). [Preview Abstract] |
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BP11.00138: Long Scalelength Plasmas for LPI Studies at the Nike Laser J. L. Weaver, J. Oh, J. W. Bates, A. J. Schmitt, D. M. Kehne, M. F. Wolford, S. P. Obenschain, V. Serlin, R. H. Lehmberg, R. K. Follett, J. G. Shaw, J. F. Myatt, P. W. McKenty, M. S. Wei, H. Reynolds, J. Williams, F. Tsung Studies of laser plasma instabilities (LPI) at the Nike laser have mainly used short pulses, small focal spots, and solid plastic (CH) targets that have yielded maximum gradient scalelengths below 200 microns. The current experimental effort aims to produce larger volume plasmas with 5-10x reduction in the density and velocity gradients as a platform for SBS, SRS, and TPD studies. The next campaign will concentrate on the effects of wavelength shifting and bandwidth changes on CBET in low density (5-10 mg/cm$^{\mathrm{3}})$ CH foam targets. This poster will discuss the development of this new LPI target platform based on modelling with the LPSE code developed at LLE. The presentation will also discuss alternative target schemes (e.g. exploding foils) and improvements to the LPI diagnostic suite and laser operations; for example, a new set of etalons will be available for the next campaign that should double the range of available wavelength shifting. Upgrades to the scattered light spectrometers in general use for LPI studies will also be presented. [Preview Abstract] |
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