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A. J. Brizard

Publications and source records attributed to A. J. Brizard.

16 recordsLinked to original sources

Metriplectic bracket for guiding-center Vlasov-Maxwell-Landau theory

The metriplectic formulation of collisional guiding-center Vlasov-Maxwell-Landau theory is presented. The guiding-center Landau collision operator, which describes collisions involving test-particle and field-particle guiding-center orbits, is represented in terms of a symmetric dissipative bracket involving functional derivatives of the guiding-center Vlasov phase-space density $F_{\rm gc}$ and the electromagnetic fields $({\bf D}_{\rm gc},{\bf B})$, where the guiding-center displacement vector ${\bf D}_{\rm gc} \equiv {\bf E} + 4π\,{\sf P}_{\rm gc}$ is expressed in terms of the electric field ${\bf E}$ and the guiding-center polarization ${\sf P}_{\rm gc}$. This dissipative Landau bracket conserves guiding-center energy-momentum and angular momentum, as well as satisfying a guiding-center H-theorem.

physics.plasm-ph

Exact expressions for nonperturbative guiding center theory in symmetric fields

We apply a recently-developed nonperturbative guiding center formalism to charged particle dynamics in fields with two-parameter continuous symmetry groups. This entails finding exact constants of motion, valid in the nonperturbative regime, that agree with Kruskal's adiabatic invariant series to all orders in the perturbative regime, when the field scale length is large compared with a typical gyroradius. We demonstrate that the nonperturbative guiding center model makes exact predictions in these cases, even though it eliminates the cyclotron timescale, thereby establishing a theoretical baseline for performance of the nonperturbative formalism.

physics.plasm-ph

Gauge-free electromagnetic gyrokinetic theory

A new gauge-free electromagnetic gyrokinetic theory is developed, in which the gyrocenter equations of motion and the gyrocenter phase-space transformation are expressed in terms of the perturbed electromagnetic fields, instead of the usual perturbed potentials. Gyrocenter polarization and magnetization are derived explicitly from the gyrocenter Hamiltonian, up to first order in the gyrocenter perturbation expansion. Expressions for the sources in Maxwell's equations are derived in a form that is suitable for simulation studies, as well as kinetic-gyrokinetic hybrid modeling.

physics.plasm-ph

Lifting of the Vlasov-Maxwell Bracket by Lie-transform Method

The Vlasov-Maxwell equations possess a Hamiltonian structure expressed in terms of a Hamiltonian functional and a functional bracket. In the present paper, the transformation ("lift") of the Vlasov-Maxwell bracket induced by the dynamical reduction of single-particle dynamics is investigated when the reduction is carried out by Lie-transform perturbation methods. The ultimate goal of this work is to derive explicit Hamiltonian formulations for the guiding-center and gyrokinetic Vlasov-Maxwell equations that have important applications in our understanding of turbulent magnetized plasmas. Here, it is shown that the general form of the reduced Vlasov-Maxwell equations possesses a Hamiltonian structure defined in terms of a reduced Hamiltonian functional and a reduced bracket that automatically satisfies the standard bracket properties.

physics.plasm-ph

Equivalent Higher-order Guiding-center Hamiltonian Theories

Equivalent guiding-center Hamiltonian theories are constructed based on higher-order Lie-transform perturbation methods. Higher-order guiding-center theories are distinguished on the basis of whether correction terms associated with magnetic-field nonuniformity appear either in the guiding-center symplectic (Poisson-bracket) structure, in the guiding-center Hamiltonian, or both. These theories are called equivalent because they describe the same guiding-center magnetic-moment invariant. The present work presents the detailed derivations of results that were summarized in a recent paper by Tronko and Brizard [Phys. Plasmas 22, 112507 (2015)].

physics.plasm-ph

Variational principles for the guiding-center Vlasov-Maxwell equations

The Lagrange, Euler, and Euler-Poincaré variational principles for the guiding-center Vlasov-Maxwell equations are presented. Each variational principle presents a different approach to deriving guiding-center polarization and magnetization effects into the guiding-center Maxwell equations. The conservation laws of energy, momentum, and angular momentum are also derived by Noether method, where the guiding-center stress tensor is now shown to be explicitly symmetric.

physics.plasm-ph

Energetically-consistent collisional gyrokinetics

We present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory.

physics.plasm-ph

Compact formulas for bounce/transit averaging in axisymmetric tokamak geometry

Compact formulas for bounce and transit orbit averaging of the fluctuation-amplitude eikonal factor in axisymmetric tokamak geometry, which is frequently encountered in bounce-gyrokinetic description of microturbulence, are given in terms of the Jacobi elliptic functions and elliptic integrals. These formulas are readily applicable to the calculation of the neoclassical susceptibility in the framework of modern bounce-gyrokinetic theory. In the long-wavelength limit for axisymmetric electrostatic perturbations, we recover the expression for the Rosenbluth-Hinton residual zonal flow [Rosenbluth and Hinton, Phys.~Rev.~Lett.~{\bf 80}, 724 (1998)] accurately.

physics.plasm-ph

Hamiltonian formulation of the gyrokinetic Vlasov-Maxwell equations

The gyrokinetic Vlasov-Maxwell equations are cast as an infinite-dimensional Hamiltonian system. The gyrokinetic Poisson bracket is remarkably simple and similar to the Morrison-Marsden-Weinstein bracket for the Vlasov-Maxwell equations. By identifying many of the bracket's Casimirs, this work enables (i) the derivation of gyrokinetic equilibrium variational principles and (ii) the application of the energy-Casimir method and the method of dynamically-accessible variations to study stability properties of gyrokinetic equilibria.

physics.plasm-ph

Perturbation analysis of trapped-particle dynamics in axisymmetric dipole geometry

The perturbation analysis of the bounce action-angle coordinates $(J,ζ)$ for charged particles trapped in an axisymmetric dipole magnetic field is presented. First, the lowest-order bounce action-angle coordinates are derived for deeply-trapped particles in the harmonic-oscillator approximation. Next, the Lie-transform perturbation method is used to derive higher-order anharmonic action-angle corrections. Explicit expressions (with anharmonic corrections) for the canonical parallel coordinates $s(J,ζ)$ and $p_{\|}(J,ζ)$ are presented, which satisfy the canonical identity $\{s,\; p_{\|}\}(J,ζ) \equiv 1$. Lastly, analytical expressions for the bounce and drift frequencies (which include anharmonic corrections) yield excellent agreement with exact numerical results.

physics.plasm-ph

Orbit-averaged Guiding-center Fokker-Planck Operator

A general orbit-averaged guiding-center Fokker-Planck operator suitable for the numerical analysis of transport processes in axisymmetric magnetized plasmas is presented. The orbit-averaged guiding-center operator describes transport processes in a three-dimensional guiding-center invariant space: the orbit-averaged magnetic-flux invariant $\ovψ$, the minimum-B pitch-angle coordinate $ξ_{0}$, and the momentum magnitude $p$.

physics.plasm-ph

Guiding-center recursive Vlasov and Lie-transform methods in plasma physics

The gyrocenter phase-space transformation used to describe nonlinear gyrokinetic theory is rediscovered by a recursive solution of the Hamiltonian dynamics associated with the perturbed guiding-center Vlasov operator. The present work clarifies the relation between the derivation of the gyrocenter phase-space coordinates by the guiding-center recursive Vlasov method and the method of Lie-transform phase-space transformations.

physics.plasm-ph

Nonlinear finite-Larmor-radius effects in reduced fluid models

The polarization and magnetization effects associated with the dynamical reduction leading to the nonlinear gyrokinetic Vlasov-Maxwell equations are shown to introduce nonlinear finite-Larmor-radius effects into a set of nonlinear reduced-fluid equations previously derived by Lagrangian variational method [A.J. Brizard, Phys. Plasmas 12, 092302 (2005)]. These intrinsically nonlinear FLR effects, which are associated with the transformation from guiding-center phase-space dynamics to gyrocenter phase-space dynamics, are different from the standard FLR corrections associated with the transformation from particle to guiding-center phase-space dynamics. We also present the linear dispersion relation and results from a nonlinear simulation code using these reduced-fluid equations. The simulation results (in both straight and dipole geometries) demonstrate that the equations describe the coupled dynamics of Alfven and sound waves and that the total simulation energy is conserved.

physics.plasm-ph

Analysis of ray phase-space recirculation in an extended Budden problem

A three-wave Budden model with two resonance layers is constructed that allows recirculation of energy fluxes along a quadrangle in ray phase space. The transmission, reflection, and conversion coefficients for this extended Budden problem are calculated by ray phase-space methods and the modular-eikonal approach. Analytical and numerical results show that all coefficients exhibit interference effects that depend on an interference phase calculated from the coupling constants and the area enclosed by the quadrangle.

physics.plasm-ph

Nonlocal Nonlinear Electrostatic Gyrofluid Equations: A four-moment model

Extending a previous single-temperature model, an electrostatic gyrofluid model that includes anisotropic temperatures (parallel and perpendicular) and can treat general nonlinear situations is constructed. The model is based on a Lagrangian formulation of gyrofluid dynamics, which leads to an exact energy conservation law. Diamagnetic cancelations are inserted manually in such a way that energy conservation is preserved. Comparison with previous models shows a very good agreement for zero-Larmor-radius terms in the gyrofluid equations of motion.

physics.plasm-ph

Mini-Conference on Hamiltonian and Lagrangian Methods in Fluid and Plasma Physics

A mini-conference on Hamiltonian and Lagrangian methods in fluid and plasma physics was held on November 14, 2002, as part of the 44th meeting of the Division of Plasma Physics of the American Physical Society. This paper summarizes the material presented during the talks scheduled during the Mini-Conference, which was held to honor Allan Kaufman on the occasion of his 75th birthday.

physics.plasm-ph