Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Plasma Physics
Volume 56, Number 16
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session GP9: Poster Session III: Fundamental Theory and Modeling I; ITER and Magnetic Fusion Development; Plasma Confinement Configurations & Stellerator; ICF and HED Plasmas, Simulations, Hydrodynamic Instability |
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Room: Hall A |
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GP9.00001: FUNDAMENTAL THEORY AND MODELING I |
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GP9.00002: Asymptotic-preserving Lagrangian approach for modeling anisotropic transport in magnetized plasmas Luis Chacon, Diego del-Castillo-Negrete Modeling electron transport in magnetized plasmas is extremely challenging due to the extreme anisotropy introduced by the presence of the magnetic field ($\chi_{\parallel}/\chi_{\perp} \sim 10^{10}$ in fusion plasmas). Recently, a novel Lagrangian method has been proposed\footnote{D. del-Castillo-Negrete, L. Chac\'on, \emph{PRL}, {\bf 106}, 195004 (2011); DPP11 invited talk by del-Castillo-Negrete} to solve the local and non-local \emph{purely} parallel transport equation in general 3D magnetic fields. The approach avoids numerical pollution (in fact, it respects transport barriers --flux surfaces-- exactly by construction), is inherently positivity-preserving, and is scalable algorithmically (i.e., work per degree-of-freedom is grid-independent). In this poster, we discuss the extension of the Lagrangian approach to include perpendicular transport and sources. We present an asymptotic-preserving numerical formulation that ensures a consistent numerical discretization temporally and spatially for {\em arbitrary} $\chi_{\parallel}/\chi_{\perp}$ ratios. This is of importance because parallel and perpendicular transport terms in the transport equation may become comparable in regions of the plasma (e.g., at incipient islands), while remaining disparate elsewhere. We will demonstrate the potential of the approach with various challenging configurations, including the case of transport across a magnetic island in cylindrical geometry. [Preview Abstract] |
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GP9.00003: Efficient Hybrid Methods for the Simulation of Plasmas with Coulomb Collisions M.S. Rosin, R.E. Caflisch, A.M. Dimits, B.I. Cohen Hybrid algorithms can achieve high efficiency for the kinetic simulation of plasmas with Coulomb collisions at moderately small Knudsen number by combining a fluid solver to evolve the mostly dominant Maxwellian part of the distribution function, and particle-in-cell and Monte-Carlo collision implementations to evolve the non-Maxwellian part of the distribution function. Various choices are possible. Binary or Langevin-equation-based Monte-Carlo collisions may be used. The kinetic component may be treated using a ``full'' (fixed-weight) or delta-f (variable-weight) particle-in-cell (PIC) method. The implementation of physical conservation laws may involve either shifting and rescaling the particle velocities or changes to the particle weights (``delta-f'' sources). This presentation will examine the performance of hybrid simulation schemes and the relative benefits of these various options on relevant kinetic test problems including isotropization, heating, injection, sheath and transport problems. [Preview Abstract] |
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GP9.00004: Higher-order Time Integration of Coulomb Collisions in a Plasma Using Langevin Equations A.M. Dimits, B.I. Cohen, R.E. Caflisch, M.S. Rosin We examine the extension of Langevin-equation Monte-Carlo algorithms for Coulomb collisions from the conventional Euler $O$(\textit{$\Delta $t}$^{1/2})$-order time integration to the next higher [Milstein-$O$(\textit{$\Delta $t})] order. In one common Langevin-equation approach, the angular scattering step is treated with a combination of near-Cartesian stochastic velocity-direction kicks, in a unit-vector frame that is rotated so that at the beginning of each timestep, one axis is aligned with the velocity direction. We find that in such schemes, the angular component of the collisional scattering cannot be extended beyond the Euler order. Instead, the extension to higher order proceeds through a formulation of the angular scattering directly as stochastic differential equations in the two fixed-frame spherical coordinates. Such an algorithm involves generation of random numbers that sample the joint distribution function of both the (Gaussian) random coordinate displacements and of double stochastic ``area integrals.'' The sampling of the area integrals can be made using simple but highly accurate approximations to results on ``Levy-area'' processes. Implications for particle simulation of Coulomb collisions in plasmas are discussed. [Preview Abstract] |
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GP9.00005: Particle Acceleration and Energy Conservation in Particle In Cell Simulations Giovanni Lapenta, Stefano Markidis Particle acceleration is a process of great importance in all areas of plasma physics. In most cases, kinetic effects are dominant and require a full kinetic treatment, such as the Particle in Cell (PIC) method. PIC methods are widely used in all aspects of plasma physics, proving to be a precious and irreplaceable tool. Yet all methods in use and published conserve energy to a good approximation, but not exactly. A well known property of PIC methods, documented extensively in all textbooks, is that energy is not conserved exactly. In fact the particle noise is a unphysical source of energy that, when insufficient resolution is used, can make the simulations go unstable. In the present paper we apply a new exactly energy conserving scheme and demonstrate that indeed exact energy conservation plays a key role in determining the correct spectrum of the accelerated particles. [Preview Abstract] |
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GP9.00006: An implicit-moment Coulomb collision algorithm for particle-in-cell simulations David Larson, Tanim Islam Particle pairing algorithms are the standard tool for including the effects of Coulomb collisions in PIC plasma simulation codes. These algorithms are restricted to resolving the characteristic collision frequency in order to maintain accuracy. We introduce a new algorithm using recent work by Fox and co-workers [1-3] to generate a discrete set of quadrature nodes representing the velocity distribution. These nodes are advanced in time using the collisional drag force. The original set of PIC particles then collides with the time-advanced nodes using the Nanbu collision algorithm [4]. The result is an implicit-moment collision algorithm that works well for large time steps as demonstrated in a variety of test problems.\\[4pt] [1] R.O. Fox, J. Comp. Phys. \textbf{227} (2008)\\[0pt] [2] O. Desjardins et al., J. Comp. Phys.\textbf{227} (2008)\\[0pt] [3] C. Yuan and R.O. Fox, ``Conditional quadrature method of moments for kinetic equations,'' J. Comp. Phys. (in review)\\[0pt] [4] K. Nanbu and S. Yonemura, J. Comp. Phys. \textbf{145 }(1998) [Preview Abstract] |
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GP9.00007: Low-noise, energy-conserving implicit PIC D.C. Barnes, L. Chac\'on, G. Chen The IMP method solves the collisionless Vlasov equation with an evolving background \textit{$\delta $f} method which has a discrete exactly conserved energy. Obvious advantages are lack of several common PIC and \textit{$\delta $f} diseases, such as aliasing instability and secular weight growth. We review previous demonstrations of the method for wave damping and two-stream instability. We present new two-dimensional, fully electromagnetic, fully nonlinear simulations of the g-mode. We also present the formulation of the problem with significant background temperature gradient, and show how to avoid growing weights by allowing mixing of the background to provide the required entropy increase. Initial results for the case of background temperature gradient are presented and show energy conservation and bounded weights.. [Preview Abstract] |
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GP9.00008: A Comparison of Fully Implicit and Semi Implicit Time Integration Methods for a 3T Plasma Matthew Calef, John Wohlbier A common model for dense plasmas represents the radiation, electron and ion energy densities as coupled diffusive quantities. Within this ``3T'' model the diffusion and coupling coefficients depend on underlying state data yielding non-linear PDEs. One method for integrating these PDEs in time is, at each time step, to use coupling and diffusion coefficients from the previous time step. Further, one may split the time step into smaller sub-steps where each process is advanced independently. While this semi-implicit ``operator-split'' and ``lagged'' approach greatly simplifies the numerical problem, the solution is less accurate than the solution obtained from solving the fully implicit coupled system. In this work we present a fully implicit method for integrating in time a coupled ``3T'' model. Our method employs a geometric multigrid solver with line relaxation for solving the constituent elliptic problems, a preconditioner based on corrected operator-splitting and a Krylov acceleration for converging the nonlinear residual at each update. We compare the result of this method with the results from an operator-split lagged integration method for a ``hot spot'' problem motivated by a NIF implosion. This problem includes stiff non-linearities and jump discontinuities in diffusion coefficients. [Preview Abstract] |
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GP9.00009: Particle-in-Cell Simulation of Plasma Blob Dynamics Hiroki Hasegawa, Seiji Ishiguro Recently, it has been reported that long-lived coherent structures ``blobs'' in scrape-off layer (SOL) of magnetic confinement fusion devices propagate from the edge of core plasma to the first wall. Blobs are thought to transport a plasma into the far (second) SOL across magnetic field lines. Many theoretical and numerical works based on two-dimensional reduced fluid models have been performed and dynamics of blobs have been investigated. However, in this kind of macroscopic model, kinetic effects, such as sheath formation between plasma and divertor plate, are treated under some assumptions and parameterization. In this study, for the purpose of investigating blob dynamics including such kinetic effects, we have developed a three dimensional electrostatic particle-in- cell simulation code with particle absorbing boundaries. Results of preliminary simulations show that blobs move to the first wall across the magnetic field lines and the relation between the observed propagation speed of the blob and the initial effective width of the blob in the poloidal direction is consistent with the fluid theory. [Preview Abstract] |
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GP9.00010: QPIC: A Many-Fermion Quantum PIC Code Chris Fichtl, Michael Murillo, Frank Graziani We are developing a 3d-3v many-fermion quantum PIC code capable of simulating conditions in which the plasma electrons are weakly coupled and moderately degenerate, such that the quantum Vlasov (Wigner) equation appropriately describes their phase space dynamics according to an initial Wigner distribution. Since PIC relies on a grid to obtain the field equations, the quantum mechanical smearing term cannot be accurately resolved; the quantum Vlasov treatment then becomes numerically equivalent to the classical Vlasov treatment for an initial quantum distribution, chosen to be Fermi-Dirac. This allows us to use standard PIC techniques as a starting point. PIC codes are known to suffer from numerical errors which can cause relaxation of non-Maxwellian initial conditions over long simulation times. We have therefore developed a Langevin velocity-scaling approach designed to help mitigate these errors. Our approach, its associated implementation, and preliminary physics benchmarking results, such as nonlinear plasma waves and instabilities at various degeneracies, will be presented. Finally, methods for extending QPIC's current capability will be outlined. [Preview Abstract] |
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GP9.00011: Fully kinetic 3D electromagnetic particle-in-cell model of streamer formation and dynamics in high-pressure electronegative gases D.V. Rose, D.R. Welch, N. Bruner, R.E. Clark, T.C. Genoni, C. Thoma, W.R. Zimmerman, P.K. Rambo, B.W. Atherton Streamer and leader formation in high pressure devices is a dynamic process involving a hierarchy of physical phenomena. These include elastic and inelastic particle collisions in the gas, radiation generation, transport and absorption, and electrode interactions. We present a new 3D fully EM implicit particle-in-cell simulation model of gas breakdown leading to streamer formation in electronegative gases. The model uses a Monte Carlo treatment for all particle interactions and includes discrete photon generation, transport, and absorption for ultra-violet and soft x-ray radiation. Central to the realization of this fully kinetic particle treatment is an algorithm [D. R. Welch, et al., J. Comp. Phys. 227, 143 (2007)] that manages the total particle count by species while preserving the local momentum distribution functions and conserving charge. [Preview Abstract] |
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GP9.00012: Numerical method for kinetic dense plasma transport Mark L. Adams The development of novel theoretical and computational kinetic models is required to describe the nonlocal and non-Markovian transport channels that exist in a growing number of high energy density physics (HEDP) laboratory experiments. In this poster I develop a numerical method that significantly accelerates the convergence of computational kinetic transport methods in dense plasmas. The method self- consistently couples a kinetic transport model with a set of moment equations that conserve mass, momentum, and energy as well as retain the salient properties of the Boltzmann H-theorem. Extensions of the method to multi-component plasmas and dynamic boundary conditions are considered. I illustrate the method using common parallel plate, shock, and plasma relaxation problems; the examples show rapid convergence in the collisional limit and retain the appealing properties of the kinetic transport computational method in the collisionless limit. The numerical method it is easily extensible to more sophisticated kinetic transport models, computational methods, and higher dimensions. [Preview Abstract] |
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GP9.00013: The Linear Stability of the ITG Mode using the NIMROD Code Dalton Schnack, Ping Zhu, Carl Sovinec, Chris Hegna We demonstrate that the linear instability of the Ion Temperature Gradient (ITG) mode can be computed with the extended MHD code NIMROD. The ITG is related to a parallel sound wave that is destabilized by two-fluid and FLR effects in the presence of an ion temperature gradient. It can be unstable in configurations that are otherwise ideal and resistive MHD stable. We show analytically that the ITG can be described in slab geometry using both two-fluid (separate electron and ion equations) and the equivalent single fluid (center of mass) form that is solved in NIMROD. These analytic calculations use the local approximation and the ballooning ordering. They include the Braginskii ion gyro-viscous stress tensor that encapsulates the lowest order ion FLR effects. Linear two fluid/FLR numerical calculations with the NIMROD code, which does not employ either the local approximation or the ballooning ordering, are in reasonable agreement with the predicted growth rates and marginal points. Therefore, the extended MHD model used in NIMROD is capable of capturing the effects of this instability within the context of global fluid simulations. [Preview Abstract] |
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GP9.00014: Computational Co-Design of a Scale-bridging Plasma Simulation Algorithm for Emerging Architectures D.A. Knoll, W.S. Daughton, B. Srinivasan, C.N. Newman, W.T. Taitano Los Alamos National Laboratory has recently initiated a new project on the topic of Computational Co-design of Multi-scale Algorithms in the Natural Sciences (CoCoMANS). We define computational co-design and the synergistic interaction of Application, Algorithms and Architectures to produce a new class of physics simulation capability. One of our focus application areas will be plasma physics, and one of the goals of the project will be to demonstrate a paradigm shift in plasma kinetic simulation on emerging, heterogeneous computer architectures. We are developing moment-based scale-bridging algorithms with the goal of enabling system scale simulation with self-consistent kinetic effects. These algorithms will be optimized with emerging heterogeneous computer architectures as the target computing platform. In this poster we discuss our computational co-design process, describe the aspects of the moment-based scale-bridging algorithms and the required solver for the stiff moment system. We will provide some algorithmic proof-of-principle, and we will demonstrate the implementation of the general scale-bridging algorithm on a heterogeneous architecture. [Preview Abstract] |
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GP9.00015: Fully Implicit Moment-Based Acceleration of Vlasov-Ampere Particle in Cell (PIC) System William Taitano, Dana Knoll, Luis Chacon Explicit time integration is predominant in particle-in-cell (PIC) method. In explicit method, the time-step size is restricted by the CFL condition. This makes detailed investigation of such problems that occurs in ion time-scale challenging. Implicit method is not restricted by any of the numerical time-scales. Jacobian-Free-Newton-Krylov (JFNK) is one method that solves a coupled set of non-linear system of equations that promises investigation of implicit multi-time-scale kinetic plasma physics simulation possible [1]. With appropriate discretization, one can also use a mesh spacing which is larger than the Debye length. An alternative implicit approach have also been investigated by Degond et al [2]. The approach is formulated around a semi-implicit, reformulated Poisson's equation in order to remove the stiffness associated with the pure Poisson equation to solve for the electric-field. Our work is based on developing a moment-based approach which may allow us to abandon the tight JFNK iteration between fields and particles. We present our progress on this new multi-scale algorithm and contrast it with the approaches of [1] and [2]. We will also show a connection to moment-based acceleration of transport iteration used to solve for the neutron transport equation.\\[4pt] [1] G. Chen, et al., J. Comp. Phys. in press.\\[0pt] [2] P. Degond, et al., J. Comp. Phys. [Preview Abstract] |
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GP9.00016: Two-Fluid Plasma Lattice Boltzmann Model Jens von der Linden, Setthivoine You A two-fluid plasma model based on lattice Boltzmann (LB) methods [1] is developed and extended to include neutrals, free vacuum boundaries and embedded solid targets. LB methods model fluids by evolving distribution functions of a discretized Boltzmann-BGK equation over a limited set of velocities. The continuum equations can be recovered with a Chapmann-Enskog expansion. Similarly the electromagnetic fields are evolved as distribution functions with moments and equilibria chosen such that multi- scale expansions retrieve Maxwell's equations. The Lorentz force couples the plasma and electromagnetic lattices. Neutrals are added with a conventional LB fluid which interacts through source and sink terms at the lattice nodes. Free vacuum boundaries are modeled with modified collisional operators to allow for free streaming in low density regions. The novel numerical tool will support experimental interpretation of a new generalized plasma relaxation experiment and a study on the innovative use of plasma jets for deflection of space targets.\\[4pt] [1] M. Mendoza \& J. D. Munoz. (2008) Three-dimensional lattice Boltzmann model for magnetic reconnection. Phys. Rev. E 77, 026713 [Preview Abstract] |
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GP9.00017: Efficient GPU implementation for implicit particle-in-cell simulations G. Chen, L. Chac\'on, D.C. Barnes A recent proof-of-principle study of an energy- and charge-conserving, fully implicit particle-in-cell (PIC) algorithm\footnote{G. Chen, L. Chac\'on, and D.C. Barnes, {\it J. Comput. Phys.} {\bf 18}(2011).} demonstrated that accurate and efficient PIC simulations with very large time steps are possible. A key component of the algorithm is the enslavement of particle orbits to the field equations. With particle enslavement, orbit integration is a segregated operation, which is perfectly suited for emerging heterogeneous architectures that combine CPUs with GPUs. The use of GPUs is promising on implicit PIC, as it is naturally data parallel (thus suited for extreme multi-threading), and it is compute-bounded (vs. explicit schemes, typically memory-bounded). However, the particle mover in [1] is adaptive, and particles have to stop at cell-boundaries to conserve charge locally. This creates load imbalances and dynamic control flows, which poses a challenge to utilize fully the GPU computing power. This work demonstrates that a highly efficient GPU implementation of the implicit particle mover (using CUDA) is possible. We obtain 300 to 400 GOps/s (counting floating, integer and special function operations) using single precision. This is about 20\% to 25\% of the peak performance of the GPU (GeForce GTX580), and about 200 to 300 times faster than a single CPU (Xeon@3.16GHz) implementation. [Preview Abstract] |
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GP9.00018: Geometric Phase of the Gyromotion in Adiabatic Magnetic Field Jian Liu, Hong Qin In magnetic field changing slowly with time and/or space, the gyromotion of charged particles is quasi-periodic. When describing it by gyrocenter coordinate, the gyrophase turns out to have an additional part, called geometric gyrophase, besides the normal dynamical phase. It is an example of the geometric phase which has many important applications in different branches of physics. Its name comes from elegant geometric meaning and deep geometric origin, the noncommutativity of rotation operations. Its value depends only on the evolving path in a parameter space. If the magnetic field returns to its initial value after a loop in the parameter space, the value is equal to the solid angle spanned by the loop. Compared with the Berry phase of electron's spin wave function in the same adiabatic field, the similarities and distinctions reveal the similar geometric nature in different physical laws. The study on geometric gyrophase clarifies that we cannot avoid problems such as the definition of gyrophase and the gauge choice for local frames, when applying the gyrokinetics in varying magnetic fields. [Preview Abstract] |
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GP9.00019: A discontinuous Galerkin method for Vlasov - like systems I.M. Gamba, Yingda Cheng, P.J. Morrison The discontinuous Galerkin (DG) method developed by some of us for integrating the Vlasov-Poisson system\footnote{R.E.~Heath, I.M.\ Gamba, P.J.\ Morrison, and C.\ Michler, arXiv:1009.3046v1 [physics.plasm-ph].} is described and generalized. Higher order polynomials on basis elements are used and extensive error analyses, including recurrence properties, are discussed. The method is conservative and preserves positivity of the distribution function. Several linear and nonlinear examples are treated that elucidate the DG methods ability to resolve filamentation and obtain high resolution BGK states. [Preview Abstract] |
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GP9.00020: A General Theory for Gauge-Free Lifting P.J. Morrison Given a Hamiltonian set of orbit equations, defined on a phase space of arbitrary dimension, with `forces' that depend explicitly on given electric and magentic fields and possibly all of their derivatives, how does one \underline{lift} to a Hamiltonian kinetic theory coupled to Maxwell's equations? A general theory that answers this question will be presented. The theory produces magnetization and polarization effects in Maxwell's equations via a Poisson bracket that generalizes that for the Vlasov-Maxwell system.\footnote{P.J.~Morrison, Phys.Lett.\ {\bf 80A}, 383 (1980); AIP Conference Proceedings {\bf 88}, 13 (1982).} Several examples will be treated, including the generalized guiding-center kinetic theory of Pfirsch and the author,\footnote{D.~Pfirsch and P.J.~Morrison, Phys.\ Rev.\ \textbf{32A}, 1714 (1985); Phys.\ Fluids \textbf{3B}, 271 (1991).} which relies on the introduction of redundant variables via Dirac constraint theory, and a theory that incorporates spin in the Vlasov context.\footnote{M.~Marklund and P.J.~Morrison, Phys.\ Lett.\ \textbf{375A}, 2362 (2011).} [Preview Abstract] |
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GP9.00021: Landau Damping as a General Description of Dissipation: Caldeira-Leggett and Vlasov-Poisson George Hagstrom, Philip Morrison The Caldeira-Leggett Hamiltonian describes the interaction of a discrete harmonic oscillator with a continuous bath of harmonic oscillators. This system is a standard model of dissipation in macroscopic low temperature physics, and has applications to superconductors, quantum computing, and macroscopic quantum tunneling. The similarities between the Caldeira-Leggett model and the linearized Vlasov-Poisson equation are analyzed, and it is shown that the damping in the Caldeira-Leggett model is analogous to that of Landau damping in plasmas. An invertible linear transformation is presented that converts solutions of the Caldeira-Leggett model into solutions of the linearized Vlasov-Poisson system. The idea that general dissipative systems can be described in this way is explored. [Preview Abstract] |
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GP9.00022: Magnetically Induced Transparency in Cold Magnetized Plasma by Spatially Periodic Magneto-static Field Raanan Gad, John G. Leopold, Amnon Fisher, Amiram Ron Electromagnetically Induced Transparency (EIT) is widely investigated. [1] EIT is a resonance absorption line made transparent due to destructive interference between two atomic transitions. A classical analog to quantum EIT is cold magnetized plasma, which resonantly absorbs electromagnetic radiation at the electron cyclotron frequency. Transparency is induced in such plasma by an additional magnetic field, constant in time and varying in space. [2] The proposed physical mechanism is the coupling of longitudinal plasma modulation to the transverse components of the electromagnetic radiation, canceling the forces acting on the plasma electrons. The plasma frequency and the electron cyclotron frequency are the classical analog of the atomic transition frequencies in quantum EIT. Controllable wave propagation parameters such as transmission amplitude and group velocity are some inherent features of MIT. Theoretical study and experimental results will be presented.\\[4pt] [1] K. J. Boller and S. Harris, Phys. Rev. Lett., 66, 2593 (1991).\\[0pt] [2] G. Shvets and J. S. Wurtele, Phys. Rev. Lett., 89, 115003 (2002). [Preview Abstract] |
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GP9.00023: Charged Particle Motion in Electromagnetic Fields Varying Moderately Rapidly in Space Harold Weitzner, Aukosh Jagannath For electromagnetic fields varying on the space scale of the geometric mean of the Larmor radius and the macroscopic scale length of the magnetic field lines it is shown that the magnetic moment remains an adiabatic invariant. This result is not included in the standard theories of single particle motion. The guiding center dynamics is also described and is shown to vary significantly from the normal results. The guiding center motion is along a generalized electrostatic potential surface, instead of along a magnetic field line. Under appropriate circumstances a second adiabatic invariant exists, the magnetic flux enclosed by the orbit. The usual second invariant, the longitudinal bounce integral, fails. [Preview Abstract] |
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GP9.00024: Nonlinear dispersion and adiabatic dynamics of waves with trapped particles I.Y. Dodin, N.J. Fisch A Lagrangian of a general nondissipative quasiperiodic wave in collisionless plasma is obtained in a compact form with a transparent physical meaning. Langmuir waves with trapped electrons are studied as a paradigmatic example. The general nonlinear dispersion is derived, yielding various kinetic nonlinearities as particular cases; also, the action conservation theorem is restated. In the case of deeply trapped electrons, different regimes are realized depending on the parameter $S$, which is the ratio of the energy flux carried by trapped particles to that carried by passing particles. At small $S$ the waves are stable and exhibit group velocity splitting. At large $S$ the trapped-particle modulational instability (TPMI) develops, in contrast with the existing theories of the TPMI yet in agreement with the general sideband instability theory. Remarkably, these effects are not captured by the nonlinear Schr\"odinger equation, which is traditionally considered as a universal model of wave self-action. [Preview Abstract] |
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GP9.00025: Numerical simulations of wave compression in plasma Vasily Geyko, Nathaniel Fisch When there are waves embedded in plasma, a number of curious wave phenomena arise in plasma undergoing compression. These phenomena include the amplification or damping of the waves or the transfer of wave energy or momentum to the plasma constituents. We have made preliminary studies of these compression effects through particle-in-cell simulations, both 1D and 2D, in both magnetized and unmagnetized plasmas. [Preview Abstract] |
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GP9.00026: Whistler Wave Trapping by Magnetosonic Solitons A. Tenerani, F. Califano, F. Pegoraro In the presence of inhomogeneous external fields, such as a density hump or a hole, whistler waves can be trapped for times much longer than their characteristic time scale. In space plasmas, whistler waves have been detected in the magnetosheath and inside the magnetosphere in correspondence to density humps with magnetic field minima. These structures are known as ``magnetic holes'' and have been interpreted as mirror modes. However, a different possible explanation is to consider such magnetic holes as magnetosonic solitons. Based on this second interpretation and on the ducting properties of an inhomogeneous plasma, we present a numerical study of whistler waves trapped into slow magnetosonic solitons that propagate together for very long times. We conjecture that this mechanism could be responsible for the whistler waves observed in the magnetosphere in correspondence of large scale inhomogeneous structures. [Preview Abstract] |
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GP9.00027: Parameteric studies of nonlinear oblique magnetosonic waves in two-ion-species plasmas Mieko Toida, Yuichi Kondo In a plasma containing two ion species, magnetosonic wave is split into high- and low-frequency modes. Nonliner evolution of these modes is studied by theory and simulations [1,2]. First, conditions necessary for KdV equations for low- and high- frequency modes to be valid are analytically obtained. The upper limit of the amplitude of the low-frequency-mode pulse is expressed as a function of the propagation angle $\theta$, density ratio, and cyclotron frequency ratio of the two ion species. Next, with electromagnetic particle simulations, the nonlinear evolution of a long-wavelength low-frequency-mode disturbance is examined for various $\theta$s in two plasmas with different ion densities and cyclotron frequency ratios, and the theory for the low-frequency-mode pulse is confirmed. It is also shown that if the pulse amplitude exceeds the theoretical value of the upper limit of the amplitude, then shorter-wavelength low- and high-frequency-mode waves are generated.\\[4pt] [1] M. Toida, H. Higashino, and Y. Ohsawa, J. Phys. Soc. Jpn {\bf 76}, 104052 (2007).\\[0pt] [2] M. Toida and Y. Kondo, Physics of Plasmas, {\bf 18}, 062303 (2011) [Preview Abstract] |
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GP9.00028: Studies of HF-induced Strong Plasma Turbulence at the HAARP Ionospheric Observatory J.P. Sheerin, N. Adham, N. Watanabe, B.J. Watkins, W.A. Bristow, C.A. Selcher, P.A. Bernhardt High power HF transmitters may induce a number of plasma instabilities in the interaction region of overdense ionospheric plasma. We report results from our recent experiments using over one gigawatt of HF power (ERP) to generate and study strong Langmuir turbulence (SLT) and particle acceleration at the HAARP Observatory, Gakona, Alaska. Among the effects observed and studied in UHF radar backscatter are: SLT spectra including the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, collapse, cascade and co-existing spectra, control of artificial field-aligned irregularities (AFAI), the aspect angle dependence of the plasma line spectra, and suprathermal electrons. Mapping the intensity of SLT versus pointing angle, we have discovered a number of regions of strong interaction displaced from the primary HF interaction region. Stimulated electromagnetic emission (SEE) measurements complement radar measurements. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts. [Preview Abstract] |
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GP9.00029: Debye Shielding Robert Jones We usually expect that a biased electrode in contact with a plasma will effect only its immediate surroundings. The plasma will tend to shield itself from the applied electric potential, the characteristic shielding distance being the Debye length. This is not the case for biased gun electrodes which can project a nonneutral plasma beam relatively long distances across a magnetically confined plasma (Controlling the plasma potential across a magnetic field, Trans. Kansas Acad. Sci., vol 93, pg 125, R. Jones, 1990 and Plasma heating with electrically biased plasma guns, Trans. Kansas Acad. Sci., vol 97, pg 136, R. Jones, 1994) See also my website www.robert-w-jones.com and blog www.robertwilliamjones.blogspot.com [Preview Abstract] |
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GP9.00030: Unitary Qubit Representation of Quantum and Classical Turbulence George Vahala, Bo Zhang, Linda Vahala, Min Soe A unitary qubit lattice algorithm, which scales almost perfectly to the full number of cores available (216000 cores on a CRAY XT5), is used to examine quantum turbulence and its interrelationship to classical turbulence with production runs on grids up to $5760^3$. The maximal grids achievable by conventional CFD for quantum turbulence is just $2048^3$, and artificial dissipation had to be introduced. Our unitary algorithms preserve the Hamiltonian structure of the Gross-Pitaevskii equation which describes quantum turbulence in a zero-temperature (BEC). As a result, parameter regimes have been uncovered which exhibit very short Poincare recurrence time, as well as a strong triple cascade structure in the kinetic energy spectrum, with small k-region obeying a Kolmogorov $k^{-5/3}$ spectrum The incompressible energy spectrum shows a $k^{-3}$ spectrum for large-k, but a Saffman-like $k^{-4}$ for smaller-k which is attributed to vorticity discontinuities. 2D and 3D turbulence is considered. These unitary qubit lattice algorithms are directly applicable to quantum computers. [Preview Abstract] |
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GP9.00031: Instability dynamics in photonic plasma Seth Davidovits, Laura Waller, Stefan Muenzel, Can Sun, Dmitry V. Dylov, Jason W. Fleischer It is now well-established that the nonlinear propagation of spatially incoherent light can be treated as a photonic plasma, with optical speckles interacting via Langmuir-type modulation waves. Here, we examine basic instability dynamics for different spectral distributions. In particular, we experimentally observe modulation and bump-on-tail instabilities, in both the weak and strong turbulence regimes. We directly measure momentum and energy exchange/cascades across a range of coupling strengths, including the transition between turbulence regimes. Applications to both plasma and imaging systems will be discussed. [Preview Abstract] |
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GP9.00032: Analysis and compression of six-dimensional gyrokinetic datasets using higher order singular value decomposition D. del-Castillo-Negrete, D. Hatch, P. Terry Higher order singular value decomposition (HOSVD) is explored as a tool for analyzing and compressing gyrokinetic data. An efficient numerical implementation of an HOSVD algorithm is described. HOSVD is used to analyze the full six-dimensional (three spatial, two velocity space, and time dimensions) gyrocenter distribution function from gyrokinetic simulations of ion temperature gradient, electron temperature gradient, and trapped electron mode driven turbulence. The HOSVD singular values for the velocity space coordinates decay very rapidly, indicating that only a few structures in velocity space can capture the most important dynamics. In almost all of the cases studied, HOSVD extracts velocity space structures that are very similar to orthogonal polynomials. HOSVD is also used to compress gyrokinetic datasets, an application in which it is shown to significantly outperform the more commonly used singular value decomposition. It is shown that the effectiveness of the HOSVD compression improves as the dimensionality of the dataset increases. [Preview Abstract] |
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GP9.00033: Exact momentum conservation laws for the gyrokinetic Vlasov-Poisson equations Alain Brizard, Natalia Tronko The exact momentum conservation laws for the nonlinear gyrokinetic Vlasov-Poisson equations are derived by applying the Noether method on the gyrokinetic variational principle [A.~J.~Brizard, Phys.~Plasmas {\bf 7}, 4816 (2000)]. From the gyrokinetic Noether canonical-momentum equation derived by the Noether method, the gyrokinetic parallel momentum equation and other gyrokinetic Vlasov-moment equations are obtained. In addition, an exact gyrokinetic toroidal angular-momentum conservation law is derived in axisymmetric tokamak geometry, where the transport of parallel-toroidal momentum is related to the radial gyrocenter polarization, which includes contributions from the guiding-center and gyrocenter transformations. [Preview Abstract] |
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GP9.00034: Gyrokinetic Fokker-Planck Collision Operator Bo Li, Darin Ernst The gyrokinetic linearized full Fokker-Planck operator is obtained for delta-f gyrokinetic simulations, including finite Larmor radius corrections [1]. The new operator is exact within the usual gyrokinetic and Fokker-Planck orderings, and treats collisions between arbitrary masses. Finite Larmor radius (FLR) effects in the collision operator play an important role in plasma turbulence and transport, such as strongly reducing the growth rates of trapped electron modes at short wavelengths [2] and in collisional damping of zonal flows [3], relevant near marginal stability. The FLR terms provide physical dissipation needed to achieve steady state in gyrokinetic simulations [4]. The operator includes both the test-particle and field-particle terms and thus automatically satisfies the conservation properties and Boltzmann's H-theorem. \\[4pt] [1] B. Li and D.R. Ernst, Phys. Rev. Lett. 106, 195002 (2011).\\[0pt] [2] D.R. Ernst et al., in Proc. 20th IAEA Fusion Energy Conference, Chengdu, China (IAEA-CN-149/TH/1-3, 2006).\\[0pt] [3] P. Ricci et al.,Phys. Plasmas 17, 072103 (2010).\\[0pt] [4] M. Barnes et al., Phys. Plasmas 16, 072107 (2009). [Preview Abstract] |
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GP9.00035: Algorithmic improvements in the Trinity, GS2, Gryffin, AstroGK(S) suite of codes William Dorland, Anjor Kanekar, Michael Barnes We present an overview of major upgrades to the family of gyrokinetic codes that includes... {\bf Trinity:} Time-dependent gyrokinetic transport, integrated with numerous gyrokinetic turbulence and stability codes, including Gryffin (below). {\bf GS2:} Widely used gyrokinetic turbulence and stability code. {\bf Gryffin:} Gyrofluid turbulence and stability code, with new closure to model the effects of the nonlinear cascade of free energy on low-order fluid moments. {\bf AstroGK(S):} Gyrokinetic turbulence code derived from GS2; toroidal geometry removed to accelerate development and applications for non-toroidal systems (such as the solar wind). The fully spectral version (AstroGKS) will be presented in some detail. [Preview Abstract] |
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GP9.00036: Scale-dependent anisotropy in gyrokinetic turbulence Anjor Kanekar, William Dorland, Alexander Schekochihin Eddies in Alfvenic turbulence get progressively more elongated along the field line at small scales. To date, this has not been observed in gyrokinetic simulations. We present diagnostics of gyrokinetic simulations of Alfvenic and Kinetic Alfvenic turbulence at high beta [Howes et al., PRL, 107:035004:2011]. Our diagnostics follow [Chen et al. PRL, 104:255002:2010], who focused on the importance of the anisotropy dependence on the \textit{local} magnetic field. We explore the validity of Chen et al.'s approach theoretically and with model data, and apply such diagnostics to the study of Alfven and Kinetic Alfvenic turbulence. [Preview Abstract] |
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GP9.00037: Number-conserving linear reponse study of low-velocity ion stopping in a collisional magnetized classical plasma Hrachya B. Nersisyan, Claude Deutsch, A.K. Das The results of a theoretical investigation on the low-velocity stopping power of the ions moving in a magnetized and collisional plasma are discussed [1]. The stopping power for an ion is calculated through linear response theory (LRT) with a dielectric function approach. Collisions, leading to a damping of the plasma excitations are taken into account with a number-conserving relaxation time approximation within LRT. In order to highlight the combined effects of collisions and magnetization, we compare analytical and numerical results derived for a nonzero damping and magnetic field to those with none. It is thus demonstrated that collisions remove the anomalous friction obtained previously [2] for collisionless magnetized plasmas at low ion velocities. One of our main goals is to contrast present theoretical results with those derived from a novel diffusion formulation based on the one-component plasma hydromodes respectively framed on target ions and electrons [3].\\[4pt] [1] H.B. Nersisyan, C. Deutsch and A.K. Das, Phys. Rev. E83, 036403 (2011)\\[0pt] [2] H.B. Nersisyan, Phys. Rev. E61, 7022 (2000)\\[0pt] [3] C. Deutsch and R. Popoff, Phys. Rev. E78, 056405 (2008) [Preview Abstract] |
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GP9.00038: Gyrokinetic Studies of Microtearing Modes in the Reversed Field Pinch Daniel Carmody, Varun Tangri, P.W. Terry Linear gyrokinetic simulations are performed using the GYRO code modified for RFP equilibria. It is shown that a transition occurs between ITG at low electron $\beta$ to microtearing modes as $\beta_e$ increases. Initially the two modes occur at the same length scales, but as $\beta_e$ increases there is a shift of the microtearing modes to smaller scales. The critical $\beta_e$ value for the switchover between the two modes is approximately 4.5\%, a characteristic value for standard discharges of the Madison Symmetric Torus, indicating that both ITG and microtearing may be important for these runs, while PPCD discharges are more likely to be exclusively in the microtearing dominant regime. We investigate the dependence of the microtearing modes on a variety of parameters including electron temperature gradient, temperature ratio, and collisionality. We find the critical temperature gradient for instability to be $a/L_{te} \sim 3$. We also find evidence for a collisionless microtearing regime, possibly associated with negative shear, and we compare these results with theoretical predictions. [Preview Abstract] |
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GP9.00039: High-n tearing-parity modes in toroidal geometry William Nevins We attempt to elucidate how effects associated with toroidal geometry generate parallel currents through mechanisms absent in slab or cylindrical geometry. In particular, we find that the presence of geodesic curvature introduces a novel mechanism for generating a parallel acceleration from perpendicular electric fields. This effect may be important to the effectiveness of nearly electrostatic tearing-parity modes in generating magnetic stochasticity; the (previously unexpected) instability of micro-tearing modes at low aspect ratio [2, 3]; as well as the unexpectedly large current-channel width observed in recent simulations of microtearing modes [4].\\[4pt] [1] W.M. Nevins et al, PRL $<$106$>$, 065003 (2011). \newline [2] M. Kotschenreuther et al, Nucl. Fusion $<$40$>$, 677 (2000). \newline [3] D.J. Applegate et al, Phys. Plasmas $<$11$>$, 5085 (2004). \newline [4] W. Guttenfelder et al, PRL $<$106$>$, 155004 (2011). [Preview Abstract] |
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GP9.00040: Analysis of the nullspace of the MHD force operator in the SIESTA equilibrium code S.P. Hirshman, C.R. Cook, R. Sanchez SIESTA is a three-dimensional magnetohydrodynamics equilibrium code capable of resolving magnetic islands in toroidal plasma confinement devices. The linearized MHD force operator used in the code contains an approximate nullspace of eigenmodes with extremely small eigenvalues. Physically, these correspond to displacements that result in essentially no change in the ideal MHD energy. It will be shown that these modes are aligned with the magnetic field throughout the plasma volume, except in tiny transition layers. As a result, there is a large degeneracy of states that give similar insignificant changes to the energy. These correspond to the least stabilizing modes in a closed, nested flux surface topology. Until a non-ideal perturbation is applied, these nullspace modes that are parallel to the magnetic field will dominate the plasma displacement direction in a nonlinear energy minimization technique such as that used in SIESTA. The eigenmodes will be shown throughout the plasma volume, and the effects on the spectrum of the different convergence techniques used in SIESTA will be discussed. The results give confirmation to analytical methods used to minimize the MHD energy. [Preview Abstract] |
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GP9.00041: Extending SIESTA capabilities: removing field-periodic and stellarator symmetric limitations C.R. Cook, S.P. Hirshman, R. Sanchez, D.T. Anderson SIESTA is a three-dimensional magnetohydrodynamics equilibrium code capable of resolving magnetic islands in toroidal plasma confinement devices. Currently SIESTA assumes that plasma perturbations, and thus also magnetic islands, are field-periodic. This limitation is being removed from the code by allowing the displacement toroidal mode number to not be restricted to multiples of the number of field periods. Extending SIESTA in this manner will allow larger, lower-order resonant islands to form in devices such as CTH. An example of a non-field-periodic perturbation in CTH will be demonstrated. Currently the code also operates in a stellarator-symmetric fashion in which an ``up-down'' symmetry is present at some toroidal angle. Nearly all of the current tokamaks (and ITER in the future) operate with a divertor and as such do not possess stellarator symmetry. Removal of this symmetry restriction requires including both sine and cosine terms in the Fourier expansion for the geometry of the device and the fields contained within. The current status of this extension of the code will be discussed, along with the method of implementation. [Preview Abstract] |
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GP9.00042: Resistive interchange modes and plasma flow structures Roberto Paccagnella Interchange modes are ubiquitous in magnetic confinement systems and are likely to determine or influence their transport properties. For example a good agreement between theory predictions for linear interchange modes and experimental results has been found recently [1] in a Reverse Field Pinch device. In this work a set of magneto-hydro-dynamic (MHD) equations that describe the dynamical evolution for the pressure driven interchange modes in a magnetic confinement system are studied. Global and local solutions relevant for tokamaks and Reversed Field Pinches (RFPs) configurations are considered. The emphasis is especially in the characterization of the plasma flow structures associated with the dominant modes. \\[4pt] [1] M. Zuin et. al., Nucl. Fusion \textbf{50} (2010) 52001. [Preview Abstract] |
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GP9.00043: Magnetorotational instability and a generalized energy principle Natalia Tronko, Philip J. Morrison, Emanuele Tassi The Magnetorotational Instability (MRI) is believed to play a crucial role in transferring angular momentum, particularly in the context of accretion discs where it is important for allowing star formation. This is why, previous work was concentrated on studying nonlinear mechanisms for MRI saturation. Therefore, conditions for marginal stability of general equilibria are important to investigate. Here we do so by using the noncanonical Hamiltonian approach [1], providing variational principles for equilibria that is used to assess stability. We show that a two-dimensional MRI model [2] is an infinite-dimensional noncanonical Hamiltonian system. The noncanonical Poisson bracket is identified and shown to obey the Jacobi identity, and families of Casimir invariants are obtained. From these, explicit sufficient conditions for the energy stability of two classes of equilibria are obtained by means of the Energy-Casimir method. The presence of an equilibrium azimuthal magnetic field is shown not to introduce destabilizing effects. A direct analogy is found between terms in the expression of the second variation of the free energy and terms appearing in usual energy principle analysis of compressible reduced MHD for tokamaks. \\[4pt] [1] P.~J.~Morrison, Rev.~Mod.~Phys., {\bf 70}, 467 (1998). \\[0pt] [2] K.~Julien and E.~Knobloch, Phil. Trans.\ Roy.\ Soc., {\bf 386A}, 1607 (2010) [Preview Abstract] |
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GP9.00044: Spectra of two-dimensional MHD plasmas forced by power-law noise Chang-Bae Kim If magneto-hydrodynamic plasmas of two dimensions are forced at an intermediate scale, phenomenological arguments assert the existence of two inertial regimes. One is where the square of the magnetic potential cascades to larger scales and, in the other, the energy is transferred to smaller scales down to the dissipation range. Numerous simulations provide sufficient evidence to endorse such prediction. In both regimes the spectral exponent of relevant quantities are generally independent of the specifics of the forcing, for example, the power of the noise spectrum. Renormalization-group (RG) idea offers a more sophisticated approach in elucidating the spectral behaviors of the forced MHD plasmas. RG, however, predicts the strong dependence of the spectral exponent on the power of the noise spectrum. The main focus of the present work is to reconcile the difference between the two approaches by performing numerical simulations. [Preview Abstract] |
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GP9.00045: Control of MHD instabilities in the STOR-M tokamak Chijin Xiao, Sayf Elgriw, Akira Hirose Experiments to control the MHD activities have been carried out through compact torus injection (CTI) and resonant helical coils (RHC) on the STOR-M tokamak. The MHD instabilities have been measured by Mirnov coil arrays and miniature soft X-ray (SXR) pin-hole cameras. The data have been analyzed by singular value decomposition algorithm and the spatial Fourier harmonic analysis. Injection of a high density compact torus into STOR-M induced a transient phase with reduced $m$ = 2 Mirnov oscillation amplitude. After appearance of an $m$ = 1 gong mode burst the $m$ = 2 oscillation amplitude returned to its nominal level before CTI. In the RHC experiments, an $m$ = 2 helical coil was wound outside the vacuum chamber and powered by a capacitor bank through an IGBT switch. A current pulse of a few milliseconds was applied to RHC during the plasma current plateau. Once the current amplitude reaches a threshold level, the $m$ = 2 MHD oscillation level was significantly reduced. Addition of equilibrium poloidal magnetic field calculated by TOSCA code, an assumed magnetic island perturbation, and the vacuum magnetic field produced by RHC also showed that the island can be eliminated when the RHC current reached a certain level. [Preview Abstract] |
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GP9.00046: Energy stability for symmetric MHD equilibria in the Eulerian description T. Andreussi, F. Pegoraro, P.J. Morrison Magnetized plasma flows with symmetry are analyzed by exploiting the noncanonical Hamiltonian formulation of magnetohydrodynamics (MHD).\footnote{P.J.~Morrison, J.M.~Greene, Phys.~Rev.~Lett., \textbf{45} 790 (1980); \textbf{48} 569 (1982); P.J.~Morrison, Rev.~Mod.~Phys., \textbf{70} 467 (1998).} Because of the symmetry, a flux function is introduced and, by assuming entropy is a flux function, a complete set of Casimir invariants is determined. Translational, axial, and helical symmetries are considered.\footnote{T.~Andreussi, P.J.~Morrison, F.~Pegoraro, Plasma Phys.~Contr.~Fus., \textbf{52} 055001 (2010).} The energy-Casimir (Eulerian) variational principle for equilibria is analyzed. It is shown that extremal points correspond to equilibria of the symmetric MHD systems, which in the axial symmetric case correspond to the solutions of the generalized Grad-Shafranov equation. For generic equilibria, the second variation of the energy-Casimir functional is presented. A stability matrix is obtained and brought to diagonal form. Positiveness of the second variation is analyzed and a general set of sufficient conditions for stability of the equilibria is deduced. Results are further improved by using\ a Poincar\`{e} inequality, and comparison to the conventional energy principle is made. [Preview Abstract] |
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GP9.00047: Hamiltonian structure of magnetofluid models with gyroviscous-like contributions Alexander Wurm, P.J. Morrison, Richard Hazeltine Magnetofluid theories, like MHD, can be expressed in terms of Eulerian (or spatial) variables, or in terms of Lagrangian (or material) variables. The former formulation generally exhibits a noncanonical Hamiltonian structure [1]. Building on the work of Ref. [2] we generalize the gyromap to three dimensional magnetofluid theories. Starting with the 3D ideal MHD noncanonical Poisson bracket [1] and a Hamiltonian including general gyroviscous terms, we derive equations of motions and compare them to, e.g., Braginskii [3] in the collisionless limit. In addition we explore the Lagrangian version of these theories which use Hamilton's principle to derive the equations of motion [4]. \\[4pt] [1] P.J.~Morrison and J.M.~Greene, Phys. Rev. A {\bf 45},790 (1980).\\[0pt] [2] P.J.~Morrison, I.L.~Caldas, and H.~Tasso, Z. Naturforsch. {\bf 39a}, 1023 (1984).\\[0pt] [3] S.I.~Braginskii, in {\it Review of Plasma Physics}, ed. M.A.~Leontovich (Consultants Bureau, New York, 1965), Vol. 1, p. 205.\\[0pt] [4] W.A.~Newcomb, Nuclear Fusion: 1962 Suppl. Part 2, p. 451. [Preview Abstract] |
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GP9.00048: Nonlinearly unstable interchange modes in transverse magnetic field Jupiter Bagaipo, P.N. Guzdar, A.B. Hassam The nonlinear stability of the ideal MHD interchange mode immersed in a constant transverse magnetic field near marginal conditions is studied. We used reduced equations for a strong axial field to show a way to calculate an analytic solution for the nonlinear behaviour as a function of the deviation from marginality. The result could find application in assessing the B-field tolerances in stellarator coil design. A perturbation analysis in the smallness parameter, $|b_2/B_c|^{1/2}$, is carried out, where $B_c$ is the critical transverse magnetic field for the zero-frequency ideal mode, and $b_2$ is the deviation from $B_c$. The lowest order expansion yields an eigenvalue equation for the magnitude of the critical field required for marginality, $B_c$. The calculation is carried out to third order, including nonlinear terms, where a time-evolution equation for the amplitude is found. In the short wavelength limit we find that the system is nonlinearly unstable for large enough perturbations even if $b_2/B_c>0$ (linearly stable) and the amplitude will grow without saturation. This result is similar to those of Cowley and Artun (Physics Reports 1997) for the marginally stable line-tied $g$-mode. We found the normalized amplitude for the instability to scale as $|b_2/B_c|^{1/2}$. Nonlinear numerical simulations of this system in dissipative MHD have verified the result in our calculations. Work supported by the USDOE. [Preview Abstract] |
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GP9.00049: The limit of Hall-MHD equilibria for a small hall effect Eliezer Hameiri The question of what is the limit of a Hall-MHD equilibrium as the Hall parameter (the ratio of the ion skin depth to a macroscopic length scale) becomes vanishingly small, was treated by some authors, and it was found that a certain limiting process leads to a classical MHD equilibrium with mass flow. However, the precise MHD equilibrium was not identified. We are able to identify the limiting state exactly, which enables us which enables us to generate Hall-MHD equilibria perturbatively as an expansion in the typically small Hall parameter. The benefit here is that rather than using the Hall-MHD equilibrium equations, which consist of two coupled Grad-Shafranov equations in two flux functions, we have to solve for the MHD equilibrium state, after which there is a linear system of equations to solve for the perturbation. Our entire work is based on variational formulations of the various equations involved, so perturbed equations can be solved numerically as minimum problems. Unlike common practice, we allow for finite electron pressure throughout this work. [Preview Abstract] |
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GP9.00050: Two-dimensional axisymmetric and three-dimensional helical equilibrium in the line-tied screw pinch Carlos Paz-Soldan, M.I. Brookhart, A.J. Clinch, D.A. Hannum, C.B. Forest The line-tying condition at a conducting anode is shown to provide a localized modification to the well-understood 1-D screw pinch equilibrium in the presence of bulk plasma diamagnetism. Diamagnetic currents cannot flow near the conducting anode and are measured to disappear in a localized boundary layer, causing a weak mirror configuration that breaks 1-D equilibrium and causes large parallel pressure gradients suggestive of significant radial outflows. For sufficiently large plasma currents, the paramagnetic nature of parallel current drives the equilibrium to paramagnetism and destroys the mirror effect. At a critical plasma current the axisymmetric equilibrium is found to transition to a long-lived, rotating, helical 3-D equilibrium state. Internal measurements of this state via multi-point correlation analysis techniques illustrate that it preserves the flux surfaces and pressure profile of the axisymmetric equilibrium. Measurements indicate that despite the fact that the flux surfaces wander at the anode, the line-tied boundary conditions are not necessarily violated. [Preview Abstract] |
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GP9.00051: Stability of a Zero-Net Current Line-Tied Screw Pinch Matthew Brookhart, Carlos Paz-Soldan, Cary Forest The internal kink instability in the Rotating Wall Machine (RWM) has an ideal character, but also exhibits reconnection events that periodically flatten the current profile and change the magnetic topology. The line-tied boundary conditions present an ideal analogue to coronal loop and solar flare physics. Internal measurements of B, J, and V$_z$ have been extensively gathered in the screw-pinch geometry. Through shot-to-shot averaging 2D equilibrium profiles and steady-state merger of current filaments are measured. The line-tying conditions in the RWM are examined through the structure of the measured magnetic field. Theories of coronal loop formation and stability indicate that current in coronal loops may be created by twisting vortices in the photosphere at the line-tied footprints of loops. Such convection necessarily creates a coaxial current structure where current on axis flows oppositely to current at larger radii. To study the equilibria and MHD stability of these ``Zero Net Current'' structures, the modular current injection scheme on the RWM has been modified to allow coaxial current injection. Construction and preliminary results from these studies are presented. [Preview Abstract] |
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GP9.00052: Sawtooth activities in the Ohmic heated J-TEXT plasmas Xiande Feng, Ge Zhuang, Xiaoqing Zhang Benefiting from a few powerful analyzing tools to manipulate the measured data by a set of soft X-ray emission detector arrays (SXRs) on the J-TEXT tokamak (Formerly TEXT-U tokamak, Bt=3T, and Ip=350kA), the sawtooth behaviors such as period and inverse radius can be carefully excavated under different discharge parameters. Especially, the transition between sawteeth and Mirnov oscillations, which have been clearly shown in the traces of SXRs and magnetic sensors on J-TEXT, can be interpreted based on some numerical simulation results, such as the anti-correlation effect. Furthermore, some discharges ended with a disruption, along with this transition strong coupling between the m=1 and m=2 MHD modes could be the main mechanism leading to the disruption. In addition to these events, the experimental observations manifest there is a concurrence of sawtooth and Mirnov oscillations in some discharges, whereby the sawtooth collapse is evidently independent of the m=1 oscillation. The investigation of stimulation of sawtooth phase changing in all SXR channels in case of neon gas puffing is undertaking. [Preview Abstract] |
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GP9.00053: Multiple timescale calculations of sawteeth in tokamak plasmas S.C. Jardin, N. Ferraro, J. Breslau, J. Chen We present results of using M3D-$C^{1}$ [1] to perform 3D nonlinear magnetohydrodynamics calculations of a tokamak plasma that span the timescales associated with ideal and resistive stability as well as parallel and perpendicular transport. We specify the transport coefficients and apply a ``current controller'' that adjusts the boundary loop-voltage to keep the total plasma current fixed. Depending on the transport model, the plasma either reaches a stationary quasi-helical state in which the central safety factor is approximately unity, or it periodically undergoes sawtooth oscillations [2] with a period that approaches a constant value. These calculations have been performed both in a ``fixed boundary'' configuration with a wall on the plasma boundary as well as in a ``free boundary'' configuration with a separatrix surrounded by a scrape-off-layer plasma with open field lines and a resistive wall. We have performed series of runs to determine the dependence of the sequence on the form and magnitude of the resistivity, parallel and cross-field thermal conductivity, and viscosity. We are presently investigating the effect of the plasma shape on the sawtooth behavior, and the effects of two-fluid terms on the dynamics. \\[4pt] [1] J. Breslau, N. Ferraro, S. Jardin, Physics of Plasmas 16 092503 (2009) \\[0pt] [2] X. von Goeler, W. Stodiek, and N. Sauthoff, Phys. Rev. Lett. 33, 1201 (1974) [Preview Abstract] |
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GP9.00054: Double adiabatic theory of driven collisionless geodesic acoustic modes (GAMs) in toroids Adil Hassam, Robert Kleva The GAM is an axisymmetric oscillation of a toroidal magnetically confined plasma, resulting from an interplay between poloidal plasma rotation and perpendicular flux tube compression from the B field gradient. The frequency is super-parallel-sonic, ie, omega $\sim $ (ion thermal speed)/R, greater than the parallel acoustic mode which is lower by a factor of q. Consequently, collisionless geodesic acoustic modes in tokamaks can be described by the Chew-Goldberger-Low double-adiabatic fluid closures. This allows a simpler nonlinear formulation. We use these equations to study driven, collisionless GAMs in tokamaks. The motivation for this study is a proposal by Hallatschek and McKee to drive GAMs on the D3D tokamak at resonance. The drivers in the CGL theory include external magnetic forces to effect flux surface displacements as well as sources to provide modulated non-axisymmetric ion heating. We show that the linear mode frequency from CGL theory agrees with previous kinetic results. Comparisons will be made between different approaches to resonate the mode. Nonlinear effects will be evaluated. A 2D toroidal numerical simulation of driven GAMs is in progress. [Preview Abstract] |
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GP9.00055: ITER AND MAGNETIC FUSION DEVELOPMENT, PLASMA CONFINEMENT CONFIGURATIONS, STELLARATOR |
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GP9.00056: Scoping Studies for an Integrated PMI-PFC Test Facility S.C. Prager Innovative plasma facing components (PFCs) are needed for next-step fusion experiments and beyond, and can be most efficiently developed in a dedicated test facility. In scoping studies for such a facility, we have considered a range of sources (to provide high heat fluxes to target PFCs to simulate the plasma-material interaction) and a variety of PFCs to be exposed. We have investigated sources ranging from small low-field devices for basic science studies to a 1/4 torus with the size and field of the NSTX upgrade outfitted with a source that provides 10 to 40 MW/m2 for 5 seconds. Aiming toward solutions for DEMO-level PFCs, concepts that have been considered for testing include slow-flowing capillary-restrained lithium PFC modules, thick fast-flowing liquid walls and jets, and active PFC coatings and engineered solid surfaces. Extensive surface and plasma diagnostics, as well as modeling such as liquid metal MHD, will be needed to extrapolate the results to future tokamaks. [Preview Abstract] |
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GP9.00057: Exploration of steady-state scenarios for the Fusion Development Facility (FDF) V.S. Chan, A.M. Garofalo, R.D. Stambaugh, M. Choi, J.E. Kinsey, L.L. Lao, P.B. Snyder, H.E. St. John, A.D. Turnbull A Fusion Nuclear Science Facility (FNSF) has to operate at $10^5$ times longer duration than that of present tokamak discharges. The scalability of plasma sustainment to such a long time is an issue that needs to be resolved by scientific understanding. We carry out steady-state (SS) scenario development of the FDF (a candidate for FNSF-AT) using an iterative process toward a self-consistent solution via alternating temperature profiles and current profile evolution. The temperature profile evolves according to a physics-based transport model GLF23. SS requires large off-axis current drive (CD). To achieve this with no NBI is highly challenging. It however simplifies tritium containment, increases area for tritium breeding, and avoids costly negative-ion NBI technology. We find that with ECH/ECCD only, too much power is required. A SS baseline equilibrium is found by adding LHCD: $Q_{fus}\sim 4$, $H_{98y2}\sim 1.2$, $f_{BS}\sim 70$\%, $P_{fus}\sim 260$ MW, $P_{EC} =35$ MW, $P_{LH} =21$ MW. The GATO ideal MHD code finds the equilibrium stable to $n=1$ internal kink at $\kappa =2.3$. [Preview Abstract] |
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GP9.00058: Fusion Nuclear Science Facility (FNSF) motivation and required capabilities Y.K.M. Peng, J.M. Park, J.M. Canik, S.J. Diem, A.C. Sontag, A. Lumsdaine, M. Murakami, Y. Katoh, T.W. Burgess, K. Korsah, B.D. Patton, J.C. Wagner, G.L. Yoder, M.J. Cole, P.J. Fogarty, M. Sawan A compact (R$_{0}\sim $1.2-1.3m), low aspect ratio, low-Q ($<$3) Fusion Nuclear Science Facility (FNSF) was recently assessed to provide a fully integrated, D-T-fueled, continuously driven plasma, volumetric nuclear environment of copious neutrons. This environment would be used to carry out, \textit{for the first time}, discovery-driven research in fusion nuclear science and materials, in parallel with and complementary to ITER. This research would aim to test, discover, and understand new nuclear-nonnuclear synergistic interactions involving plasma material interactions, neutron material interactions, tritium fuel breeding and transport, and power extraction, and innovate and develop solutions for DEMO components. Progress will be reported on the fusion nuclear-nonnuclear coupling effects identified that motivate research on such an FNSF, and on the required capabilities in fusion plasma, device operation, and fusion nuclear science and engineering to fulfill its mission. [Preview Abstract] |
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GP9.00059: A primary investigation of the concept of a throttled tokomak Yian Lei, Xiaofei Ji, Jianguo Chen The technical challenges and economical issues of an ITER sized tokomak are among the main concerns of the feasibility of commercial fusion reactor. We believe an asymmetric throttled tokomak by increase the magnetic field strength a few times higher in a small section of the plasma torus can ease some of the issues by lowering down the parameters of the fusion plasma in the majority volume and raising the temperature in the throttled region. The low parameter plasmas are easier to be confined, heated up, and externally drive a current. The limited fusion region makes the protection and energy retrieving simpler. The asymmetry of the tokomak can also suppress many MHD instabilities. We are investigating the behavior of the plasmas in the vicinity of the throttle neck, including the mirroring effects, global electric charge displacement, particle acceleration in a toroidal magnetic field, and temperature and density profile changes. The trajectory and acceleration of single particles are calculated with a simplified current profile. [Preview Abstract] |
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GP9.00060: Development of the ITER ICH Transmission Line and Matching System D.A. Rasmussen, R.H. Goulding, P.V. Pesavento, B. Peters, D.W. Swain, E.H. Fredd, J. Hosea, N. Greenough The ITER Ion Cyclotron Heating (ICH) System is designed to couple 20 MW of heating power for ion and electron heating. Prototype components for the ITER Ion Cyclotron Heating (ICH) transmission line and matching system are being designed and tested. The ICH transmission lines are pressurized 300 mm diameter coaxial lines with water-cooled aluminum outer conductor and gas-cooled and water-cooled copper inner conductor. Each ICH transmission line is designed to handle 40- 55 MHz power at up to 6 MW/line. A total of 8 lines split to 16 antenna inputs on two ICH antennas. Industrial suppliers have designed coaxial transmission line and matching components and prototypes will be manufactured. The prototype components will be qualified on a test stand operating at the full power and pulse length needed for ITER. The matching system must accommodated dynamic changes in the plasma loading due to ELMS and the L to H-mode transition. Passive ELM tolerance will be performed using hybrid couplers and loads, which can absorb the transient reflected power. The system is also designed to compensate for the mutual inductances of the antenna current straps to limit the peak voltages on the antenna array elements. [Preview Abstract] |
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GP9.00061: Mode Content Analysis for ITER gyrotron ECH Transmission Lines Elizabeth Kowalski, Michael Shapiro, Richard Temkin, Timothy Bigelow, David Rasmussen The Electron Cyclotron Resonance Heating system for ITER will require 20 MW of power from 24 1-MW gyrotrons at 170 GHz. Over-moded corrugated circular waveguides must transport this power with less than 14\% loss. Launchers at the end of the waveguide into the tokamak require high precision alignment of the beam power. Small percentages of higher order mode content can cause a significant offset and tilt of the beam at the end of the waveguide, inhibiting the accuracy of the launchers. An analysis of mode content in transmission lines and mode conversion due to miter bends is necessary. We propose the use of two consecutive miter bends in the transmission line to mode convert a significant fraction of the unwanted higher order mode content into the fundamental HE$_{11}$ mode. In order to properly shape these miter bend mirrors, the amplitude of the higher order modes must be known. We will present results showing that the LP$_{11}$ mode content can be greatly reduced by tilting two consecutive miter bend mirrors. [Preview Abstract] |
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GP9.00062: Status of ECE Diagnostics for ITER Richard Ellis, Max Austin, Perry Phillips, William Rowan, Joseph Beno, Russell Feder, Amanda Hubbard, Hitesh Pandya ECE on ITER will be used to measure electron temperature profiles and non thermal features of the distribution. The diagnostic has two systems. One is radial, primarily for temperature profile measurement ; the other views at a small oblique angle and will be dedicated to measuring non-thermal emission. Radiation will be conducted to the diagnostic area by corrugated waveguide, dielectric waveguide, or quasioptical chains. Emission will be measured with a multichannel Michelson interferometer which provides wide wavelength coverage, and two microwave radiometers which cover the fundamental and second harmonic ECE (X and O mode) and have excellent time resolution. In-situ calibration employs a hot calibration source which has been designed, constructed, bench tested, and will be installed on two other tokamaks. We report extensive wideband transmission measurements made on the DIII-D Michelson corrugated waveguide system as well as preliminary measurements on sections of ITER size waveguide. [Preview Abstract] |
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GP9.00063: Modelling controlled VDE's and ramp-down scenarios in ITER L.L. LoDestro, R.A. Kolesnikov, W.H. Meyer, L.D. Pearlstein, D.A. Humphreys, M.L. Walker Following the design reviews of recent years, the ITER poloidal-field coil-set design, including in-vessel coils (VS3), and the divertor configuration have settled down. The divertor and its material composition (the latter has not been finalized) affect the development of fiducial equilibria and scenarios together with the coils through constraints on strike-point locations and limits on the PF and control systems. Previously we have reported on our studies simulating controlled vertical events in ITER with the JCT 2001 controller to which we added a PID VS3 circuit. In this paper we report and compare controlled VDE results using an optimized integrated VS and shape controller in the updated configuration. We also present our recent simulations of alternate ramp-down scenarios, looking at the effects of ramp-down time and shape strategies, using these controllers. [Preview Abstract] |
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GP9.00064: Characterization of Plasma Gun with TiH$_{2}$/C$_{60}$ Cartridge for Disruption Mitigation in Tokamaks I.N. Bogatu, J.R. Thompson, S.A. Galkin, J.S. Kim Impurity injection for disruption mitigation in tokamaks must be faster than growth time of plasma instabilities, requires sufficient mass to get critical electron density, high penetrability, and large assimilation fraction in the core plasma, with rapid impurity redistribution over the whole plasma. FAR-TECH, Inc. proposed the innovative idea to use hyper-velocity ($>$30 km/s), high-density ($>$10$^{23}$~m$^{-3})$ C$_{60}$/C plasma jets with high ram pressure to deliver the impurity mass in $<$1 ms. For this purpose C$_{60}$ powder explosively sublimated into molecular gas, from a solid state, pulsed power driven TiH$_{2}$/C$_{60}$ injector cartridge is ionized and accelerated in a plasma accelerator. We report the complete characterization of the TiH$_{2}$/C$_{60}$ cartridge with 5 kJ capacitive driver which demonstrated the capability of producing $>$30 mg of C$_{60}$ gas in $<$0.5 ms. In addition we present the construction and testing status of a 100 kJ coaxial plasma gun ($\sim $35 cm length) prototype with TiH$_{2}$/C$_{60}$ cartridge for a small scale, proof-of-principle experiment on a tokamak. [Preview Abstract] |
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GP9.00065: Adoption of $\bf{MgB_2}$ Large Superconducting Coils in Ignitor* G. Grasso, R. Penco, B. Coppi The superconducting material $MgB_2$ is found to be compatible with the cooling system of the current Ignitor design consisting of He-gas flow at about 30 K, although $MgB_2$ may use colder gas at 10-15 K. The two outer poloidal field coils have been considered as their main requirements can be met, in principle, by commercially available $MgB_2$ strands. Both the technical feasibility of these coils, as well as their stability and protection in the unlike case of its quench have been studied. Accordingly, the $MgB_2$ wire technology available from Columbus Superconductors is sufficient to achieve the target specifications for the considered coils (about 5 meters of outer diameter, and maximum field on the conductor of 4.7 T). Moreover, the relevant cable in conduit design, for the $MgB_2$ conductor including about 300 strands of 1 mm in diameter each, allows the system to maintain its temperature within 0.1 K of the He flow temperature. The stability of the $MgB_2$-based coils has been successfully verified as being practically insensitive to rare energy release events typically due to imperceptible cable movements, or microcracks in the epoxy impregnation. These are typical sources of severe instabilities in traditional superconducting magnets. Adopting materials such as $MgB_2$ is an important step toward achieving better duty cycles in experiments of the Ignitor type with a simplified cooling technology compared to that for traditional superconductors.*Sponsored in part by ENEA of Italy. [Preview Abstract] |
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GP9.00066: Fabrication Phase of the Ignitor Program* S. Mantovani, P. Frosi, G. Ramogida, B. Coppi The fabrication phase of the complete Ignitor machine has started by identifying at first the main industrial groups that have the capabilities to construct the main components of the machine. The ``translation'' of the drawings of the detailed design into fabrication drawings has been undertaken reconsidering the results of the structural analysis that has been carried out for all the machine elements. A special attention is being devoted to the robotic systems that have to be able to perform different functions during the final assembly of the machine and for its operation. The management structure necessary to carry out the entire fabrication effort has been established. The Italian Space Agency (A.S.I.) has been charged with the task of administrating the funds allocated for the construction of the core of the machine by the Italian government. *Sponsored in part by the U.S. DOE. [Preview Abstract] |
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GP9.00067: The IGNIS* Collaboration in the Broader Context of Fusion and Space Research** E. Azizov, B. Coppi, E. Velikhov, A. Airoldi, F. Bombarda, A. Cardinali, G. Cenacchi, P. Detragiache, G. Grasso, S. Mantovani, G. Rubinacci The IGNIS collaboration has the purpose to construct and operate the high field Ignitor machine designed to investigate D-T fusion burning plasmas close to ignition conditions, and is based on the decision by Italy and Russia to fund the relevant program jointly. The Troitzk site has been chosen in view of the important facilities that it has for D-T burning machines and of the outstanding tradition of accomplishments by the Kurchatov Institute that will be in charge of the machine operation. Building upon the existing talents in Italy and in Russia, the Ignitor program has been formulated in the broader context of the physics of high energy plasmas both in astrophysics and in the laboratory. This (also funded) initiative, welcomed by the international community that is active in both fields, is reflected in the high level scientific committee that advises the Ignitor program and by the results presented at the three interdisciplinary meetings held in Italy and Russia since 2010. New projects motivated by the IGNIS collaborations (e.g. concerning the diagnostics systems, and EC edge heating) are presented. *Ignis = fire in Latin; **Sponsored in part by KIAE, MIUR and CNR of Italy, and by the U.S. DOE. [Preview Abstract] |
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GP9.00068: Toward a possible mitigation of VDEs in IGNITOR* R. Albanese, G. Ambrosino, A. Pironti, G. Rubinacci, F. Villone, G. Ramogida, B. Coppi Considering the effects that plasma disruptions can have, we focus on the Vertical Displacement Events (VDEs) in IGNITOR, the high field compact machine designed for the investigation of fusion burning plasmas at or close to ignition. The stabilization of highly elongated plasma is assured on the fast time scale (tens of ms) by an integrated system designed to control on a slower time scale (hundreds of ms) also the plasma shape and the plasma current. We will discuss two different approaches toward a possible mitigation of the VDEs. The first technique considers the main physical variables related to this instability, limiting the parametric analysis to those variables that can be effectively measured, modeled and controlled with suitable actuators so as to avoid unsafe operation. The second approach consists of the optimization of the equilibrium configurations so as to guarantee better control margins while keeping the main shape constraints. This will be done using the so-called dynamical allocation of the poloidal field coil currents. The aim is to achieve the best possible compromise between keeping the desired plasma equilibrium configuration and using a set of currents far enough from the saturation of the amplifiers. *Sponsored by ENEA of Italy. [Preview Abstract] |
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GP9.00069: Optimal Equilibria and Plasma Parameter Evolutions for the Ignitor Experiment* A. Airoldi, G. Cenacchi, B. Coppi In view of the operation of the Ignitor machine in both the H and the I-regime, optimal equilibrium configurations that can sustain plasma currents $I_p$ up to 10 MA with a double X-point have been identified. In fact, the emergence of the I-regime in double X-point configurations has not been observed experimentally yet. The characteristics of the magnetic equilibrium configurations that can be produced play a crucial role in the performance of the machine. Therefore, particular care has been devoted to the study of plasma equilibria relevant to the main phases of the discharge evolution. A series of simulations to be utilized for the control of the relevant (sub-ignited) plasma parameters has been carried out using the JETTO transport code considering different values of the plasma current and, correspondingly, of the magnetic field. Special attention has been devoted to non-igniting experiments with $I_{p}=5$ MA and $B_{T}=8$ T, where $B_{T}$ is the toroidal magnetic field, as they can be performed with much better duty cycles and longer duration than experiments aimed at reaching the most extreme plasma parameters and ignition in particular. The results of the relevant analyses with a discussion of the adopted transport coefficients is presented. *Sponsored in part by ENEA and the U.S. DOE. [Preview Abstract] |
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GP9.00070: US International Stellarator Collaboration D.A. Gates, M. Bitter, J. Canik, J. Geiger, M. Goto, J.H. Harris, K.W. Hill, S. Lazerson, J. Lore, D. Monticello, Y. Narushima, G.H. Neilson, N. Pablant, N. Pomphrey, A. Reiman, S. Sakakibara, A. Sontag, A. Werner, R. Wolf, G.A. Wurden The US program is using international collaboration to stay at the forefront of experimental stellarator science. The LHD is the premier operating stellarator in the world. The US recently installed an X-ray Imaging Crystal Spectrometer on LHD to aid in the measurement of Ti profiles in difficult plasma regimes - e. g., RF operations, high density, and low density (N. Pablant, this conf.). An effort is underway to develop equilibrium reconstruction for stellarators (S. Lazerson, and A. Sontag this conf.). Results from experiments on the MHD stability of high performance regimes observed on LHD will be presented. The US is also collaborates with W7-X. The collaboration theme on W7-X is divertor heat-flux management. Collaborations on hardware include trim coils, diagnostics (G. Wurden, this conf.), and PFCs (J. Harris, this conf.). Active control that involves real-time equilibrium control and temperature monitoring will be discussed. [Preview Abstract] |
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GP9.00071: First results from the high-resolution x-ray imaging crystal spectrometer on the Large Helical Device N. Pablant, M. Bitter, L. Delgado-Aparicio, K. Hill, S. Lazerson, L. Roquemore, D. Gates, D. Monticello, H. Neilson, A. Reiman, M. Goto, S. Morita, H. Yamada, M. Reinke, J. Rice A high-resolution x-ray imaging crystal spectrometer (XICS) was recently installed on the Large Helical Device for the 2011 experimental campaign. This diagnostic provides profile measurements of ion and electron temperature profiles in LHD with a spatial resolution of $\sim2cm$, a time resolution of $\geq{}10ms$ and coverage from the core to approximately 60\% of the minor radius. This diagnostic can provide ion temperature profiles under conditions where charge exchange recombination spectroscopy (CER) is not possible (high density) or is perturbative to the plasma (low density or frequency heated plasmas). Measurements are by made by using a spherically bent crystal to provide a 1D image of line integrated spectra from helium-like $Ar^{16+}$ emission. Local temperature values can be inferred from these line integrated spectra through tomographic inversion, which utilizes stellarator equilibrium reconstructions provided by the codes \textsc{vmec}, \textsc{stellopt} and \textsc{pies} (S. Lazerson, et al. this conference). This installation is the first application of the XICS diagnostic technique to stellarator geometry. First experimental results are presented. [Preview Abstract] |
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GP9.00072: US Collaboration on the W7-X stellarator G.A. Wurden, D.A. Gates, J.H. Harris, G.H. Neilson, A. Lumsdaine, A. Simakov, M. Zarnstorff The new US-German collaboration on the W7-X stellarator in Greifswald, is in its first year as an ICC project. Los Alamos, Princeton, and Oak Ridge have organized an effort centered on applications of 3D magnetic fields to improve the performance and design of toroidal confinement devices, and to develop the means to control heat flux in a steady state, high beta, 3D, diverted plasmas with reactor relevant parameters. Presently we have three focus areas: providing copper error correction coils to be mounted externally on the W7-X cryostat, developing a scraper element for the divertor, and working control issues under the theme of 3D Diverted Plasmas. The error correction coils must be designed and built on a fast schedule, to meet assembly timelines. ORNL has recently contributed to the design of the support fixtures for the room temperature to cyrogenic coil connections. The LANL effort involves theoretical modeling of whether the stellarator bootstrap current depends on the radial electric field, and an experimental investigation (IR imaging) of the heat loading and wall interactions in the W7-X divertor. W7-X is a modular niobium-titanium superconducting stellarator of the helias type, with 5-fold symmetry. It is presently 4/5 assembled, and first plasma is scheduled for August 2014. Other opportunities for increased collaboration scope abound. [Preview Abstract] |
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GP9.00073: Design of Divertor Scraper Elements for the W7-X Stellarator Jeffrey Harris, Arnold Lumsdaine, John Canik, Jeremy Lore, Dean McGinnis, Alan Peacock, Fred Hurd, Jean Boscary, Joachim Geiger, Joseph Tipton A PPPL/ORNL/LANL team is partnering with the Max-Planck Institut f\"{u}r Plasmaphysik in the Wendelstein 7-X (W7-X) stellarator project. W7-X is a large superconducting, steady-state stellarator (R = 5.5, a = 0.5, B = 3T) with P =15-30 MW that will begin operation in 2015. The US team is focusing on control of the magnetic configuration and divertor heat flux. The W7-X divertor consists of cooled CFC plates arranged as a magnetic island divertor outside the last closed flux surface. While the W7-X configuration is optimized to minimize both Pfirsch-Schl\"{u}ter and bootstrap currents, the $\sim $30 sec evolution of the plasma to its final equilibrium drives bootstrap currents which transiently alter the distribution of divertor heat flux. This necessitates the addition of 10 actively cooled scraper elements (dimensions $\sim $0.2 m x 1 m) capable of absorbing localized heat fluxes $<$ 12 MW/m$^{2}$. ORNL/IPP are developing an engineering design for the scraper elements using ITER CFC monoblock technology. [Preview Abstract] |
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GP9.00074: Linear gyrokinetic studies in NCSX and W7-X stellarators with the GS2 code J.A. Baumgaertel, W. Guttenfelder, G.W. Hammett, D.R. Mikkelsen, P. Xanthopoulos, J. Geiger, W. Dorland, E. Belli The GS2 gyrokinetic code is being used to study microinstabilities and turbulence in non-axisymmetric flux-tube geometries. Non-axisymmetric systems, such as stellarators, have a number of interesting features, like natural reversed magnetic shear and a large number of shaping parameters. These offer possibilities for reducing microturbulence and improving performance. The NCSX and W7-X designs were partially optimized for neoclassical transport; however, the turbulent transport has not been studied in detail. We will present studies of gyrokinetic instabilities in NCSX and W7-X equilibria, including important geometry and linear benchmarks between GS2 and GENE, a gyrokinetic code from IPP. We will also discuss improvements to the GS2 trapped particle treatment and a new computational grid generator for GS2. [Preview Abstract] |
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GP9.00075: Using 3-D shaping to reduce turbulence drive Mordechai Rorvig, Chris Hegna This work explores how the 3-D magnetic field geometry of a stellarator can be modified to reduce the growth rates of turbulence inducing microinstabilities. Ion temperature gradient (ITG) modes are studied. As has been previously noted, minimizing the ``bad curvature'' region has a beneficial effect on ITG stability for turbulence reduction [1]. In this work, we consider how other distinct geometric properties like local magnetic shear can be used to further improve the ITG stability. Sequences of MHD equilibrium surfaces are generated using local 3-D equilibrium theory [2], simplifying the calculations. Instability growth rates for a linear ITG mode [3] are numerically calculated and interpreted.\\[4pt] [1] H. E. Mynick, N. Pomphrey, and P. Xanthopoulos, Physics of Plasmas 18, 056101 (2011).\\[0pt] [2] C. C. Hegna, Physics of Plasmas 7, 3921 (2000).\\[0pt] [3] J. Anderson, T. Rafiq, M. Nadeem, and M. Persson, Physics of Plasmas 9, 1629 (2002). [Preview Abstract] |
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GP9.00076: Exploration of turbulent optimization in toroidal configurations H. Mynick, N. Pomphrey, P. Xanthopoulos We continue exploration of the potential for reducing the levels of turbulent transport in stellarators and tokamaks, making use of the STELLOPT optimization code and the GENE gyrokinetic code. The original applications of the method focused on ion temperature gradient transport in a quasi-axisymmetric stellarator design.\footnote{H.E. Mynick, N. Pomphrey, P. Xanthopoulos, Phys. Rev. Letters, 105, 095004 (2010).} The method has now been applied to both other starting configurations, including tokamaks and other stellarator classes, and to other turbulence channels.\footnote{H.E. Mynick, N. Pomphrey, P. Xanthopoulos, Phys. Plasmas, 18, 056101 (2011).} This growing body of results is finding that the effectiveness of the current proxy measure Q$_{prox}$ used by STELLOPT to estimate transport levels differs depending on the class of toroidal device considered. Also, the dependence of Q$_{prox}$ on the radial curvature captures well what GENE simulations find$^{2}$, but its dependence on local shear needs refinement for this very important ``knob'' to also be used in the turbulent optimization. We are using these results to discern the different physics features causing this, and thereby to improve Q$_{prox}$. [Preview Abstract] |
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GP9.00077: Mapping the global topography of the cost function in STELLOPT M. Lucia, H.E. Mynick, N. Pomphrey Stellarator designs have long been optimized for reduced neoclassical transport, but optimization for reduced turbulent transport is a relatively nascent research thrust. Recent work has addressed\footnote{H.E. Mynick, N. Pomphrey, P. Xanthopoulos, PRL $\textbf {105}$, 095044 (2010)} this ``turbulent optimization'' by using the GENE/GIST nonlinear gyrokinetic code and the STELLOPT stellarator optimization code. That work demonstrated that STELLOPT can produce stellarator designs that reduce the turbulent transport without adversely affecting other design metrics. STELLOPT utilizes a Levenberg-Marquardt (LM) algorithm to find a local minimum of a cost function in a shape space $\textbf{z}$ of coefficients that define the plasma boundary. However, a visualization of the topography of the cost function in $\textbf{z}$ space might reveal a lower global minimum and provide insight into why the LM algorithm missed it. The current work uses STELLOPT to provide this capability, replacing its LM algorithm with one that produces maps of the wider topography of the cost function. Analysis of these maps will be used to gain insight into the properties of the studied design configurations and to identify possible improvements to STELLOPT's optimization algorithm. [Preview Abstract] |
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GP9.00078: Experimental Study of MHD mode rotation in the Edge Plasmas of the Large Helical Device Y. Takemura, S. Sakakibara, K.Y. Watanabe, K. Ida, S. Ohdachi, Y. Suzuki, Y. Narushima, I. Yamada, K. Narihara, K. Tanaka, T. Tokuzawa, H. Yamada The relationship between MHD mode rotation and the plasma flow has been investigated on Large Helical Device (LHD). Several MHD modes excited in edge region of plasma have been dominantly observed in high-beta regime. Especially, the modes in the stochastic layer are key instabilities for degradation of high beta plasma and/or the formation of the edge transport barrier. In order to understand the mechanism of MHD mode rotation, the electron density scan experiment was performed to widely change the radial electric field and poloidal flow. Experiments indicate the following results: MHD modes rotate in the electron diamagnetic direction with several kHz in the laboratory frame and the frequencies gradually decrease with the density. Poloidal plasma flow is dominant at objective resonances because toroidal flow is almost zero there. With respect to modes inside last closed flux surface (LCFS), the mode frequency in the plasma frame is quantitatively consistent with the electron diamagnetic drift frequency within the measurement error, which means that the observed modes rotate with the electron fluid. The frequency of the mode outside LCFS seems to be much closer to the ion diamagnetic drift frequency than to the electron one. [Preview Abstract] |
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GP9.00079: Behavior of poloidal rotation during transition of magnetic island dynamics in LHD Y. Narushima, F. Castej\'on, S. Sakakibara, K.Y. Watanabe, M. Yoshinuma, H. Funaba, S. Ohdachi, Y. Suzuki, S. Nishimura, C.C. Hegna, T. Estrada, F. Medina, D. Lopez-Bruna, M. Yokoyama, K. Ida In the LHD experiments, the growth or disappearance of the $n$ = 1 magnetic island during a discharge has been observed. Generally, at low $\beta $ and high $\nu $, the plasma tends to make the island grow in width. However at sufficiently high $\beta $ and/or low $\nu $, the islands are suppressed. In TJ-II, large islands are suppressed or prevented to appear due to the positive electric fields created by the rational itself. Those ingredients point to the island dynamics be related to the poloidal rotation, which changes prior to the magnetic island transition. Thresholds of the poloidal rotation for each transition are different. The poloidal rotation for island suppression is smaller than that for island growth. The experimental result shows the existence of a hysteresis in the magnetic island transition dynamics. This result is consistent with a theoretical model based on the balance of electromagnetic and viscous torques at the rational surface. [Preview Abstract] |
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GP9.00080: Simulation of heat transport in LHD plasmas using the integrated code: TASK3D A. Wakasa, A. Fukuyama, S. Murakami, M. Yokoyama, M. Sato, S. Toda, H. Funaba, R. Seki, K. Tanaka, K. Ida, H. Yamada, N. Nakajima An integrated transport simulation code for helical plasmas, TASK3D, has been developed and applied to the LHD plasmas. The neoclassical transport in LHD plasma is evaluated by the neoclassical transport database module, DGN/LHD, using a neural network technique. The radial electric field module, ER, which solves the differential equation of the radial electric field has been also developed. In this study, the behavior of the LHD plasmas is simulated with several anomalous transport models and the temperature profiles are compared with experimental observations. Reasonable agreements of the radial electric field profile between simulation results and the experimental ones are obtained by use of the ER module. It is found that the anomalous transport dominates in the electron heat transport, while the neoclassical transport plays a crucial role in the ion heat transport. [Preview Abstract] |
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GP9.00081: Asymptotic expansion for stellarator equilibria with a non-planar magnetic axis Antoine Cerfon, Felix Parra, Jeffrey Freidberg We perform an asymptotic analysis to reduce the complexity of the MHD equilibrium equations in stellarators. In our new formulation, stellarator equilibria are fully determined by the solution of a set of two simple looking coupled partial differential equations for the plasma pressure and the magnetic vector potential. As in the classic work by Greene and Johnson [1], the asymptotic expansion relies on the ratio of the helical magnetic field to the vacuum toroidal field. However, our ordering for the equilibrium quantities generalizes that of [1] in order to provide a better match with modern stellarator experiments. In particular, toroidal effects enter the analysis in the same order as helical effects, allowing the calculation of equilibria with multiple helicities and a non-planar magnetic axis. To illustrate the simplicity and the versatility of our approach, we construct semi-analytic solutions to the system of equations for the pressure and the vector potential. With these solutions, we compute stellarator equilibria for several special cases. \\[4pt] [1] J.M. Greene and J.L. Johnson, Phys. Fluids 4, 875 (1961) [Preview Abstract] |
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GP9.00082: Equilibrium, stability and transport in quasi-symmetric stellarators A.S. Ware, F. Bunt, K. Lennard, T. Marine, K. McGarvey-Lechable We present an overview of research efforts at the University of Montana to understand the equilibrium, stability and transport properties of quasi-symmetric stellarators. Quasi-symmetry in three-dimensional magnetic confinement devices provides a path for external control of the confining magnetic field while achieving confinement comparable to axisymmetric configurations. In a quasi-symmetric toroidal configuration, magnetic field strength in magnetic flux coordinates is given by $B\left( \psi, \theta, \zeta \right) \approx B\left( \psi, M\theta + N\zeta \right)$ where $M$ and $N$ are integers. We summarize efforts to optimize quasi-symmetric configurations, both fixed- boundary and free-boundary. The ideal ballooning stability properties of these configurations are analyzed and finite-$\beta$ optimizations are undertaken to improve stability. Transport properties are analyzed using the NEO and PENTA codes and the effect of symmetry-breaking has been tested. Finally, an effort to develop a transformation from Boozer coordinates to VMEC coordinates is discussed. [Preview Abstract] |
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GP9.00083: Effect of superbanana diffusion on the fusion reactivity in QHS stellarators Fred Hinton The effect of superbanana diffusion on the D-T fusion reactivity in QHS (quasi-helically-symmetric) stellarators has been investigated. The fusion reactivity was expected to be significantly reduced because of the strong energy-dependence of the diffusion coefficient in the ``1/nu regime.'' However, several mitigating effects make this effect weaker: (1) with realistic density and temperature profiles, the reaction rate peaks in the plasma core, while the diffusion is largest near the edge, where the helical magnetic field ripple is strongest; (2) the poloidal precession rate may be larger when the ambipolar electric field is included, which would reduce the superbanana orbit width and bring the transition to the ``nu regime'' down to lower energies. The Fokker-Planck equation has been solved numerically, including superbanana diffusion as well as energy scattering, to obtain the energy dependence for the tail of the ion distribution function. A previous calculation used separation of variables, assuming uniform ion temperature and electrostatic potential, to obtain a steady-state solution. It was found that, even for very small values of the effective helical field ripple, the fusion reactivity was significantly reduced. The calculation reported on here uses an initial-value formulation to obtain a steady state solution without assuming the ion temperature or electrostatic potential to be uniform. A smaller reduction of the fusion reactivity due to superbanana diffusion has been found. [Preview Abstract] |
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GP9.00084: Alfv\'{e}n instabilities and energetic particle physics in stellarators Don Spong Stellarators, helical RFPs and 3D tokamaks introduce symmetry-breaking effects that alter the structure of Alfv\'{e}n instabilities and their impact on energetic particle confinement. Loss of symmetry precludes an ignorable coordinate and requires taking into account both poloidal and toroidal couplings. New techniques for near term progress in 3D EP modeling have been developed, such as scalable algorithms (e.g., perturbative particle methods and windowed frequency solvers) and reduced-dimensionality models (e.g., gyro-Landau fluid). These methods have been developed for a range of 3D (tokamak/stellarator/RFP) configurations and have been compared with experimental measurements on LHD, TJ-II, HSX and RFX. Both modes with weak 3D couplings (TAE's in LHD) and strong 3D couplings (HAE's in TJ-II) will be discussed. Also, code-benchmarking activities have been started and will be described. In addition to their impact on fast ion confinement, the coherent frequencies of these AE modes (directly related to iota) can be useful markers for 3D equilibrium reconstruction. [Preview Abstract] |
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GP9.00085: Simulation Study of Energetic Particle Driven Geodesic Acoustic Mode in LHD Plasma Hao Wang, Yasushi Todo The energetic particle driven geodesic acoustic modes (GAMs) in LHD plasma were simulated using a hybrid simulation code for magnetohydrodynamics (MHD) and energetic particles. The energetic particle distribution employed in the simulation is anisotropic in velocity space. The GAM frequencies in the simulation results are 38kHz for 5.0keV electron temperature and 20kHz for 1.3keV electron temperature. The frequencies agree reasonably with both the experimental observation and the prediction from MHD theory. The poloidal velocity $v_\theta$ with mode number m=0 and perturbed pressure \~{P} and density \~{n} with mode number m=1 are observed. The GAM is excited around the normalized minor radius 0.2, and it propagates in radial direction. In addition, the spatial profiles of \~{P} and \~{n} rotate in poloidal direction. After the saturation of the instability, redistribution of energetic particles takes place in pitch-angle space both for the lower pitch-angle part and for the higher pitch-angel part. [Preview Abstract] |
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GP9.00086: Nonlinear collision effect on $\alpha$-particle confinement in toroidal plasmas Yoshitada Masaoka, Sadayoshi Murakami In helical systems, high-energy particle trajectory is complicated in a three dimensional magnetic configuration and, thus the confinement of alpha particles is one of the critical issues in designing helical reactor. In addition to that, circulating fast ions affect the cross section of the first ion itself. Thus the analysis including the both complicated orbit and nonlinear collision effects are necessary to make clear the $\alpha$-particle confinement in heliotropes. In this paper, we study the $\alpha$-particle confinement including the collision with various plasma species such as electron, deuterium, tritium, and high-energy $\alpha$-particle. We improve the GNET code to take into account the nonlinear collision effect in a heliotrope fusion reactor based on the LHD configuration. We analyze the real and velocity space distributions and the energy and particle loss fraction changing the background plasma parameters, and verify the effects of collision between high-energy particles on the alpha-particle confinement. [Preview Abstract] |
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GP9.00087: Finite beta stellarator simulations using NIMROD M. Schlutt, C.C. Hegna, C.R. Sovinec, E. Held, S.E. Kruger, J. Hebert In the first class of calculations shown, a vacuum equilibrium helical magnetic field is loaded into the geometry of a straight stellarator. The vacuum magnetic field is initialized to be symmetric or to have spoiled symmetry by adding 3D magnetic perturbations with helicities that are incommensurate with the dominant harmonic. These perturbations alter the magnetic spectrum, and create magnetic islands and regions of stochasticity. Finite beta equilibria are generated by introducing a heating source and employing self-consistent anisotropic transport. The connection between high beta properties of systems with saturated instabilities and equilibrium beta limits are discussed. The second set of calculations shown is motivated by recent results from LHD and includes a locked magnetic island in vacuum. A poloidal momentum source is added inboard of the island, creating a viscous drag on the island region. The phase of the locked island changes as the flow increases, and the island spontaneously disappears when the flow becomes high enough. In the third case presented, the Compact Toroidal Hybrid (CTH) is modeled. The vacuum field is loaded and a loop voltage is applied creating finite beta configurations. [Preview Abstract] |
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GP9.00088: NIMROD Simulations of CTH Non-Axisymmetric Plasmas Jonathan Hebert, Mark Schlutt The NIMROD code has recently been modified to allow for simulations of non-axisymmetric plasmas. As an early application of this new method, stellarator-like fields in the Compact Toroidal Hybrid (CTH) at Auburn University have been simulated and analyzed. A comparison between NIMROD calculated equilibrium fields and modeled equilibrium fields is presented. Also, plans for a study of disruptions caused by edge magnetic islands in the CTH are presented. [Preview Abstract] |
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GP9.00089: 3D Equilibrium Reconstruction in Action: V3FIT J.D. Hanson, G.J. Hartwell, S.F. Knowlton, B.A. Stevenson, S.P. Hirshman, A.C. Sontag, J.C. Schmitt, D. Terranova The 3D equilibrium reconstruction code V3FIT [1] is in routine use on stellarator experiments (CTH, HSX). It is in preliminary use on LHD and the Reversed Field Pinch RFX (Padova). Recent developments to the code include the ability to reconstruct using fixed boundary equilibria, addition of a mechanism for using compensated diamagnetic loops as signals, an improved mechanism for using soft x-rays as signals, an improved specification of limiters, and the ability to apply arbitrary shifts and rotations to external coils. The coordination between V3FIT and the underlying VMEC2000 [2] code (the 3D equilibrium code which V3FIT uses) has been improved, leading to more robust reconstructions. Results from various machines along with plans for future improvements in the code will be presented. \\[4pt] [1] J. D. Hanson, S. P Hirshman, S. F. Knowlton, L. L. Lao, E. A. Lazarus, and J. M. Shields, Nucl. Fusion \textbf{49}, 075031 (2009).\\[0pt] [2] S. P. Hirshman and J. C. Whitson, Phys. Fluids \textbf{26}, 3553 (1983). [Preview Abstract] |
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GP9.00090: Equilibrium Reconstruction of LHD Discharges using V3FIT Aaron Sontag, J. Hanson, J. Harris, S. Ohdachi, S. Sakakibara, Y. Suzuki The presence of significant pressure driven currents as well as the ability to drive tens of kiloamperes of toroidal plasma current in LHD leads to deviations in the equilibrium magnetic geometry from the vacuum flux surfaces. The V3FIT code is being used to reconstruct non-axisymmetric stellarator equilibria for LHD discharges with the assumption of good flux surfaces. The present work is a study of the ability of the V3FIT code to reliably reconstruct the plasma equilibrium state for a variety of LHD discharge types using the existing diagnostics. The initial diagnostic set studied consists of the measured coil currents, the total plasma current, magnetic diagnostics and soft x-ray diode arrays. The accuracy of the reconstructed current and pressure profiles using this initial diagnostic set is assessed and the relative effectiveness of each diagnostic is determined for each fit parameter. [Preview Abstract] |
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GP9.00091: Disruptions and disruption avoidance in the CTH torsatron/tokamak experiment S.F. Knowlton, G.J. Hartwell, J.D. Hanson, J.L. Herfindal, M.C. Miller, B.A. Stevenson It has long been known that disruptions are rare in current-carrying toroidal plasmas if the discharge is performed within a stellarator equilibrium with a modest vacuum rotational transform of $\iota \quad \le $ 0.14 [1]. Experiments are performed in the current-carrying Compact Toroidal Hybrid (CTH) torsatron/tokamak (R = 0.75 m, a $\sim $ 0.2 m, B $\le $ 0.7 T, I$_{p} \quad \le $ 65 kA, n$_{e} \quad \le $ 10$^{19}$ m$^{-3})$ to better understand the conditions for passive disruption. As in previous experiments, we find that disruptions characterized by a rapid current quench do not occur if the applied vacuum rotational transform $\iota _{VAC}$(a) exceeds a value of $\sim $0.15 even though stable plasmas with q$_{edge}$ of 1.6 are obtained. Below this threshold transform, disruptions can be triggered by ramping the plasma density to levels comparable to the Greenwald density limit. These and other disruptions also arise from a vertical instability in which the plasma channel drifts upward. The vertical instability is reduced or eliminated with (1) sufficient external transform, or (2) reduction of the vertical elongation using a pair of quadrupole shaping coils. \\[4pt] [1] W VII-A Team, Nucl. Fusion \textbf{20} 1093 (1980) [Preview Abstract] |
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GP9.00092: Equilibrium Reconstruction using Soft X-Ray Chordal Diagnostics on the Compact Toroidal Hybrid Experiment G.J. Hartwell, J.D. Hanson, J.L. Herfindal, S.F. Knowlton, M.C. Miller, B.A. Stevenson Equilibrium reconstructions using the V3FIT [1] code will be presented for current carrying plasmas on the Compact Toroidal Hybrid (CTH) torsatron experiment (R = 0.75 m, a $\sim $ 0.2 m, B $\le $ 0.7 T, ne $\le $ 10$^{19}$ m$^{-3}$, Te $\le $ 250 eV). The reconstruction input data set includes the Soft X-Ray (SXR) chord signals normally used for tomographic reconstructions. Four cameras, each consisting of a 20-channel AXUV-20EL photo-diode array view the CTH plasma through 2$\mu $m Be foil. Three cameras view the plasma at one symmetry plane ($\varphi $ =36$^{\circ})$ while the fourth views the plasma at another symmetry plane ($\varphi $ =0$^{\circ})$, one-half field period away. When observed, sawtoothing provides additional constraints to reconstructions. The reconstructions assume uniform SXR emissivity on a flux surface. The SXR signals provide additional data inputs to V3FIT, which has primarily used magnetic data to fit the equilibrium. \\[4pt] [1] J. Hanson, S. Hirshman, S. Knowlton, L. Lao, E. Lazarus, J. Shields, Nucl. Fusion, \textbf{49} (2009) 075031 [Preview Abstract] |
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GP9.00093: Reconstruction of Plasma Equilibria Using Magnetic Diagnostics on the Compact Toroidal Hybrid B.A. Stevenson, J.D. Hanson, G.H. Hartwell, S.F. Knowlton The ability to reconstruct fully three-dimensional plasma equilibria is becoming increasing important in today's fusion energy experiments. Reconstructions of plasma equilibria in the Compact Toroidal Hybrid (CTH) using magnetic diagnostics and the V3FIT equilibrium reconstruction code [1] will be presented. The CTH is a heliotron-type device in which the magnetic configuration can be strongly modified by an ohmically-driven plasma current. Equilibria on CTH are reconstructed using signals from segmented and full Rogowski coils which provide the experimental input used within V3FIT. Significant reductions in systematic errors have resulted in more consistent reconstruction results. Many of the remaining differences between the reconstructed and experimental signals have been shown to be time dependent. The time evolution of the reconstructed current density profile for a series of plasma conditions will be presented. An array of Hall probes is used to measure the poloidal magnetic field within the plasma. These direct magnetic field measurements have been compared to those calculated from the reconstructed plasma.\\[4pt] [1] J. D. Hanson et al, Nucl. Fusion 49, 075031 (2009) [Preview Abstract] |
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GP9.00094: X-Ray Observations and Electron Temperature Measurement by Soft X-Ray Spectroscopy on the CTH Experiment J.L. Herfindal, G.J. Hartwell, S.F. Knowlton Hard x-ray (HXR) emission of runaway electrons with energies up to a few MeV are observed in the Compact Toroidal Hybrid (CTH) torsatron experiment ($R = 0.75m$, $a \sim 0.2m$, $B \leq 0.7~T$, $n_e \leq 10^{19}~m^{-3}$, $I_p \leq 65~kA$). HXRs were measured using a scintillator approximately $4m$ from the CTH device oriented tangentially to the plasma current. A sudden absence of HXRs before and during abruptions in the plasma current was observed. Electron temperature measurements are derived from soft x-ray measurements using an Amptek spectrometer. The soft x-ray spectrometer views the Bremsstrahlung emission along a single chord through the plasma in the energy range from $0.7 - 4 keV$. Central temperature measurements will be presented. [Preview Abstract] |
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GP9.00095: A Microwave Interferometer for Density Measurements on CTH M.C. Miller, J.-T. Chen, G.J. Hartwell, S.F. Knowlton, B.A. Stevenson Most plasma physics research experiments rely heavily on plasma density measurements; requiring these diagnostics to be reliable, easily maintained, and relatively inexpensive. On the Compact Toroidal Hybrid experiment (CTH), disruptions can be triggered by high density excursions, which are often associated with a vertical displacement. The existing horizontally viewing $4\mathrm{\,mm}$ wave system loses the ability to count fringes at those high densities and vertical offsets. A new three channel $1\mathrm{\,mm}$ wave Michelson interferometer for use on CTH has been designed, assembled, and tested. Several design features lend to reliability and maintainability. The interferometer employs a single electronically tunable source that is repetitively chirped to provide heterodyne detection. A drive oscillator operates at $15.25\mathrm{\,GHz}$ and is multiplied through two stages up to 122 GHz before a final doubler stage brings it to $244\mathrm{\,GHz}$. The local oscillator at $122\mathrm{\,GHz}$ is fed into a subharmonic mixer for each viewing cord. The lower frequency of the reference beam allows wave guide to be used with low loss and greatly reduces alignment difficulty. Phase detection is performed digitally. An overview of the design and preliminary data will be presented. [Preview Abstract] |
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GP9.00096: Measurements and Simulations of Electric Field Modified Flows in the Compact Toroidal Hybrid Stellarator Mark Cianciosa, Greg Hartwell, Jim Hanson, Stephen Knowlton, Edward Thomas Sheared flows arising from spatially inhomogeneous, transverse electric fields are common phenomena found in space, laboratory, and fusion plasmas. These flows are a source of free energy that can drive or suppress instabilities. In fusion plasmas, edge localized sheared flows provide a barrier against cross field particle transport and the presence of these flows are associated with enhanced confinement regimes (H-mode). The Compact Toroidal Hybrid (CTH) is five field period continuously wound stellarator ($R_{0}=0.75m$, $a\sim0.2m$, $B_{0}\le0.7T$, $\bar{n}_{e}=0.2- 1.5\times10^{19}m^{-3}$) run with $100ms$ long plasmas. Primary plasma generation and heating is provided through Electron Cyclotron Resonance Heating (ECRH) with a secondary Ohmic heating system. Flow experiments are performed by modifying the radial electric field by inserting an biasing electrode probe past the last closed flux surface. Plasma parameters are measured using a triple probe. Initial measurements of flows from a newly constructed Gundestrup probe will be presented. This presentation will also discuss the interpretation of probe measurements in a flux coordinate system. [Preview Abstract] |
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GP9.00097: Modeling the radial electric field and comparison with HIBP measurements in TJ-II stellarator Cesar Gutierrez-Tapia, Julio J. Martinell, Daniel Lopez-Bruna, Alexander Melnikov Neoclassical transport calculations from three different models representing regimes with a wide variation of collisionality are used for estimating the radial electric field in the TJ-II stellarator and the results of are compared with measurements by Heavy Ion Beam Probe (HIBP). In particular we also use a simplified model that considers only the non-axisymmetric contribution to the transport, due to Kovrizhnykh [1], to perform analytical calculations for given density and temperature profiles taken from experiment. These encompass a wide range of densities corresponding to ECH and NBI regimes. Quite satisfactory agreement between modeling and experimental data is shown fro both the numerical models and the analytical calculations, for all regimes thus allowing to conclude that the neoclassical transport is the main contributor to the formation of the radial electric field in TJ-II. The analytical approach permits a good understanding about the conditions that have to satisfy the steady states in order to obtain real roots for the radial electric field over all the plasma cross section, that in addition are in agreement with experimental HIBP measurements. \\[4pt] [1] L.M. Kovrizhnykh, Plasma Phys. Rep. {\bf 31}, 14 (2005) [Preview Abstract] |
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GP9.00098: Recent Results and New Directions of the HSX Program D.T. Anderson, F.S.B. Anderson, A.R. Breisemeister, E. Chlechowitz, C. Clark, C. Cook, L. Hurd, K.M. Likin, J. Radder, J.C. Schmitt, L. Stephey, J.N. Talmadge, G. Weir, R. Wilcox, K. Zhai, D. Brower, C. Deng Intrinsic rotation velocities of up to 20 km/s in the symmetry direction have been measured with the ChERS system and compared to the PENTA code. Flow velocity increases with increasing ECH power while density fluctuations and frequency on the interferometer decrease. The second ECH source is now operational. Reflectometry is now being used to measure density fluctuations and being upgraded to a Doppler system. Reynolds stress calculations are made using probe data. ECH distribution function modifications are calculated with the GNET code and used to help model ECE. Laser blow-off experiments have begun for impurity transport. Particle transport at B=1T is being studied with expanded H-alpha arrays and DEGAS2. SIESTA is being modified to handle more diverse forms of equilibria. The edge field structure in HSX is being re-examined for potential new divertor studies. Magnetics diagnostics show a helical Pfirsch-Schluter current and used for V3FIT reconstruction. Studies are underway to optimize design of magnetic diagnostics for improved reconstruction. [Preview Abstract] |
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GP9.00099: Measuring and Predicting the Flow Velocity in the HSX Stellarator A. Briesemeister, K. Zhai, J. Radder, D.T. Anderson, F.S.B. Anderson, J.N. Talmadge Charge exchange recombination spectroscopy is used to measure the ion flow in HSX. The flow velocity measured at several radial locations increases when the electron temperature and temperature gradient are increased by increasing the electron cyclotron resonance heating power or changing the deposition location. Similar increases are predicted in the neoclassical radial electric field and the net parallel flow velocity profiles calculated using the PENTA code [1]. In order to quantitatively compare the calculated and measured values, a synthetic diagnostic has been developed to calculate the relationship between the neoclassically predicted values, the fully 3D flow (including the Pfirsch-Schl\"{u}ter velocity) and the measured flows. A comparison between the ECRH driven electron flux calculated using the GNET code [2] and the neoclassical flux will be presented to show the effects this flux will have on the predicted radial electric field. \\[4pt] [1] J. Lore et al, Phys. Plasma 17 (2010) 056101.\\[0pt] [2] Murakami et al, Nucl. Fusion 40 (2000) 6930. [Preview Abstract] |
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GP9.00100: Core Density Fluctuation Measurements by Interferometry in the HSX Stellarator C. Deng, D.L. Brower, D.T. Anderson, F.S.B. Anderson, A. Briesemeister, K. Likin, J.C. Schmitt, J.N. Talmadge, R. Wilcox, K. Zhai The multichannel interferometer system on the HSX stellarator is optimized to measure electron density fluctuations by utilizing both phase and amplitude techniques Information on core and edge fluctuations can be realized by comparing chords at different locations or by use of the differential interferometry approach. Both coherent modes and broadband density fluctuations with frequency up to 250 kHz are measured. For quasi-helically symmetric plasmas with B$_{T}$=1.0 T, significant changes (both amplitude and frequency) in the turbulent density fluctuation spectrum are observed when heating location changes from on-axis to high field side. Density fluctuation amplitude and frequency decrease with increasing of ECRH power ($\sim $T$_{e})$. Changes in fluctuations will be compared with measurements of plasma flow (by CHERS) as well as electron density and temperature profile modifications. When HSX is operated without quasi-helical symmetry at B$_{T}$=1T and n$_{e}\sim $4x10$^{12}$ cm$^{-3}$, a coherent electrostatic mode at $\sim $28 kHz is observed. Fluctuation sensitivity to changes of heating location and ECRH power were not observed for these plasmas. [Preview Abstract] |
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GP9.00101: Laser Blow-Off Impurity Injection Experiments at the HSX Stellarator C. Clark, D.T. Anderson, F.S.B. Anderson, K.M. Likin, J.N. Talmadge, K. Zhai, J. Lore Experiments are under way to measure impurity transport in a quasisymmetric stellarator for the first time. A laser blow-off impurity injection system, which is capable of rapidly depositing a small, controlled quantity of a wide variety of solid impurities into the confinement volume, has been installed and successfully tested. AXUV photodiode arrays equipped with optional soft x-ray filters have also been installed on the machine. The arrays will take time-resolved measurements of the impurity radiation, which will be inverted into radial profile and then interpreted using the transport code, STRAHL and atomic data from ADAS to determine the transport coefficients within the paradigm of a diffusivity and convective velocity. Details of the system and first results will be presented along with PENTA calculations of the neoclassical predicted impurity transport [Preview Abstract] |
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GP9.00102: Neutral Particle Studies in the HSX Stellarator L. Stephey, A. Briesemeister, D.T. Anderson, J.N. Talmadge, F.S.B. Anderson Previously in the HSX stellarator, fully 3-D DEGAS [1] simulations at B=0.5 T operation have calculated neutral profiles for several plasma configurations [2]. DEGAS 2 [3] will be used to calculate fully 3-D neutral particle profiles for B=1.0 T plasmas. DEGAS 2 calculations presented will use data from an array of absolutely calibrated H-alpha detectors currently installed on HSX. The H-alpha system is being upgraded to provide better resolution of the poloidal distribution of neutrals. The results from DEGAS 2 and the upgraded H-alpha system will be used to help understand differences in plasma behavior as a result of fueling location relative to heating location. B=1.0 T particle flux calculations will be presented in both the quasi-symmetric configuration and when symmetry is intentionally degraded to simulate a conventional stellarator. These results will be compared to neoclassical calculations. *Supported by DOE grant DE-FG02-93ER54222.\\[4pt] [1] D. Heifetz et al., J. Comp. Phys. 46, 309 (1982).\\[0pt] [2] J.M. Canik et al., Phys. Plasmas 14, 056107 (2007).\\[0pt] [3] D.P. Stotler et al., J. Nucl. Mater. 967, 290--293 (2001). [Preview Abstract] |
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GP9.00103: Optimized Design of Magnetic Diagnostics for Improved Equilibrium Reconstruction on the HSX Stellarator E. Chlechowitz, J.C. Schmitt, J.N. Talmadge, D.T. Anderson Measuring the plasma current and pressure profile are essential for determining the equilibrium magnetic field configuration of tokamaks as well as stellarators. HSX equilibria have been reconstructed using a three dimensional equilibrium reconstruction code, V3FIT [1], and a limited set of magnetic pick-up coils [2]. Reconstruction can be improved through an upgrade of the pick-up coil set, providing more discrimination between possible equilibrium solutions. For a set of possible equilibria, described by the parameter set $P$, the signal responses of virtual diagnostics $V_S$ are calculated. The reconstruction is performed by using $V_S$ and $P + \delta P$, with $\delta P$ as deviations, as initial conditions. A code has been written to minimize the error in reconstruction by optimizing the placement of the coil set using the method of steepest descent. Due to the large dimensionality of the problem the code is being run on grid computing. \\[4pt] [1] J.D. Hanson et al 2009 Nucl. Fusion 49 075031 \newline [2] J.C. Schmitt, Invited talk this conference [Preview Abstract] |
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GP9.00104: Initial Operation of the Second ECRH System on the HSX Stellarator G.M. Weir, K.M. Likin, F.S.B. Anderson, D.T. Anderson, J.W. Radder, J.N. Talmadge A second 200 kW / 28 GHz ECRH system has been installed and tested on the HSX stellarator. The Varian gyrotron VGA-8050M has a multimode output that is dominated by the TE02 mode. The gyrotron was tuned to produce a TEM00 mode with Gaussian distribution at the output of the Vlasov mode converter. The beam pattern and transmission line alignment were measured by observing the temperature increase of a target plate at several locations along the beam line with an infrared camera. Power measurements were made at the input and output of the transmission line, and pulsed power experiments into a target plasma show an increase in stored energy commensurate with previous high power experiments using only a single source. The antenna has a steerable focusing mirror within the HSX vessel that allows power deposition studies, specifically the effect of power deposition on ITB formation in the stellarator. This source can also be modulated for heat pulse propagation experiments. [Preview Abstract] |
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GP9.00105: Measurement of Reynolds stress using Langmuir probes in the HSX stellarator R.S. Wilcox, J.A. Alonso, D. Carralero, D.T. Anderson, J.N. Talmadge, F.S.B. Anderson A compact Langmuir probe configuration has been designed and implemented in the edge of plasmas in the HSX stellarator to measure the Reynolds stress contribution to the momentum balance in multiple directions. Measurements are made of the fluctuating values of the radial and poloidal electric field, simultaneously with mach probe measurements of fluctuating values of the parallel flow. Experiments are performed in plasmas with an external bias applied as well as in the unbiased equilibrium case to study the effect of a large radial electric field on the fluctuations. The effect of quasi-helical symmetry on fluctuation-driven flows is also investigated by comparing measurements in an optimized magnetic configuration (QHS) to those in a configuration which has the optimization intentionally degraded (Mirror). [Preview Abstract] |
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GP9.00106: Frequency spectra of plasma density fluctuations in HSX Konstantin Likin, David Anderson, Simon Anderson, Chuanbao Deng, Joseph Talmadge A conventional reflectometer is used to measure plasma density fluctuations in the HSX stellarator. Two sources with a fast switch allow us to sweep the probing beam frequency in the bandwidth of (14.5 - 26.5) GHz that corresponds to the wave reflection into the plasma core. In experiments at 0.5 T a low-frequency coherent mode was detected in the quasi-symmetric configuration. In high density plasmas at 1 T we do not see this mode, while the electron temperature is found to be highly peaked in the plasma core. The ITB formation may be due to suppression of density fluctuations by the radial electric field shear. A comparison of the reflectometer data in various regimes shows little difference in the frequency spectra between plasmas with and without the ITB. Results of the modeling on density fluctuations from the reflectometer data will be discussed. The reflectometer is being upgraded to a Doppler version to provide information on plasma rotation than can be compared with CXRS measurements. The design of the Doppler reflectometer will also be presented. [Preview Abstract] |
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GP9.00107: Modeling of X-Ray Bremsstrahlung and ECE Diagnostics with Non-Maxwellian Electron Distribution Functions in the HSX Stellarator J.W. Radder, K.M. Likin, J.N. Talmadge, D.T. Anderson, G.M. Weir The five-dimensional Fokker-Planck code, GNET [1], is used to model the electron distribution function for electron cyclotron heating (ECH) in the HSX stellarator. GNET solves a linearized drift kinetic equation in three-dimensional magnetic geometry, allowing simulation of HSX magnetic configurations with and without quasihelical symmetry. A routine was developed to calculate X-ray bremsstrahlung radiation spectra with electron distribution functions calculated with GNET. For non-Maxwellian distributions in HSX plasmas, the radiation transport equation is solved to find ECE spectra. Numerical simulations predict hotter plasma temperatures in QHS than Mirror modes, which is attributed to improved confinement of high energy particles in a quasisymmetric magnetic geometry. Comparisons will be made to ECE and X-ray spectra measurements for 2nd-harmonic X-mode (0.5 Tesla) and 1st-harmonic O-mode (1.0 Tesla) plasmas. \\[4pt] [1] S. Murakami, et al, Nuclear Fusion, v. 40, n. 3Y, pp.693-700, 2000. [Preview Abstract] |
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GP9.00108: Using field line following to investigate magnetic island effects on connection length for HSX L.D. Hurd, C.C. Hegna, C. Clark, D.T. Anderson, J.N. Talmadge The divertor configurations in stellarators currently being explored are based on the inherent edge magnetic structures accessible in each particular device. In general, a larger connection length will lead to an enhancement of the perpendicular-to-parallel particle and energy transport in the scrape-off layer. Field line following is used to analyze the effects of varying the magnetic field configurations on connection lengths and strike points for HSX. In particular, the role of n/m = 8/7 and 4/4 magnetic island structures in the edge regions of configurations available to HSX are investigated. Implications for divertor-related studies on HSX will be discussed. [Preview Abstract] |
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GP9.00109: ICF AND HED PLASMAS, SIMULATIONS, HYDRO INSTABILITY |
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GP9.00110: Experimental X-ray Spectra from Ti, V, Mn, and Ni Foils Irradiated with the Z-Beamlet Laser E.C. Harding, T. Ao, J.E. Bailey, S.B. Hansen, M.P. Desjarlais, L.P. Mix, P.D. LePell, D.F. Wenger, I.C. Smith, D.B. Sinars, G. Gregori We present results from our first experimental campaign aimed at investigating various x-ray spectral lines for use in future x-ray Thomson scattering experiments. The Z-Beamlet laser was used to irradiate 4 different metal foils (Ti,V,Mn, and Ni) with 10$^{15}$ W/cm$^{2}$ and a total of 1 kJ at $\lambda $ = 527 nm. The x-rays from the laser-heated plume were observed simultaneously at 90\r{ } and 8\r{ } (w.r.t. the surface) with two time integrating, spatially resolving spectrometers that employed spherical quartz crystals and image plate detectors. The following spectral lines were recorded with E/$\delta $E $\sim $ 1000: Ti He-$\beta $, V He-$\beta $, Mn He-$\alpha $, and Ni He-$\alpha $. The relative intensities of the resonance and intercombination and satellite lines show a clear angular dependence due to opacity effects. These effects will likely be important for interrupting scattered x-ray signals. Results from a CRF foam x-ray scattering experiment will also be presented. [Preview Abstract] |
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GP9.00111: Gold Charge State Distributions in Highly Ionized, Low-Density Beam Plasmas M. May, S. Hansen, M. Schneider, J. Scofield, K. Wong, P. Beiersdorfer The gold charge state distribution (CSD) has been experimentally inferred from Livermore electron beam ion traps EBIT-I and EBIT-II plasmas. Non-local thermodynamic equilibrium monoenergetic electron beams were created with E$_{BEAM}$ = 2.66, 2.92, 3.53 and 4.54 keV. Collisionally excited x-ray 5f$\rightarrow$3d and 4f$\rightarrow$3d line transitions from Ni-like to Kr-like Au having photon energies of 2 to 4 keV were recorded with a flat-crystal spectrometer. Radiative recombination spectra as well as collisionally excited 4f$\rightarrow$3d to 7f$\rightarrow$3d x-ray transitions were recorded from the beam plasmas with a photometrically calibrated x-ray microcalorimeter. The charge state distributions were inferred by fitting the measured lines in each spectral range with synthetic spectra. The SCRAM atomic physics code using atomic data from the flexible atomic code (FAC) was employed to calculate the CSD for each of the monoenergetic beam plasmas. These calculations significantly improved on previous calculations when dielectronic recombination states with high n (8$\leq$ n $\leq$20) were included in the models. These high-n DR states were critical in correctly predicting the experimentally determined CSDs. This work performed under the auspices of the US DoE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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GP9.00112: Spiral wobbling beam illumination uniformity in Heavy Ion Fusion S. Kawata, T. Kurosaki, S. Koseki, Y. Hisatomi, D. Barada, A.I. Ogoyski, B.G. Logan, J. Barnard A new beam illumination scheme has been found, in which a few per cent beam illumination nonuniformity is realized for a spiraling and ``wobbling'' beam in a heavy ion inertial confinement fusion (HIF) driver. The oscillating- HIB (heavy ion beam) energy deposition may produce a time-dependent implosion acceleration, which reduces both the Rayleigh-Taylor (R-T) growth [NIMA 606, 152(2009)] and the implosion nonuniformity. Three-dimensional HIB illumination computations indicate that the few per cent spiral-wobbling HIB illumination nonuniformity oscillates with the same wobbling HIB frequency. In HIF, HIB axes can be controlled precisely with a high frequency (100MHz $\sim $ 1GHz) centroid oscillation about the axis. This oscillating HIB creates a small oscillating energy deposition in time and space. This small oscillating nonuniformity can produce a small oscillating implosion acceleration nonuniformity. When the oscillation frequency is comparable to or larger than the R-T growth rate, it reduces the R-T growth significantly. [Preview Abstract] |
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GP9.00113: Fast Electron Angular Distribution and Conversion Efficiency Dependence on Laser Wavelngth and Pre-Puls Leonard Jarrott, Drew Higginson, Anna Sorokovikova, Brad Westover, Cliff Chen, Harry McLean, Prav Patel, Tony Link, Hal Friesen, Allan Beaudry, Jeffrey Tait, Jocelyn Westwood, Henry Tiedje, Ying Tsui, Robert Fedosejevs, Farhat Beg Experiments have been conducted using the Titan high-intensity laser ($50J$, $700fs$, $5\times10^{19}Wcm^{-2}$ at $2\omega$) to measure fast electron angular distribution and conversion efficiency from solid, multilayer targets using Hard X-ray Bremsstrahlung Spectrometers (HXBS) with 1$\omega$ and 2$\omega$ Nd:Glass laser pulses. An artificial pre-pulse from the Titan long pulse beam was then injected coaxially to the short pulse beam allowing for a systematic study of the effects of pre-pulse on fast electrons. Subsequent simulations were run using Integrated Tiger Suite (ITS) and Zuma to substantiate experimental data. The scaling of electron temperature, divergence, and conversion efficiency with pre-pulse will be presented. [Preview Abstract] |
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GP9.00114: Diagnosing and controlling mix in NIF implosion experiments B.A. Hammel, H.A. Scott, M.A. Barrios, C. Cerjan, D.S. Clark, M.J. Edwards, S.H. Glenzer, S.W. Haan, N. Izumi, J.A. Koch, O.L. Landen, T. Ma, L.J. Suter, S.P. Regan, R. Epstein, G.A. Kyrala, K. Peterson High mode number instability growth of ``isolated defects'' on the surfaces of NIF capsules can be large enough for the perturbation to penetrate the imploding shell and produce a jet of ablator material that enters the hot-spot. Since internal regions of the CH ablator are doped with Ge, mixing of this material into the hot-spot results in a clear signature of Ge K-shell emission. Evidence of jets entering the hot-spot has been recorded in x-ray images and spectra, consistent with simulation predictions.\footnote{B. A. Hammel, et al, High Energy Density Physics \textbf{- 6} (- 2) (2010). Prepared by LLNL under Contract DE-AC52-07NA27344.} Ignition targets have been designed to minimize instability growth, and capsule fabrication improvements are underway to reduce ``isolated defects.'' An experimental strategy has been developed where the final requirements for ignition targets can be adjusted through direct measurements of mix and experimental tuning. [Preview Abstract] |
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GP9.00115: Magnetohydrodynamics in Hydra J.M. Koning, G.D. Kerbel, M.M. Marinak The Magnetohydrodynamics package in the ALE radiation-hydrodynamics ICF design code Hydra is based upon a three-dimensional vector finite element method. This defines a set of spaces and differential operators that maintain the zero divergence of the magnetic field exactly. It is fully implicit in time and second order accurate in space. We discuss several improvements to the MHD package. The first addition is an anisotropic tensor based heat conduction method. The second improvement is a method for solving the magnetic diffusion equation for all of the element types resulting from point and line singularities including tetrahedral and pyramid elements. Finally a new magnetic flux advection method was implemented based on the method by A.C Robinson, et al.\footnote{A.C. Robinson, J. H. J. Niederhaus, V. G. Weirs, E. Love, Int. J. Numer. Meth. Fluids, 65, 1438 (2011)} [Preview Abstract] |
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GP9.00116: Integrated Design For Magnetically-Driven Liner Inertial Fusion of Preheated and Magnetized Fuel on the Z Accelerator A.B. Sefkow, K.J. Peterson, R.A. Vesey, S.A. Slutz, C.W. Nakhleh, J.M. Koning, M.M. Marinak Magnetically-driven implosions of metal liners containing magnetized and preheated fuel may enable significant ICF yields to be obtained on pulsed-power accelerators. Simulations of dense ($\rho$=1-5 mg/cc), axially-magnetized ($B_z$=3-30 T), and preheated ($T_i$=200-500 eV) DT fuel, driven by a pulsed-power accelerator similar to the Z machine ($I_{max}$=25-60 MA in 100-300 ns), indicate Gbar pressures and high yields ($E_{fus}$=100s kJ-10s MJ) may be feasible. Reduced heat conduction losses and alpha particle trapping can be provided by $B_z$ flux compression, and the fuel $\rho$$R$ ignition requirement is replaced by one for $B_z$$R$. Preheating the fuel prior to compression permits access to ignition temperatures without large convergence ratios or implosion velocities. Integrated simulations allow realistic designs for Z experiments ($I_{max}$=27 MA) with fuel preheat provided by the ZBL laser ($E_{las}$=2-6 kJ). Physics issues include laser deposition timing, evolution of thermal energy and $B_z$ field, magneto-RT instability growth, electrode and laser entrance hole end effects, and anisotropic conductivity and fusion burn in the $B_z$ field. Fusion yields on the order of the absorbed target energy may be possible on Z+ZBL, and high-gain designs using $I_{max}$=60 MA are studied. [Preview Abstract] |
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GP9.00117: Beam wobbler system and dynamic stabilization of Rayleigh-Taylor instability for heavy ion fusion Hong Qin, Ronald Davidson In recent studies of heavy ion fusion systems, it has been proposed to use a beam wobbler system to achieve uniform energy deposition on the target and to reduce the initial seeding for the Rayleigh-Taylor instability (RTI). Wobblers are set of biased electrical plates on the beam path driven by RF voltages to actively control the centroid dynamics of the beam so that different beam slices are delivered to different locations on the target. In addition, it turns out that the time-dependence of the energy deposition rendered by the wobbler system also introduces a significant dynamic stabilization effect for the RT instability. The two effects make the beam wobbler system an effective tool to suppress the RT instability for heavy ion fusion. [Preview Abstract] |
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GP9.00118: Non-collective X-ray Thomson scattering from warm dense beryllium Arthur Pak, Tammy Ma, Andrea Kritcher, Tilo Doeppner, Siegfried Glenzer Intense lasers can be used to shock compress solid materials creating warm dense matter (WDM), with free electron densities on the order of 10$^{24}$ cm$^{-3}$ and at temperatures of several eV. X-ray Thomson scattering (XRTS) can be used to diagnose the temperature, density, and charge state of such WDM. The temporal profile of the laser pulse can be shaped to quasi adiabaticly compress a solid, enabling higher shocked densities to be reached at relatively lower temperatures. In this work the effect of temporally shaping the laser pulse, to quasi adiabatically shock compress beryllium will be investigated utilizing XRTS. Experiments were preformed at the OMEGA-EP laser at the Laboratory for Laser Energetics (LLE). Initial results of the density, temperature and charge state from non-collective XRTS will be presented for the laser driven shock compression of beryllium. The effect on the inferred physical properties of the shock beryllium due to shaping the temporal profile of the laser pulse will be examined. [Preview Abstract] |
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GP9.00119: ABSTRACT WITHDRAWN |
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GP9.00120: Use of zooming and pulseshaping for acceleration to high velocities and fusion neutron production on the Nike laser Max Karasik, J.L. Weaver, Y. Aglitskiy, D.M. Kehne, S.T. Zalesak, A.L. Velikovich, J. Oh, S.P. Obenschain, Y. Arikawa We will present results from follow-on experiments to the record-high velocities of 1000~km/s achieved on Nike [Karasik et al, Phys.\ Plasmas 17, 056317(2010)], in which highly accelerated planar foils of deuterated polystyrene were made to collide with a witness foil to produce $\sim1$~Gbar shock pressures and result in heating of matter to thermonuclear temperatures. Still higher velocities and higher target densities are required for impact fast ignition. The aim of these experiments is using the focal zoom capability of Nike and shaping the driving pulse to minimize shock heating of the accelerated target to achieve higher densities and velocities. In-flight target density is inferred from target heating upon collision via DD neutron time-of-flight ion temperature measurement. Work is supported by US DOE (NNSA) and Office of Naval Research. [Preview Abstract] |
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GP9.00121: Stochastic modeling of statistically unsteady turbulent mixing A.T. Qamar, M. Cadjan, S.I. Abarzhi Rayleigh-Taylor and Richtmyer-Meshkov turbulent mixing are statistically unsteady processes. Their dynamics combines coherence and randomness, and their mean values and fluctuations are both time-dependent. These turbulent processes have a number of symmetries and are characterized by a set of invariant measures [EPL 91, 12867]. Employing these invariant measures, we developed a stochastic model for Rayleigh-Taylor and Richtmyer-Meshkov turbulent mixing in the case of sustained, time-dependent and impulsive acceleration. For the flow quantities, the effect of fluctuations on the mean values is studied and their statistical properties are analyzed. Requirements for statistical quality of experimental and numerical data are outlined. Mechanisms of mitigation and control of turbulent mixing processes are proposed. Their implementation in high energy density plasmas experiments is discussed. [Preview Abstract] |
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GP9.00122: The National Ignition Facility (NIF) as a User Facility Christopher Keane The 192-beam National Ignition Facility (NIF) at LLNL is operational and conducting experiments in ICF ignition and other areas of high energy density (HED) science. The National Ignition Campaign (NIC) conducts the NIF ignition program and provides the infrastructure for operation of NIF as a user facility. NIF has made significant progress towards operation as a user facility. The NIF laser has demonstrated the necessary performance to meet the needs of the ignition program and support experiments in fundamental HED science and other areas. A versatile set of diagnostics is installed and additional diagnostics are planned. A call for proposals in fundamental science has been executed and university-led experiments are in progress. A NIF User Group is being formed. This presentation will discuss implementation of NIF as a user facility, with emphasis on activities at NIF in fundamental science and other areas carried out in addition to the NIC. [Preview Abstract] |
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GP9.00123: Application of nonlocal transport model to experiment and implosion calculations in 1 and 2D Denis Colombant, Wallace Manheimer, Andrew Schmitt Our velocity-dependent Krook (VDK) model [1] has been applied to an experiment performed at the U. of Rochester [2] first. For the experimental comparison, we use our 2D version. This model involves applying time-split VDK in both the laser direction and that one perpendicular to it. We compare our model to the experimental results of acceleration of a thin foil, and also analyze the dependencies of critical information like temperature and density gradient scale-lengths on the various transport models. Although a judiciously chosen flux-limiter can reproduce a single observed variable, it cannot simultaneously match other variables. In particular, preheating effects are totally missed by such formulations. Implosion calculations where our VDK model is applied show the need to retune the laser pulse when nonlocal transport is included in order to ensure successful shock timing. Impact on target performance and stability parameters will be shown and discussed.\\[4pt] [1] D. Colombant and W. Manheimer, Phys. Plasmas, 17, 112706, 2010\\[0pt] [2] S.X. Hu, V.A. Smalyuk, V. Goncharov et al, Phys. Rev. Lett., 101, 055002, 2008 [Preview Abstract] |
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GP9.00124: Simulating hohlraum dynamics and radiation flow for Pleiades experiments on NIF K. Mussack, B.G. DeVolder, P.A. Keiter, J.L. Kline, N. Lanier, G.R. Magelssen, R.R. Peterson, J.M. Taccetti The Pleiades campaign is developing and validating an experimental platform on NIF to produce a high-quality radiation drive to study super-, trans- and subsonic radiation flow. Platform requirements include 5\% shot-to-shot repeatability, a minimum radiation drive of 300 eV, and the ability to provide supersonic radiation. Here we discuss the ongoing series of experiments, focusing on simulations of the hohlraum and package. We assess the platform's ability to provide the required drive and reproducibility, the effectiveness of spectral tailoring with M-band absorbing foam, and the ability of our models to simulate the hohlraum drive and radiation flow. Early shots in the campaign have met or surpassed requirements. The first shot produced a 340 eV drive, exceeding the minimum drive requirement. The Dante-measured flux from the second shot demonstrated success in meeting the repeatability requirement. Simulated Dante temperatures match both shots well, indicating that simulations successfully model the laser energy deposition and hohlraum dynamics. [Preview Abstract] |
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GP9.00125: Recent Developments in the VISRAD 3-D Target Design and Radiation Simulation Code Joseph MacFarlane, P. Woodruff, I. Golovkin The 3-D view factor code VISRAD is widely used in designing HEDP experiments at major laser and pulsed-power facilities, including NIF, OMEGA, OMEGA-EP, ORION, Z, and PLX. It simulates target designs by generating a 3-D grid of surface elements, utilizing a variety of 3-D primitives and surface removal algorithms, and can be used to compute the radiation flux throughout the surface element grid by computing element-to-element view factors and solving power balance equations. Target set-up and beam pointing are facilitated by allowing users to specify positions and angular orientations using a variety of coordinates systems ($e.g.$, that of any laser beam, target component, or diagnostic port). Analytic modeling for laser beam spatial profiles for OMEGA DPPs and NIF CPPs is used to compute laser intensity profiles throughout the grid of surface elements. VISRAD includes a variety of user-friendly graphics for setting up targets and displaying results, can readily display views from any point in space, and can be used to generate image sequences for animations. We will discuss recent improvements to the software package and plans for future developments. [Preview Abstract] |
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GP9.00126: Vlasov-Fokker-Planck simulations of magnetic field dynamics in inertial confinement fusion related scenarios Archis Joglekar, Alec Thomas In the interaction of high power laser beams with solid density plasma, there are a number of magnetic field generating mechanisms which result in very strong fields. This paper presents 2D simulations of near critical density plasma using a fully implicit Vlasov-Fokker-Planck code, IMPACTA, which includes self-consistent magnetic fields as well as anisotropic electron pressure terms in the expansion of the distribution function. Magnetic field generation and advection by heat flows is studied, particularly in the context of multiple laser spot heating where reconnection of magnetic field lines may occur. This is relevant to the interior of a hohlraum, where heating by multiple laser beams occurs. [Preview Abstract] |
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GP9.00127: On the Modeling of PHELIX and Other Pulsed-Power Experiments Christopher Rousculp, William Reass, David Oro, Peter Turchi, David Holtkamp, Jeffery Griego, Robert Reinovsky At LANL, pulsed power hydrodynamics employs multi mega-Amp currents, over tens of microseconds, producing hundreds of kilogauss fields in a Z-pinch configuration for the study of shocks, fluids, and material physics. The new PHELIX portable pulsed power machine demonstrated for first time the efficient coupling of a high-power capacitor bank via a toroidal transformer to a central load. The whole system sits on a 200 square foot platform for use at the LANL proton radiography facility. Additionally, magnetic FCGs are employed for very high energy density experiments. Here, explosives propel metal conductors in a coaxial, helical, or disk system to produce tens of mega-Amp currents. Currents carried in the skin depth are subject to intense Lorentz forces and Joule heating. Single-fluid, resistive MHD theory with material properties of the conductors well characterizes the experiments. One and two-dimensional computational codes solve the equations of mass, momentum, field, and energy. The grids are coupled to circuit equations describing the pulsed power driver. Results of recent experiments will be compared to modeling. [Preview Abstract] |
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GP9.00128: Modeling NIF Polar Direct Drive Capsule Implosions in 2D and 3D using HYDRA Natalia Krasheninnikova, Mark Schmitt, Sean Finnegan Simulations have been performed to determine the effects of asymmetries on direct drive NIF implosions. A 2.2 mm diameter, 30 micron thick CH capsule filled with 5 atmospheres DT was assumed. The radiation-hydrodynamic code HYDRA [1] was used to model the 96 NIF beams in the upper hemisphere impinging in a polar direct drive (PDD) configuration [2] on the capsule. Asymmetries in both polar and equatorial directions around the capsule were observed and analyzed. To assess the effects of removal of one of 50 degree quads for backlighting, 3D HYDRA simulations were preformed. The results showed that without re-pointing of the remaining beams in the ring, but with power compensation, the neutron yield was reduced over 70{\%}. However, simple beam realignment to repair the symmetry, restores the yield. Additional simulations to include the effects of high-mode number equatorial capsule defects have also been performed to assess their effects on symmetry and yield. The results of these simulations and their relation to similar PDD experiments recently performed at Omega will be shown. \\[4pt] [1] M. M. Marinak et al., Phys. Plasmas 3, 2070 (1996). \\[0pt] [2] A. M. Cok et al., Plasmas 15, 082705 (2008). [Preview Abstract] |
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GP9.00129: Influence of radiation field on Non-LTE Xe plasmas Marcel Klapisch, Michel Busquet Several experiments [1,2] and simulations of Xe were recently reported, due to the possibility of simulating scaled radiative shocks [3]. Extensive and systematic detailed computations using HULLAC [4] were performed for Te around 100eV and several densities, with initial conditions far or near LTE. The radiation is described as a Planckian at Trad multiplied by a dilution factor D. In each case, D is varied between 0 and 3 for Trad=Te, and Trad is varied from 0 to Te*1.5 with D=1. We show that in some cases, the dilution factor has more influence on the average charge Z* than the ratio Trad/Te, Taking into account radiation field is very important for evaluating Z* and non-LTE opacities. \\[4pt] [1] Keiter, P. A., Drake, R. P., Perry, T. S.\textit{, et al.}, Phys. Rev. Let. \textbf{89}, 165003 (2002).\\[0pt] [2] Busquet, M., Thais, F., Gonzalez, M.\textit{, et al.}, J. App. Phys. \textbf{107}, 083302 (2010). \\[0pt] [3] Ryutov, D., Drake, R. P., Kane, J.\textit{, et al.}, Astrophys. J. \textbf{518}, 821 (1999). \\[0pt] [4] Klapisch, M. and Busquet, M., High Ener. Dens. Phys. \textbf{5}, 105 (2009). [Preview Abstract] |
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GP9.00130: Electron transport simulations for non-uniformly laser-irradiated targets Michail Tzoufras, Tony Bell, Frank Tsung, Warren Mori To investigate electron transport in the context of the interaction of intense short-pulse lasers with plasmas, the density of which can range from less than critical to more than solid, we have developed the parallel 2D3P Vlasov-Fokker-Planck code OSHUN. OSHUN employs the expansion of the distribution function to spherical harmonics and allows retention of an arbitrary number of terms in the expansion to make it possible to treat distribution functions that substantially deviate from isotropy. A rigorous Fokker-Planck collision operator has been implemented, which recovers transport coefficients with excellent accuracy. One-dimensional Vlasov-Fokker-Planck modeling has indicated that non-local transport of laser-heated electrons can be beneficial to shock ignition by depositing the energy at higher density and by inhibiting losses to the plasma corona. Here we extend this study by using OSHUN to explore the multi-dimensional nature of non-local transport for simple geometries. This study aims to assess the effects of non-uniform irradiation on Shock Ignition targets and the possibility that non-local transport can sufficiently smooth an asymmetric irradiation profile to drive a spherically convergent shock. [Preview Abstract] |
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GP9.00131: Improvements to the High Energy Density Physics Capabilities in FLASH Shravan Kumar, J. Bachan, S. Couch, C. Daley, A. Dubey, M. Fatenejad, N. Flocke, C. Graziani, D.Q. Lamb, D. Lee, K. Weide FLASH is a modular and extensible compressible spatially adaptive radiation-hydrodynamics code that incorporates capabilities for a broad range of physical processes, performs well on a wide range of existing advanced computer architectures, and has a broad user base. We have been adding capabilities to FLASH to make it an open science code for the academic HEDP community. We summarize the improvements we have made to the HEDP capabilities of FLASH during the past year. A semi-implicit multi-group flux-limited diffusion solver has been implemented. A JFNK-based implicit hydrodynamic solver has been developed that relaxes stability constraints, leading to larger time steps. Numerous improvements have been made to the multi-material equation of state in FLASH and the laser ray-trace package. Finally, the results of several verification tests involving radiative/non-radiative shocks will also be presented. [Preview Abstract] |
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GP9.00132: MHD Development in FLAG James Reynolds, Konstantin Lipnikov, Christopher Rousculp, Ann Kaul, Jeff Peterson, Eric Nelson, Thomas Gianakon FLAG is a arbitrary polyhedral, rad-hydro, multi-fluid ALE code for modeling HEDP. A 1D/2D resistive MHD capability is implemented within FLAG to provide a predictive tool for modeling the driver and loads of pulsed power experiments that measure material properties in intense conditions. An overview of the FLAG MHD model is presented with verification results. Mimetic differencing schemes are methods that create discrete versions of PDE operators while preserving physical and geometric properties of the continuous operators [1]. Results are demonstrated for a Mimetic differencing approach to magnetic field diffusion and Joule heating. \\[4pt] [1] Brezzi, Lipnikov, Simoncini, M3AS: Math Mod and Methds in Ap Sci 15, 10 [Preview Abstract] |
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GP9.00133: Can high acceleration ICF target designs reduce the number of Rayleigh-Taylor exponentiations? Max Tabak The number of e-foldings for the classical Rayleigh-Taylor instability is linear in the velocity change. The required velocity change is set by fusion ignition conditions. However, the number of e-foldings is influenced by how fast this velocity change can be obtained. Shorter acceleration distances result in a lower number of e-foldings. For fixed drive intensity, this suggests a counter-intuitive design feature: increase the shell aspect ratio and the convergence ratio(for fixed fuel mass). This will produce high velocity in a short distance, but then what? If we continue to drive the shell at peak intensity, the shell will accelerate far past the optimal velocity and will burn-through. If we turn the drive off at this time, the shell will disassemble during the long coasting phase and jump to high adiabat at shell stagnation. The required pulse shape will reduce the drive after a required velocity is reached and later increase the drive to recompress the shell and lower its Mach number. Progress on this program will be discussed. [Preview Abstract] |
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GP9.00134: Generation and Growth of Magnetic Fields in Rayleigh-Taylor Unstable Plasmas Bhuvana Srinivasan, Guy Dimonte, Xianzhu Tang It has long been expected that Rayleigh-Taylor instabilities in ICF implosions can generate magnetic fields. To investigate this, a Hall-MHD model is used with the discontinuous Galerkin method in the code, WARPX (Washington Approximate Riemann Plasma). $2$-D single-mode and multi-mode studies of a Rayleigh-Taylor instability are performed in a stratified two-fluid plasma. Self-generated magnetic fields are observed and these fields grow ($\sim 10^2$T) as the Rayleigh-Taylor instability progresses. The $\nabla n_e \times \nabla T_e$ term in the generalized Ohm's law is responsible for the formation of a self-generated magnetic field. In the absence of this term in Ohm's law, no magnetic field forms. Scaling studies are performed to determine the growth of the self-generated magnetic field as a function of density, gravity, and perturbation wavelength. The magnetic field increases as the wavelength decreases, and as gravity increases, which is consistent with theory. Additionally, the MHD dynamo term, $v \times B$, is expected to further increase the magnetic field that is formed. An investigation of the coupling and growth of the MHD dynamo with the self-generated out-of-plane fields will enable us to estimate how large the fields will grow in $3$-D. [Preview Abstract] |
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GP9.00135: Self-Similar evolution of Richtmyer-Meshkov instability under re-shock conditions Guy Malamud, Eli Leinov, Asi Formoza, Oren Sadot, Arie Levin, Gabi Ben-Dor, Yonatan Elbaz, Dov Shvarts The Richtmyer-Meshkov (RM) instability is of critical importance in inertial confinement fusion (ICF) and astrophysics. In the present work a systematic study has been made of the growth of the turbulent mixing zone (TMZ) under re-shock conditions. In this study, shock-tube experiments were done by Leinov et al. [1] changing the re-shock arrival time, by varying the shock-tube end wall distance, as well as the shock Mach number. Using 3D direct numerical simulations as well as 3D bubble-competition model [2], for various initial 3D conditions, it was found that the best agreement with the experimental results is achieved when the TMZ evolution is dominated by the self-similar behavior of the bubble size and amplitude distributions. The TMZ power law at the first and second shock was deducted from the experimental and numerical data and compared with the results of the bubble competition model. [1] E. Leinov et. al. JFM, 626, 449(2009). [2] U. Alon et. al. PRL 72, 2867 (1994); D. Oron et. al. PoP 8, 2883 (2001); D. Kartoon et. al. LPB 21, 327 (2003). [Preview Abstract] |
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GP9.00136: Improvement of the LARED-H post-processing cod Xin Li The two-dimensional radiation hydrodynamic code LARED-H is developed to simulate hohlraums in ICF. The radiation transport is modelled through radiative heat conduction method. Experimentally measured radiation fluxes are calculated with a post-processing code solving multi-group transfer equations along appointed lines with absorption and emission coefficients coming from LARED-H simulations. Compared with hohlraum experiments, peak temperatures through the laser entrance hole and the 2-4 keV Au M-band fractions gave by the post-processing code are underestimated. The radiation transport model difference between LARED-H and its post-processing code is found to be the reason. Because the level populations coming from LARED-H simulations are not solved coupling with the multi-group equations in post-processing runnings, the post-processing code will give more radiation absorption and depress the net x-ray emission in laser spots finally. To solve this problem, the net x-ray emission of LARED-H simulations is included in the multi-group transfer equations. We find improved agreement between experiments and simulations using this new model [Preview Abstract] |
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GP9.00137: Hohlraum design for the LMJ ignition target G. Malinie, C. Cherfils, P. Gauthier, F. Lambert, M.C. Monteil First experiments with the Laser MegaJoule (LMJ) are scheduled to be performed in 2014. The current nominal point design for ignition with 160 beams on the LMJ has been described in [1]. It consists of an indirectly driven A943 capsule, with a plastic ablator doped with Germanium. This capsule is mounted in the center of a Rugby-shaped hohlraum, which is filled with a low density H/He gas, and has a gold-uranium cocktail wall lined with pure gold. We investigate the influence of two key parameters of the hohlraum design: the radius of the laser entrance holes (LEHs), and the thickness of the cocktail layer. Since the Rugby shape of the nominal point design is that of a half-ellipse going from the hohlraum waist to the LEH, any change in the LEH radius has a global effect on the hohlraum shape. Taking into account the current laser spot profiles of the LMJ and using 2D integrated calculations with our FCI2 radiation hydrodynamics code, we assess the flexiblility we have to reduce the LEH radius and/or the cocktail layer thickness. \\[4pt] [1] Laffite and Loiseau, Phys. Plasmas \textbf{17}, 102704 (2010) [Preview Abstract] |
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GP9.00138: The application of quasi-steady approximation in atomic kinetics in simulation of hohlraum radiation drive Guoli Ren, Wenbing Pei, Ke Lan, Peijun Gu, Xin Li In current routine 2D simulation of hohlraum physics, we adopt the principal-quantum- number(n-level) average atom model(AAM). However, the experimental frequency-dependant radiative drive differs from our n-level simulated drive, which reminds us the need of a more detailed atomic kinetics description. The orbital-quantum-number(nl-level) AAM is a natural consideration but the in-line calculation consumes much more resources. We use a new method to built up a nl-level bound electron distribution using in-line n-level calculated plasma condition (such as temperature, density, average ionization degree). We name this method ``quasi-steady approximation.'' Using the re-built nl-level bound electron distribution (P$_{nl})$, we acquire a new hohlraum radiative drive by post-processing. Comparison with the n-level post-processed hohlraum drive shows that we get an almost identical radiation flux but with more-detailed frequency-dependant structures. [Preview Abstract] |
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GP9.00139: The LIFE Dynamic Chamber System Mark Rhodes, Jave Kane, Jeffery Latkowski, Andrew Cook, Laurent Divol, Gwendolen Loosmore, Howard Scott, Christian Scullard, Max Tabak, Scott Wilks, Gregory Moses, Thad Heltemes, Ryan Sacks, Carlos Pantano, Richard Kramer Dry-wall IFE designs such as LIFE utilize Xe fill gas to protect the target chamber first wall from x-ray heating and ionic debris. A key question is how cool, settled and clean the Xe must be to permit beam propagation and target transport, and how to reach this state at a 10+ Hz shot repetition rate. Xe is at low density in the target chamber, and purified Xe is reinjected at higher density and lower temperature into the larger outer chamber. Maintenance of this density difference due to blast waves generated by implosion of the target capsules is being assessed with HYDRA and 3D VTF, and possible validation experiments are being investigated. Detailed gas response near the wall is being studied using 3D Miranda. A laboratory-scale theta pinch experiment will study cooling and beam propagation in Xe. [Preview Abstract] |
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