Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session TO7: Waves and Basic Computational and Theoretical Methods 
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Chair: Dustin Fisher, University of New Mexico Room: OCC B117119 
Thursday, November 8, 2018 9:30AM  9:42AM 
TO7.00001: Modulation of ion beams by relativistic electron beamplasma instability Zhanghu Hu, Xiaojuan Wang, Yongtao Zhao, Younian Wang Twodimensional (2D) electromagnetic particleincell (PIC) simulations are performed to investigate the transport of relativistic electron beams comoved with a proton beam in collisionless plasmas. For the beam with the radius much larger than plasma skin depth, the current filamentation instability excited by the relativistic electron beam can be clearly observed and the transverse magnetic fields in the plasma increase significantly. The proton beam is modulated strongly by the electromagnetic fields in plasmas and a netlike structure in the beam profile is formed with a high density contrast, which can be provided as an effective tool to diagnose the instability. The dynamic effects of plasma ions are shown to be important and play a significant role on the dynamic evolution of the proton beam. 
Thursday, November 8, 2018 9:42AM  9:54AM 
TO7.00002: Whistler wave propagation and interplay between electron inertia and Larmor radius effects Garima Joshi, G. Ravi The influence of finite Larmor radius effects in the propagation of whistler waves is investigated experimentally in the laboratory plasma. The waves are excited using a loop antenna of diameter less than electron skin depth, the natural scale length in this regime. In an earlier experiment, it was shown that such waves assume an elongated shape with perpendicular dimensions of the order of skin depth. In the present work, we show that the wave propagation is significantly modified when external guiding magnetic field is decreased. The wave spread in the perpendicular direction in spite of starting of as an elongated whistler due to electron inertia effects. In the near region, antenna field becomes dominant even forming null points, however physical processes take shape and wave is still guided. However, the feeble magnetic field in the region away from the antenna is unable to guide the wave any further and wave packet spreads. In spite of large current pulse, the wave remains linear probably because the physical processes are confined within a short distance of skin depth where antenna field dominates. The observed results are attributed to the interplay between electron inertia and finite Larmor radius effects and are explained in terms of a modified physical model. 
Thursday, November 8, 2018 9:54AM  10:06AM 
TO7.00003: Destabilization of Alfvenic fluctuations by a parallelion beam on the Large Plasma Device Gurleen Bal, Shreekrishna Tripathi, Troy Carter An energetic (15KeV at 10 Amps) hydrogen ion beam was axially injected into a magnetized hydrogen plasma with a magnetizing field ranging from 300 to 1500 Gauss. This experiment was conducted on the Large Plasma Device (LAPD) using a barium oxide source. Excitations of shear Alfven waves by energetic ions through resonant processes such as Dopplershifted ioncyclotronresonance (DCIR) and Landau resonance have been observed in the past on the LAPD^{1}. We have observed fluctuations at subcyclotron range of frequencies that cannot be explained by the above resonance processes. We will present results of our preliminary analysis exploring the possibility of these waves being generated by beam associated pressure and momentum gradients. [1] S.K.P. Tripathi, B. Van Compernolle, W. Gekelman, P.Pribyl, and W. Heidbrink, PRL 119, 205002, APS (2016). 
Thursday, November 8, 2018 10:06AM  10:18AM 
TO7.00004: PIC simulations of the damping of nonlinear electron plasma waves propagating in magnetic fields Benjamin J Winjum, Warren B Mori Nonlinear electron plasma waves propagating perpendicular to magnetic fields can be damped due to the fact that trapped electrons get accelerated perpendicularly across the wave front, continually extracting energy from it. We present particleincell simulations of externally driven electron plasma waves showing how the initial damping of the wave, the evolution of the wave after several bounces, and its longtime evolution after many bounce times are all effected by even weak magnetic fields (ω_{c}/ω_{p} << 1). This behavior can have significant consequences for instabilities that are sensitive to the nonlinear evolution of electron plasma waves. We use these results to inform simulations of backward stimulated Raman scattering in which small normalized magnetic fields applied perpendicularly to a light wave increase the instability’s kinetic threshold and decrease the total reflectivity. 
Thursday, November 8, 2018 10:18AM  10:30AM 
TO7.00005: Propagation of EM Signals through a High Speed Flow with Ion Acoustic Wave Instabilities when Signal Frequencies are close to Plasma Frequency of the Flow Saba Mudaliar It is known that in the absence of external magnetic field a high speed flow with velocity shear will lead to ion acoustic wave instabilities. Electromagnetic (EM) signals propagating through the flow will get scattered by the instabilities resulting in shifts in signal wavenumbers and frequencies. When the EM signal frequencies are large compared to the plasma frequency of the flow the scattering process is entirely electromagnetic in nature. However, when the signal frequencies are close to the plasma frequency of the flow, the scattered fields will be partly electrostatic (Langmuir) and partly EM. Multiple scattering will lead to coupling and energy exchange between the electrostatic and EM parts. The coherent part of the scattered waves has the same spectrum as that of the source signal. The diffuse part is obtained as a convolution (in wavenumber and frequency) of the source signal with the spectrum of electron density fluctuations. This is a constrained convolution in the sense that the spectrum has to satisfy the IAW dispersion relation. The mean free path is a key quantity that determines the significance of coherent and diffuse parts. We will highlight details of the impact of the IAW turbulence on radiation and reception of EM signals with the help of examples. 
Thursday, November 8, 2018 10:30AM  10:42AM 
TO7.00006: Considerations in Investigating LaserSolid Interactions through Computer Simulations Asher Davidson, Luke A Johnson, George M Petrov, Daniel Gordon, Joseph Penano We are investigating secondary radiation generation from a short pulse laser incident on a solid surface. Studies involving simulations of related processes already exist in literature, and suggest future potential for computational models that capture these processes in a physically meaningful and computationally efficient manner. A complete understanding of such processes requires consideration of both ParticleinCell (PIC) simulations, to capture the kinetic processes, and fluid dynamic simulations, to capture processes better described by a thermal picture. A recently implemented Quasi3D geometry in the OSIRIS, PIC simulation framework may enable direct calculations of radiation resultant from particle motion. Existing plasma and hydrodynamic simulation frameworks may be modified and extended to facilitate these needs as necessary. The Turbowave plasma simulation framework, currently developed at the U.S. Naval Research Lab (NRL), will be discussed in relation to its current and future development in this context. 
Thursday, November 8, 2018 10:42AM  10:54AM 
TO7.00007: Toroidal Polynomials Isomorphic to Ignition Scattering Functions in Fusion Conditions Stephen Sharma Nuclear fusion is achieved through the selfsustaining chain reaction of particles in various geometries. One of the most interesting and novel structures developing fusion is the tokamak. Solving the Poisson equation and the Lagrangian for geodesics in the toroidal geometry requires the development of a new function called the toroidal elliptic function. As the coordinate system has problems with skewness, the components of the differential equation solution cannot be separated. Thus, the dot product is modified to account for overlapping coordinates. The importance of finding analytic solutions to fusion scattering and geodesic problems has implications in supersymmetry/standard model predictions and practical energy production in the H mode. This work is an effort to create polynomials of infinite order and recursion relations that define coefficients that completely describe a set of eigenfunctions in a toroidal shape. Denoted by a special letter, these toroidal elliptic functions are written in spherical, cylindrical, and Cartesian polynomials to simplify the difficult task of finding an isomorphic analytic and computational model for particles moving along geodesics in a tokamak. 
Thursday, November 8, 2018 10:54AM  11:06AM 
TO7.00008: Distributed Mesh Infrastructure for ParticleinCell Simulations Mark S. Shephard, Eisung Yoon, Seegyoung Seol, Agnieszka Truszkowska, Gopan Perumpilly, Onkar Sahni, William Tobin Particleincell (PIC) methods are an effective tool for fusion plasma simulations. In PIC the particle motion is influenced by the mesh fields and the mesh fields are influenced by particle locations. In applications with complex geometries and varying fields, there is a desire to employ unstructured meshes. Since the operations on the particles dominate computation and memory, particles are always distributed. Although it has been common to maintain a copy of the mesh in each memory space across the parallel computer, the need for higher accuracy for more complex systems is driving a need to also distribute the mesh. This presentation will overview PUMIpic, a distributed unstructured mesh infrastructure to support PIC calculations. PUMIpic employs a distributed mesh with overlap to avoid communication during a push, coordinated gather/scatter, parallel mesh field solve and adjacencybased containment search. The presentation will also discuss the status of two fusion plasma simulation codes being developed using PUMIpic. 
Thursday, November 8, 2018 11:06AM  11:18AM 
TO7.00009: Application of Variational Mechanics to the ChildLangmuir Law Adam Darr, Allen L Garner The ChildLangmuir law yields the space charge limited current density for a onedimensional, planar vacuum gap for a single charged species with no initial velocity with nonrelativistic mechanics under the electrostatic condition and yields a critical current density J_{c} ~ V^{3/2}/D^{2}, where V is the applied voltage and D is the gap distance. This theory may be derived from Poisson’s equation, a capacitance model, or a transit time model (P. Zhang, A. Valfells, L.K. Ang, J. W. Luginsland, and Y. Y. Lau, Appl. Phys. Rev. 4, 011304 (2017)). The transit time model may also be used to derive the LangmuirBlodgett law, which gives J_{c} ~ E_{c}^{3/2}/D^{1/2}, where E_{c} is the vacuum electric field on the cathode. One may also derive scaling laws with cathode protrusions to predict an equivalent multiple dimension ChildLangmuir law. Here, we propose the application of variational mechanics to predict spacecharge limited current in a manner that is independent of reference frame, and thus applicable to planar, cylindrical, and spherical coordinate systems in 1D, 2D, and 3D geometries. The implications and extension of this technique to other spacecharge dominated mechanisms, such as MottGurney for collisions and crossedfield incorporating magnetic field, will be discussed. 
Thursday, November 8, 2018 11:18AM  11:30AM 
TO7.00010: HighOrder Solver for Direct Numerical Simulations of Plasma Flows with Realistic Transport Phenomena Zhaorui Li, Daniel Livescu The twofluid plasma equations with full transport terms, including temperature and magnetic field dependent ion and electron viscous stresses and heat fluxes, frictional drag force, and ohmic heating term have been implemented in the petascale CFDNS code and solved by using the sixthorder nondissipative compact finite differences for plasma flows in several different regimes. In order to be able to fully resolve all the dynamically relevant time and length scales while maintaining computational feasibility, the assumptions of infinite speed of light and negligible electron inertia have been made. The accuracy and robustness of this twofluid plasma solver in handling plasma flows in different regimes have been validated against a series of canonical problems, such as AlfvenWhistler dispersion relation, electromagnetic plasma shock, magnetic reconnection, etc. For all test cases, grid convergence studies have been conducted to achieve fully resolved DNSlike solutions. In addition, the roles of viscosity, heat flux, resistivity and Hall effects are investigated for the canonical flows studied. 
Thursday, November 8, 2018 11:30AM  11:42AM 
TO7.00011: SLPIC: a PIC algorithm for accelerating lowvelocity plasma kinetics modeling Andrew Chap, Thomas G Jenkins, Gregory R Werner, John Robert Cary, Peter Stoltz Speedlimited particleincell simulation (SLPIC) is a PICbased simulation method that allows increased timesteps by slowing down the fastest particles in such a way that slow dynamics of interest are preserved, while significantly reducing the number of timesteps required to complete such a simulation. In a 1D plasma sheath simulation to steadystate, SLPIC demonstrated a speedup advantage over comparable PIC simulation by a factor of 27 for a hydrogen plasma and over 200 for an argon plasma, each time correctly determining the end state of the plasma. SLPIC introduces a speedlimiting factor β(v) ≤ 1, modifying the equations of motion such that dx/dt = β(v)v and dv/dt = β(v)a, and weights particles to the grid as β(v)w where w is the macroparticle weight. SLPIC is accurate as long as β(v_{s}) ≈ 1, where v_{s} (the “speedlimit”) is the maximum velocity of any dynamics of interest, and β(v)v ≤ v_{s}. For the aforementioned sheath simulation, v_{s}_{ }is the ion drift velocity, and the speedup is correlated to the relation ∆t_{SLPIC} = ∆x/v_{s}_{ }≫ ∆t_{PIC }= ∆x/v_{e}_{ }where v_{e} is the maximum electron velocity. The SLPIC speedup relative to PIC arises as we effectively reduce the vast speed differences between electrons and ions. 
Thursday, November 8, 2018 11:42AM  11:54AM 
TO7.00012: Analytic expressions for electronion temperature equilibration rates from the LenardBalescu equation Christian R Scullard, Susana Serna, Lorin Benedict, Charles L Ellison, Frank R Graziani In hydrodynamic plasma simulations, it is necessary to have accurate but easilycomputable formulas for various properties of the plasma. I present here a method for evaluating the electronion equilibration time arising from the LenardBalescu equation, which is accurate in weak coupling. The integrals are too difficult to compute directly within a hydrodynamic simulation, but I will describe the various mathematical techniques we used to derive a simple but accurate formula that holds for arbitrary electron degeneracy. 
Thursday, November 8, 2018 11:54AM  12:06PM 
TO7.00013: Classification and new solutions of the Vlasov equation by means of singularity analysis Piotr P. Goldstein Singularity analysis, which is an extension of the classical Painlev\'e (P) test, is applied to classify solutions of the onedimensional onecomponent VlasovPoisson system and to find its new explicit solutions. As the classical test has been derived for purely differential equations, farreaching modifications are introduced. 
Thursday, November 8, 2018 12:06PM  12:18PM 
TO7.00014: A New Unified Understanding Of Electron And Ion Normal Modes In A1D Electrostatic VlasovPoisson Plasma Pallavi Trivedi, Rajaraman Ganesh Understanding the dynamics of a collisionless plasma is a subject of extensive effort, for both In the present work, using a VlasovPoisson solver, considering both kinetic electrons and kinetic ions on the same physics footing, we demonstrate that the hitherto separate 
(Author Not Attending)

TO7.00015: Dynamics of the Meissner effect: how superconductors expel magnetic fields respecting Alfven's theorem J. E. Hirsch In a perfectly conducting fluid, magnetic field lines move with the fluid (Alfven's theorem). Thus it is natural to expect that the expulsion of magnetic field from the interior of a metal becoming superconducting is associated with expulsion of charge. Surprisingly, this is not part of the conventional understanding of the Meissner effect. We propose a dynamical description of the Meissner effect involving radial outflow of superfluid and backflow of normal fluid in the transition process, that respects Alfven's theorem. The azimuthal Meissner current results from the magnetic Lorentz force acting on the outflowing charge; the backflowing charge transfers its azimuthal momentum to the body as a whole. The driving force for radial outflow is quantum kinetic energy lowering, hence the Meissner effect would not occur in a classical plasma. To satisfy momentum conservation and reversibility it is indispensable that the normal state charge carriers have holelike character [1]. This physics is described by the alternative theory of hole superconductivity [2] and not by the conventional BardeenCooperSchrieffer (BCS) theory. [1] J. E. Hirsch, Annals of Physics 373, 230 (2016); Phys. Rev. B 95, 014503 (2017). [2] References in https://jorge.physics.ucsd.edu/hole.html. 
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