Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session YI3: Complex and Turbulent PlasmasInvited

Hide Abstracts 
Chair: Guru Ganguli, Naval Research Laboratory Room: 210 ABEF 
Friday, November 4, 2016 9:30AM  10:00AM 
YI3.00001: A methodology for the rigorous verification of plasma simulation codes Invited Speaker: Fabio Riva The methodology used to assess the reliability of numerical simulation codes constitutes the Verification and Validation (V\&V) procedure. V\&V is composed by two separate tasks: the verification, which is a mathematical issue targeted to assess that the physical model is correctly solved, and the validation, which determines the consistency of the code results, and therefore of the physical model, with experimental data. In the present talk we focus our attention on the verification, which in turn is composed by the code verification, targeted to assess that a physical model is correctly implemented in a simulation code, and the solution verification, that quantifies the numerical error affecting a simulation. Bridging the gap between plasma physics and other scientific domains, we introduced for the first time in our domain a rigorous methodology for the code verification, based on the method of manufactured solutions, as well as a solution verification based on the Richardson extrapolation [Riva \emph{et al.}, Phys. Plasmas \textbf{21}, 062301 (2014)]. This methodology was applied to GBS [Ricci \emph{et al.}, Plasma Phys. Controlled Fusion \textbf{54}, 124047 (2012), Halpern \emph{et al.}, J. Comp. Phys. \textbf{315}, 388 (2016)], a threedimensional fluid code based on a finite difference scheme, used to investigate the plasma turbulence in basic plasma physics experiments and in the tokamak scrapeoff layer. Overcoming the difficulty of dealing with a numerical method intrinsically affected by statistical noise, we have now generalized the rigorous verification methodology to simulation codes based on the particleincell algorithm, which are employed to solve Vlasov equation in the investigation of a number of plasma physics phenomena. [Preview Abstract] 
Friday, November 4, 2016 10:00AM  10:30AM 
YI3.00002: PlasmaWall Interaction with Strong Electron Emission Revisited Invited Speaker: Michael Campanell Half a century ago, Hobbs and Wesson derived a solution for the plasma sheath at a planar surface with emission coefficient $\gamma $ [1]. They predicted that the floating sheath potential remains negative when $\gamma $ \textgreater 1. Variations of their ``spacecharge limited'' (SCL) sheath model have long been used to estimate the particle and energy fluxes at strongly emitting surfaces [2]. Recent theory, simulation and experimental studies show that another plasmawall equilibrium is possible when $\gamma $ \textgreater 1. In the ``inverse regime'' [3], the sheath potential is positive, repelling ions from the wall. The quasineutral density gradient and force balance in the ``inverted presheath'' are much different from the Bohm presheaths contained in the SCL models. It turns out that a SCL plasmawall equilibrium is only stable under the assumption of zero ionization inside the sheath. Otherwise, the cumulative trapping of new ions in the SCL's potential ``dip'' will force a transition to the inverse regime [4]. It follows that only an inverse equilibrium should be possible in practice at floating surfaces with strong secondary, thermionic or photoelectron emissions. Applications will be discussed. [1] G. D. Hobbs and J. A. Wesson, Plasma Phys. \textbf{9}, 85 (1967) [2] (review) S. Robertson, Plasma Phys. Control. Fusion \textbf{55}, 093001 (2013) [3] M. D. Campanell, Phys. Plasmas \textbf{22}, 040702 (2015) [4] M. D. Campanell and M. V. Umansky, Phys. Rev. Lett. \textbf{116}, 085003 (2016) [Preview Abstract] 
Friday, November 4, 2016 10:30AM  11:00AM 
YI3.00003: Extended MHD Modeling of TearingDriven Magnetic Relaxation Invited Speaker: Joshua Sauppe Driven plasma pinch configurations are characterized by the gradual accumulation and episodic release of free energy in discrete relaxation events. The hallmark of this relaxation in a reversedfield pinch (RFP) plasma is flattening of the parallel current density profile effected by a fluctuationinduced dynamo emf in Ohm's law. Nonlinear twofluid modeling of macroscopic RFP dynamics has shown appreciable coupling of magnetic relaxation and the evolution of plasma flow. Accurate modeling of RFP dynamics requires the Hall effect in Ohm's law as well as first order ion finite Larmor radius (FLR) effects, represented by the Braginskii ion gyroviscous stress tensor. New results find that the Hall dynamo effect from $<\mathbf{J} \times \mathbf{B}>/ne$ can counter the MHD effect from $<\mathbf{V} \times \mathbf{B}>$ in some of the relaxation events. The MHD effect dominates these events and relaxes the current profile toward the Taylor state, but the opposition of the two dynamos generates plasma flow in the direction of equilibrium current density, consistent with experimental measurements. Detailed experimental measurements of the MHD and Hall emf terms are compared to these extended MHD predictions. Tracking the evolution of magnetic energy, helicity, and hybrid helicity during relaxation identifies the most important contributions in singlefluid and twofluid models. Magnetic helicity is well conserved relative to the magnetic energy during relaxation. The hybrid helicity is dominated by magnetic helicity in realistic lowbeta pinch conditions and is also well conserved. Differences of less than $1\%$ between magnetic helicity and hybrid helicity are observed with twofluid modeling and result from cross helicity evolution through ion FLR effects, which have not been included in contemporary relaxation theories. The kinetic energy driven by relaxation in the computations is dominated by velocity components perpendicular to the magnetic field, an effect that had not been predicted. [Preview Abstract] 
Friday, November 4, 2016 11:00AM  11:30AM 
YI3.00004: Explosive attractor solutions to a universal cubic delay equation Invited Speaker: David SanzOrozco This presentation describes new explosive attractor solutions to the universal cubic delay equation found in both the fluid [F. J. Hickernell, Jour. Fluid Mechanics, 142, 431 (1984)] and (for a kinetic system) in the plasma literature [B. N. Breizman et al. Phys. Plas. 4, 1559 (1997)]. Our results will be explained in the notation of the plasma problem, where a cubic delay equation describes the evolution of a wave in a kinetic system, and is characterized by a control parameter $\phi$ (its value is determined by the linear properties of the kinetic response). The linear eigenvalues do not exist in absence of the kinetic response (with exceptions for $\phi=0$ or $\pi$) but with the kinetic contribution, marginally unstable modes emerge when the kinetic drive is at a critical level. The simulation of the temporal evolution reveals the development of an explosive mode, i.e. a mode growing without bound in a finite time. The two main features of the response are: (1) a wellknown explosive envelope $(t_0t)^{5/2}$, with $t_0$ the blowup time of the amplitude; (2) a spectrum with everincreasing oscillation frequencies that is criticallydependent upon the parameter $\phi$. A code has been constructed that resolves these oscillations over many periods by calculating their Fourier transform with respect to the pseudotime $x=\ln(t_0t)$. In addition, our analytic modeling explains the results and quantitatively nearly replicates the attractor solutions found in the simulations. A physical result of these solutions is the development of frequency chirping of the observed wave. This effect continues beyond the applicability of the cubic delay equation [H. L. Berk et al., Phys. Plas. 6, 3102 (1999)], and thus the attractor solutions that we study represent precursors to longlived phenomena that may be used in an experimental situation to understand the nature of a system's equilibrium. [Preview Abstract] 
Friday, November 4, 2016 11:30AM  12:00PM 
YI3.00005: Extending geometrical optics: A Lagrangian theory for vector waves Invited Speaker: D. E. Ruiz Even diffraction aside, the commonly known equations of geometrical optics (GO) are not entirely accurate. GO considers wave rays as classical particles, which are completely described by their coordinates and momenta, but rays have another degree of freedom, namely, polarization. As a result, wave rays can behave as particles with spin. A wellknown example of polarization dynamics is wavemode conversion, which can be interpreted as rotation of the (classical) ``wave spin.'' However, there are other lessknown manifestations of the wave spin, such as polarization precession and polarizationdriven bending of ray trajectories. This talk presents recent advances in extending and reformulating GO as a firstprinciple Lagrangian theory, whose effectivegauge Hamiltonian governs both mentioned polarization phenomena simultaneously. Examples and numerical results are presented. When applied to classical waves, the theory correctly predicts the polarizationdriven divergence of left and right polarized electromagnetic waves in isotropic media, such as dielectrics and nonmagnetized plasmas. In the case of particles with spin, the formalism also yields a pointparticle Lagrangian model for the Dirac electron, i.e. the relativistic spin1/2 electron, which includes both the SternGerlach spin potential and the BargmannMichelTelegdi spin precession. Additionally, the same theory contributes, perhaps unexpectedly, to the understanding of ponderomotive effects in both wave and particle dynamics; e.g., the formalism allows to obtain the ponderomotive Hamiltonian for a Dirac electron interacting with an arbitrarily large electromagnetic laser field with spin effects included. [Preview Abstract] 
Friday, November 4, 2016 12:00PM  12:30PM 
YI3.00006: Transport Bifurcation in Plasma Interchange Turbulence Invited Speaker: Bo Li Transport bifurcation and mean shear flow generation in plasma interchange turbulence are explored with selfconsistent twofluid simulations in a fluxdriven system with both closed and open field line regions. The nonlinear evolution of interchange modes shows the presence of two confinement regimes characterized by the low and high mean flow shear. By increasing the input heat flux above a certain threshold, largeamplitude oscillations in the turbulent and mean flow energy are induced. Both clockwise and counterclockwise types of oscillations are found before the transition to the second regime. The fluctuation energy is decisively transferred to the mean flows by largeamplitude Reynolds power as turbulent intensity increases. Consequently, a transition to the second regime occurs, in which strong mean shear flows are generated in the plasma edge. The peak of the spectrum shifts to higher wavenumbers as the largescale turbulent eddies are suppressed by the mean shear flow. The transition back to the first regime is then triggered by decreasing the input heat flux to a level much lower than the threshold for the forward transition, showing strong hysteresis. During the back transition, the mean flow decreases as the energy transfer process is reversed. This transport bifurcation, based on a fieldlineaveraged 2D model, has also been reproduced in our recent 3D simulations of resistive interchange turbulence, in which the ion and electron temperatures are separated and the parallel current is involved. [Preview Abstract] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2022 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700