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Jan 2005

Volume 12, Issue 1, Articles (01xxxx)

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Generation and measurements of high energy injection electrons from the high density laser ionization and ponderomotive acceleration

A. Ting, D. Kaganovich, D. F. Gordon, R. F. Hubbard, and P. Sprangle

Phys. Plasmas 12, 010701 (2005); http://dx.doi.org/10.1063/1.1819937 (4 pages) | Cited 6 times

Online Publication Date: 23 November 2004

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The high density regime of the laser ionization and ponderomotive acceleration (HD-LIPA) injector provides high injection bunch charge by employing a high density gas jet. Measurements and simulations confirmed that space charge effects lead to a distribution of high energy LIPA electrons in the directly forward directions in violation of the LIPA angle-energy relationship. These electrons also have much higher energies than predicted, indicating that further acceleration by mechanisms such as the self-modulated laser wakefield acceleration may be present in the HD-LIPA environment.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.80.-s Electric discharges
52.75.Di Ion and plasma propulsion
52.59.Sa Space-charge-dominated beams
52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.65.Rr Particle-in-cell method
52.25.Jm Ionization of plasmas

Experimental observation of resonance overlap responsible for Hamiltonian chaos

F. Doveil, Kh. Auhmani, A. Macor, and D. Guyomarc’h

Phys. Plasmas 12, 010702 (2005); http://dx.doi.org/10.1063/1.1824040 (4 pages) | Cited 13 times

Online Publication Date: 3 December 2004

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A test electron beam is propagated in a specially designed traveling wave tube. The beam intensity is low enough to ensure that beam-plasma instabilities are ruled out. By recording the beam energy distribution at the output of the tube, we report the experimental observation of the resonant domain of a single wave and of the overlap of the resonance domains of two waves associated to the destruction of Kolmogorov–Arnold–Moser tori constituting barriers in phase space. This overlap mechanism is responsible for the transition to large scale chaos common to a large class of Hamiltonian systems.
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52.40.Mj Particle beam interactions in plasmas
52.25.Gj Fluctuation and chaos phenomena
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
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back to top Basic Plasma Phenomena, Waves, Instabilities

Motion of guiding center drift atoms in the electric and magnetic field of a Penning trap

S. G. Kuzmin and T. M. O’Neil

Phys. Plasmas 12, 012101 (2005); http://dx.doi.org/10.1063/1.1818140 (13 pages) | Cited 5 times

Online Publication Date: 23 November 2004

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The ApparaTus for High precision Experiment on Neutral Antimatter and antihydrogen TRAP collaborations have produced antihydrogen atoms by recombination in a cryogenic antiproton-positron plasma. This paper discusses the motion of the weakly bound atoms in the electric and magnetic field of the plasma and trap. The effective electric field in the moving frame of the atom polarizes the atom, and then gradients in the field exert a force on the atom. An approximate equation of motion for the atom center of mass is obtained by averaging over the rapid internal dynamics of the atom. The only remnant of the atom internal dynamics that enters this equation is the polarizability for the atom. This coefficient is evaluated for the weakly bound and strongly magnetized (guiding center drift) atoms understood to be produced in the antihydrogen experiments. Application of the approximate equation of motion shows that the atoms can be trapped radially in the large space charge field near the edge of the positron column. Also, an example is presented for which there is full three-dimensional trapping, not just radial trapping. Even untrapped atoms follow curved trajectories, and such trajectories are discussed for the important class of atoms that reach a field ionization diagnostic. Finally, the critical field for ionization is determined as an upper bound on the range of applicability of the theory.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.20.Dq Particle orbits
52.80.Sm Magnetoactive discharges (e.g., Penning discharges)
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Nc Particle measurements
52.25.Fi Transport properties

Study of small-amplitude magnetohydrodynamic surface waves on liquid metal

Hantao Ji, William Fox, David Pace, and H. L. Rappaport

Phys. Plasmas 12, 012102 (2005); http://dx.doi.org/10.1063/1.1822933 (13 pages) | Cited 4 times

Online Publication Date: 23 November 2004

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Magnetohydrodynamic (MHD) surface waves on liquid metal are studied theoretically and experimentally in the small magnetic Reynolds number limit. A linear dispersion relation is derived when a horizontal magnetic field and a horizontal electric current is imposed. Waves always damp in the deep liquid limit with a magnetic field parallel to the propagation direction. When the magnetic field is weak, waves are weakly damped and the real part of the dispersion is unaffected, while in the opposite limit waves are strongly damped with shortened wavelengths. In a table-top experiment, planar MHD surface waves on liquid gallium are studied in detail in the regime of weak magnetic field and deep liquid. A noninvasive diagnostic accurately measures surface waves at multiple locations by reflecting an array of lasers off the surface onto a screen, which is recorded by an intensified-CCD (charge-coupled device) camera. The measured dispersion relation is consistent with the linear theory with a reduced surface tension likely due to surface oxidation. In excellent agreement with linear theory, it is observed that surface waves are damped only when a horizontal magnetic field is imposed parallel to the propagation direction. No damping is observed under a perpendicular magnetic field. The existence of strong wave damping even without magnetic field suggests the importance of the surface oxide layer. Implications to the liquid metal wall concept in fusion reactors, especially on the wave damping and a Rayleigh–Taylor instability when the Lorentz force is used to support liquid metal layer against gravity, are discussed.
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47.35.-i Hydrodynamic waves
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
47.65.-d Magnetohydrodynamics and electrohydrodynamics

Second harmonic electromagnetic emission via beam-driven Langmuir waves

B. Li, A. J. Willes, P. A. Robinson, and I. H. Cairns

Phys. Plasmas 12, 012103 (2005); http://dx.doi.org/10.1063/1.1812274 (15 pages) | Cited 23 times

Online Publication Date: 23 November 2004

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The linked nonlinear processes of electrostatic Langmuir decay and electromagnetic emission at the second harmonic plasma frequency are studied for situations in which Langmuir waves are driven by an electron beam. An approximate method for studying wave decay and emission in three spatial dimensions is developed, based on the Langmuir and ion-acoustic wave dynamics in one spatial dimension. The numerical solutions of quasilinear equations to study electromagnetic emission starting from the electron dynamics are carried out. The numerical results are explored for illustrative parameters. The evolution of the transverse waves shows the combined effects of local emission and propagation away from the source. At a given location, the emission rate shows a series of peaks associated with coalescences of Langmuir waves driven by the beam and those produced by successive decays. The emission rate for a given coalescence decreases with time, following an initial increase. The effects of transverse wave propagation are illustrated by the presence of transverse waves both in regions upstream of the beam injection site due to backward propagation, and in regions downstream (e.g., where Langmuir waves are at thermal levels prior to the arrival of the beam) owing to forward propagation. Variation of the background electron to ion temperature ratio, beam injection parameters, and angular widths of the Langmuir spectra are found to affect the emission rate and the transverse wave levels. Furthermore, detailed studies show that the wave numbers of the maximum emission rates are in semiquantitative agreement with a previous theoretical prediction for simple model Langmuir spectra.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.Dg Plasma kinetic equations
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.40.Mj Particle beam interactions in plasmas
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

The electrostatic sheath in an electronegative dusty plasma

Zheng-Xiong Wang, Jin-Yuan Liu, Yue Liu, and Xiaogang Wang

Phys. Plasmas 12, 012104 (2005); http://dx.doi.org/10.1063/1.1824909 (5 pages) | Cited 8 times

Online Publication Date: 6 December 2004

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Bohm criterion for the electrostatic sheath in electronegative dusty plasmas, which are composed of electrons, negative and positive ions, as well as dust grains, is investigated with Sagdeev potential, taking into account the self-consistent dust charge variation. The numerical solutions show that the dust and negative ion densities, as well as the positive ion and dust Bohm velocities, all have effects on the dust charge at the sheath edge. The positive ion and dust Bohm velocities increase with the growth of the dust density, while both of them decrease with the growth of negative ion density. Furthermore, the interactions between the two Bohm velocities are considered. The results are examined and found to be reliable by the quantitative analysis of Sagdeev potential.
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52.40.Kh Plasma sheaths
52.27.Lw Dusty or complex plasmas; plasma crystals
52.25.Fi Transport properties
52.27.Cm Multicomponent and negative-ion plasmas

Drift kinetic equation exact through second order in gyroradius expansion

Andrei N. Simakov and Peter J. Catto

Phys. Plasmas 12, 012105 (2005); http://dx.doi.org/10.1063/1.1823414 (9 pages) | Cited 21 times

Online Publication Date: 14 December 2004

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The drift kinetic equation of Hazeltine [ R. D. Hazeltine, Plasma Phys. 15, 77 (1973) ] for a magnetized plasma of arbitrary collisionality is widely believed to be exact through the second order in the gyroradius expansion. It is demonstrated that this equation is only exact through the first order. The reason is that when evaluating the second-order gyrophase dependent distribution function, Hazeltine neglected contributions from the first-order gyrophase dependent distribution function, and then used this incomplete expression to derive the equation for the gyrophase independent distribution function. Consequently, the second-order distribution function and the stress tensor derived by this approach are incomplete. By relaxing slightly Hazeltine’s orderings one is able to obtain a drift kinetic equation accurate through the second order in the gyroradius expansion. In addition, the gyroviscous stress tensor for plasmas of arbitrary collisionality is obtained.
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52.25.Dg Plasma kinetic equations
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.20.-j Elementary processes in plasmas
52.25.Fi Transport properties
52.25.Xz Magnetized plasmas

Extensions of adiabatic invariant theory for a charged particle

Harold Weitzner and Choong-Seock Chang

Phys. Plasmas 12, 012106 (2005); http://dx.doi.org/10.1063/1.1829653 (10 pages) | Cited 2 times

Online Publication Date: 14 December 2004

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The standard theory of Hamiltonian dynamics of a charged particle is extended to allow electric and magnetic fields to vary across magnetic field lines or surfaces on the Larmor radius distance scale. After the development of the general theory, the special cases of toroidally nested magnetic surfaces and of axisymmetry are considered. In a further restriction the situation with spatially slowly varying static magnetic fields but spatially rapidly varying static bounded electrostatic potentials is treated. The dynamics of the perpendicular velocity is represented by a nonlinear oscillator. The adiabatic invariant and drift Hamiltonian are constructed near an O point in the perpendicular velocity phase plane. Motion near a separatrix and X point in physical space is also briefly explored.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.20.Dq Particle orbits
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Resonance between continuous spectra: Secular behavior of Alfvén waves in a flowing plasma

M. Hirota, T. Tatsuno, and Z. Yoshida

Phys. Plasmas 12, 012107 (2005); http://dx.doi.org/10.1063/1.1834591 (11 pages) | Cited 7 times

Online Publication Date: 22 December 2004

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Conventional normal mode analysis often falls short in predicting a variety of transient phenomena in a non-self-adjoint (non-Hermitian) system. Laplace transform is capable of capturing all possible behavior in general systems. However, degenerate essential spectra require careful analysis. The Alfvén wave in a flowing plasma is an example in which the coalescence of the Alfvén singularities yields nonexponential growth of fluctuations. Invoking hyperfunction theory, rigorous expression of the Laplace transform leads to an accurate estimate of the asymptotic behavior of resonant singular modes.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.25.Gj Fluctuation and chaos phenomena
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Tn Ideal and resistive MHD modes; kinetic modes
02.30.Uu Integral transforms
back to top Nonlinear Phenomena, Turbulence, Transport

Effects of positron concentration, ion temperature, and plasma β value on linear and nonlinear two-dimensional magnetosonic waves in electron–positron–ion plasmas

A. Mushtaq and H. A. Shah

Phys. Plasmas 12, 012301 (2005); http://dx.doi.org/10.1063/1.1814115 (11 pages) | Cited 25 times

Online Publication Date: 23 November 2004

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Magnetosonic waves are intensively studied due to their importance in space plasmas and also in fusion plasmas where they are used in particle acceleration and heating experiments. This work considers magnetosonic waves propagating obliquely at an angle θ to an external magnetic field in an electron–positron–ion plasma, using the effective one-fluid magnetohydrodynamic model. Two separate modes (fast and slow) for the waves are discussed in the linear approximation, and the Kadomstev–Petviashvilli soliton equation is derived by using reductive perturbation scheme for these modes in the nonlinear regime. It is observed that for both the modes the angle θ, positron concentration, ion temperature, and plasma β-value affect the propagation properties of solitary waves and behave differently from the simple electron–ion plasmas. Likewise, current density, electric field, and magnetic field for these waves are investigated, for their dependence on the above mentioned parameters.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Sb Solitons; BGK modes
52.25.Fi Transport properties
52.27.Cm Multicomponent and negative-ion plasmas

Modified Zakharov equations for plasmas with a quantum correction

L. G. Garcia, F. Haas, L. P. L. de Oliveira, and J. Goedert

Phys. Plasmas 12, 012302 (2005); http://dx.doi.org/10.1063/1.1819935 (8 pages) | Cited 28 times

Online Publication Date: 3 December 2004

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Quantum Zakharov equations are obtained to describe the nonlinear interaction between quantum Langmuir waves and quantum ion-acoustic waves. These quantum Zakharov equations are applied to two model cases, namely, the four-wave interaction and the decay instability. In the case of the four-wave instability, sufficiently large quantum effects tend to suppress the instability. For the decay instability, the quantum Zakharov equations lead to results similar to those of the classical decay instability except for quantum correction terms in the dispersion relations. Some considerations regarding the nonlinear aspects of the quantum Zakharov equations are also offered.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Dm Sound waves

Accelerated electron populations formed by Langmuir wave-caviton interactions

N. J. Sircombe, T. D. Arber, and R. O. Dendy

Phys. Plasmas 12, 012303 (2005); http://dx.doi.org/10.1063/1.1822934 (8 pages) | Cited 13 times

Online Publication Date: 3 December 2004

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Direct numerical simulations of electron dynamics in externally driven electrostatic waves have been carried out using a relativistic two-fluid one-dimensional Vlasov–Poisson code. When the driver wave has sufficiently large amplitude, ion density holes (cavitons) form. The interaction between these cavitons and other incoming Langmuir waves gives rise to substantial local acceleration of groups of electrons, and fine jetlike structures arise in electron phase space. We show that these jets are caused by wave breaking when finite amplitude Langmuir waves experience the ion density gradient at the leading edge of the holes, and are not caused by caviton burnout. An analytical two-fluid model gives the critical density gradient and caviton depth for which this process can occur. In particular, the density gradient critically affects the rate at which a Langmuir wave, moving into the caviton, undergoes Landau damping. This treatment also enables us to derive analytical estimates for the maximum energy of accelerated electrons, and for the energy spectrum along a phase-space jet. These are confirmed by direct numerical simulations.
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52.75.Di Ion and plasma propulsion
52.40.Mj Particle beam interactions in plasmas
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.Ff Fokker-Planck and Vlasov equation
52.27.Ny Relativistic plasmas
02.60.Lj Ordinary and partial differential equations; boundary value problems

Bihelical magnetic relaxation and large scale magnetic field growth

Eric G. Blackman

Phys. Plasmas 12, 012304 (2005); http://dx.doi.org/10.1063/1.1822935 (11 pages) | Cited 4 times

Online Publication Date: 3 December 2004

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A unified, three-scale system of equations accommodating nonlinear velocity driven helical dynamos, as well as time-dependent relaxation of magnetically dominated unihelical or bihelical systems is derived and solved herein. When opposite magnetic helicities of equal magnitude are injected on the intermediate and small scales, the large scale magnetic helicity grows kinematically (independent of the magnetic Reynolds number) to equal that on the intermediate scale. For both free and driven relaxation large scale fields are rapidly produced. Subsequently, a dissipation-limited dynamo, driven by growth of small scale kinetic helicity, further amplifies the large scale field. The results are important for astrophysical coronae fed with bihelical structures by dynamos in their host rotators. The large scale for the rotator corresponds to the intermediate scale for the corona. That bihelical magnetic relaxation can produce global scale fields may help to explain the formation of astrophysical coronal holes and magnetohydrodynamic outflows.
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52.25.Dg Plasma kinetic equations
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.80.Hc Glow; corona
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties
95.30.Qd Magnetohydrodynamics and plasmas

Structure of reconnection layer with a shear flow perpendicular to the antiparallel magnetic field component

Xiaoxia Sun, Yu Lin, and Xiaogang Wang

Phys. Plasmas 12, 012305 (2005); http://dx.doi.org/10.1063/1.1826096 (8 pages) | Cited 5 times

Online Publication Date: 3 December 2004

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A one-dimensional resistive magnetohydrodynamic (MHD) simulation of the Riemann problem is carried out for the structure of reconnection layer, i.e., outflow region of quasisteady magnetic reconnection, in the presence of a sheared flow tangential to the initial current (Jy) sheet. Unlike previous studies, the shear flow is in the y direction, perpendicular to the antiparallel component of the magnetic field Bz, with a total change of flow ΔVy ≠ 0 across the current sheet. Cases with symmetric or asymmetric current sheet and various guide magnetic fields By are investigated. The simulation shows that in the reconnection layer, the structure of MHD discontinuities changes significantly with the strength of the shear flow. The main findings are the following: (1) In the case initially with a zero guide field (By = 0, for the so-called “antiparallel reconnection”), the shear flow in Vy produces a finite By in the reconnection layer and two time-dependent intermediate shocks with rotation angle of tangential magnetic field less than 180°. (2) For initial By ≠ 0 (the “component reconnection”) the sheared Vy leads to very different magnetic field structures in the two outflow regions on the two sides of the X line. (3) In the cases with the initial By ≠ 0, the existence of the sheared Vy can lead to the reversal of the rotation sense of tangential magnetic field through the reconnection layer. The critical value of ΔVy for the occurrence of this field reversal is discussed. The general simulation results can be applied to space and laboratory plasmas.
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52.35.Vd Magnetic reconnection
52.35.Tc Shock waves and discontinuities
52.30.−q

Exact models for Hall current reconnection with axial guide fields

I. J. D. Craig and P. G. Watson

Phys. Plasmas 12, 012306 (2005); http://dx.doi.org/10.1063/1.1826094 (9 pages) | Cited 9 times

Online Publication Date: 6 December 2004

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This paper employs an analytic reconnection model to investigate the conditions under which Hall currents can influence reconnection and Ohmic dissipation rates. It is first noted that time dependent magnetohydrodynamic systems can be analyzed by decomposing the magnetic and velocity fields into guide field and reconnecting field components. A formally exact solution shows that Hall currents can speed up or slow down the reconnection rate depending on the strength and orientation of the axial guide field. In particular, merging solutions are developed in which the axial guide field is the dominant driver of the reconnection. The extent to which Hall currents can alleviate the buildup of back pressures in flux pile-up reconnection models is also examined. The analysis shows that, although enhancements of the merging rate can be expected under certain conditions, it is unlikely that Hall currents can completely undo the fundamental pressure limitations associated with flux pile-up reconnection.
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52.35.Vd Magnetic reconnection
52.25.Fi Transport properties

Large amplitude parallel propagating electromagnetic oscillitons

Tom Cattaert and Frank Verheest

Phys. Plasmas 12, 012307 (2005); http://dx.doi.org/10.1063/1.1824038 (7 pages) | Cited 4 times

Online Publication Date: 9 December 2004

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Earlier systematic nonlinear treatments of parallel propagating electromagnetic waves have been given within a fluid dynamic approach, in a frame where the nonlinear structures are stationary and various constraining first integrals can be obtained. This has lead to the concept of oscillitons that has found application in various space plasmas. The present paper differs in three main aspects from the previous studies: first, the invariants are derived in the plasma frame, as customary in the Sagdeev method, thus retaining in Maxwell’s equations all possible effects. Second, a single differential equation is obtained for the parallel fluid velocity, in a form reminiscent of the Sagdeev integrals, hence allowing a fully nonlinear discussion of the oscilliton properties, at such amplitudes as the underlying Mach number restrictions allow. Third, the transition to weakly nonlinear whistler oscillitons is done in an analytical rather than a numerical fashion.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.30.Ex Two-fluid and multi-fluid plasmas
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb Solitons; BGK modes
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.27.Cm Multicomponent and negative-ion plasmas
02.30.Hq Ordinary differential equations

The role of high frequency oscillations in the penetration of plasma clouds across magnetic boundaries

Tomas Hurtig, Nils Brenning, and Michael A. Raadu

Phys. Plasmas 12, 012308 (2005); http://dx.doi.org/10.1063/1.1812276 (13 pages) | Cited 11 times

Online Publication Date: 9 December 2004

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Experiments are reported where a collissionfree plasma cloud penetrates a magnetic barrier by self-polarization. Three closely related effects, all fundamental for the penetration mechanism, are studied quantitatively: (1) anomalous fast magnetic field penetration (two orders of magnitude faster than classical), (2) anomalous fast electron transport (three orders of magnitude faster than classical and two orders of magnitude faster than Bohm diffusion), and (3) the ion energy budget as ions enter the potential structure set up by the self-polarized plasma cloud. It is concluded that all three phenomena are closely related and that they are mediated by highly nonlinear oscillations in the lower hybrid range, driven by a strong diamagnetic current loop which is set up in the plasma in the penetration process. The fast magnetic field penetration occurs as a consequence of the anomalous resistivity caused by the wave field and the fast electron transport across magnetic field lines is caused by the correlation between electric field and density oscillations in the wave field. It is also found that ions do not lose energy in proportion to the potential “hill” they have to climb, rather they are transported against the dc potential structure by the same correlation that is responsible for the electron transport. The results obtained through direct measurements are compared to particle in cell simulations that reproduce most aspects of the high frequency wave field.
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52.25.Fi Transport properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.65.Rr Particle-in-cell method
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Conditions for plasmoid penetration across abrupt magnetic barriers

Nils Brenning, Tomas Hurtig, and Michael A. Raadu

Phys. Plasmas 12, 012309 (2005); http://dx.doi.org/10.1063/1.1812277 (10 pages) | Cited 12 times

Online Publication Date: 9 December 2004

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The penetration of plasma clouds, or plasmoids, across abrupt magnetic barriers (of the scale less than a few ion gyro radii, using the plasmoid directed velocity) is studied. The insight gained earlier, from detailed experimental and computer simulation investigations of a case study, is generalized into other parameter regimes. It is concluded for what parameters a plasmoid should be expected to penetrate the magnetic barrier through self-polarization, penetrate through magnetic expulsion, or be rejected from the barrier. The scaling parameters are ne, v0, B⊥, mi, Ti, and the width w of the plasmoid. The scaling is based on a model for strongly driven, nonlinear magnetic field diffusion into a plasma which is a generalization of the earlier laboratory findings. The results are applied to experiments earlier reported in the literature, and also to the proposed application of impulsive penetration of plasmoids from the solar wind into the Earth’s magnetosphere.
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52.25.Fi Transport properties
94.30.Va Magnetosphere interactions
96.60.Vg Particle emission, solar wind
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Excitation of zonal flows by kinetic Alfvén waves

P. K. Shukla

Phys. Plasmas 12, 012310 (2005); http://dx.doi.org/10.1063/1.1826095 (4 pages) | Cited 17 times

Online Publication Date: 14 December 2004

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Nonlinear couplings between dispersive kinetic Alfvén waves (DKAWs) and electrostatic convective cells∕zonal flows are reexamined. A set of equations that exhibit nonlinear couplings between the scalar and parallel vector potentials of the DKAWs and the scalar potential of zonal flows that are reinforced by the Reynolds stresses of the DKAWs in a magnetized plasma is presented. The equations are then Fourier-analyzed to obtain the nonlinear dispersion relation. The latter exhibits modulational instabilities, which could be responsible for enhanced zonal flows in a uniform magnetized plasma. Zonal flows can regulate the transport of plasma particles in laboratory magnetoplasmas as well as in the Earth’s magnetosphere and in the solar corona.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Xz Magnetized plasmas

Gyrokinetic δf simulation of the collisionless and semicollisional tearing mode instability

W. Wan, Y. Chen, and S. E. Parker

Phys. Plasmas 12, 012311 (2005); http://dx.doi.org/10.1063/1.1827216 (8 pages) | Cited 11 times

Online Publication Date: 14 December 2004

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The evolution of collisionless and semicollisional tearing mode instabilities is studied using an electromagnetic gyrokinetic δf particle-in-cell simulation model. Drift-kinetic electrons are used. Linear eigenmode analysis is presented for the case of fixed ions and there is excellent agreement with simulation. A double peaked eigenmode structure is seen indicative of a positive Δ′. Nonlinear evolution of a magnetic island is studied and the results compare well with existing theory in terms of saturation level and electron bounce oscillations. Electron-ion collisions are included to study the semicollisional regime. The algebraic growth stage is observed and compares favorably with theory. Nonlinear saturation following the algebraic stage is observed.
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52.65.Rr Particle-in-cell method
52.20.Fs Electron collisions
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Positron acceleration to ultrarelativistic energies by an oblique magnetosonic shock wave in an electron-positron-ion plasma

Hiroki Hasegawa and Yukiharu Ohsawa

Phys. Plasmas 12, 012312 (2005); http://dx.doi.org/10.1063/1.1827624 (7 pages) | Cited 2 times

Online Publication Date: 14 December 2004

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Positron acceleration in a shock wave in a plasma consisting of electrons, positrons, and ions is studied with theory and simulations. From the relativistic equation of motion, it is found that an oblique shock wave can accelerate some positrons with the energy increase rate proportional to E∙B. They move nearly parallel to the external magnetic field, staying in the shock transition region for long periods of time. Then, this acceleration is demonstrated with one-dimensional, relativistic, electromagnetic particle simulations with full particle dynamics. Some positrons have been accelerated to ultrarelativistic energies (γ ∼ 1000) with this mechanism. Parametric study of this acceleration is also made.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Tc Shock waves and discontinuities
52.65.Cc Particle orbit and trajectory
52.27.Ny Relativistic plasmas
52.27.Cm Multicomponent and negative-ion plasmas

Bernstein mode aided anomalous absorption of laser in a plasma

Asheel Kumar and V. K. Tripathi

Phys. Plasmas 12, 012313 (2005); http://dx.doi.org/10.1063/1.1811619 (6 pages)

Online Publication Date: 14 December 2004

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A laser propagating through a plasma, in the presence of an electron Bernstein wave, undergoes nonlinear mode coupling, producing a beat mode (ω+ω0, k+k0) where (ω0, k0) and (ω, k) are the frequency and wave number of the laser and the Bernstein mode. The oscillatory electron velocity associated with this beat mode couples with electron density perturbation due to the Bernstein wave to produce a nonlinear current at the laser frequency. When the beat mode is Landau damped on electrons, the nonlinear current at the laser frequency has an in-phase component with the laser field, giving rise to anomalous resistivity. The normalized anomalous resistivity is found to be maximum for q = ∣k+k0∣νth/(ω+ω0) ≈ 0.8–0.9.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Nonplanar dust-ion acoustic shock waves with transverse perturbation

Ju-Kui Xue

Phys. Plasmas 12, 012314 (2005); http://dx.doi.org/10.1063/1.1829298 (5 pages) | Cited 10 times

Online Publication Date: 14 December 2004

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The nonlinear dust-ion acoustic shock waves in dusty plasmas with the combined effects of bounded cylindrical/spherical geometry, the transverse perturbation, the dust charge fluctuation, and the nonthermal electrons are studied. Using the perturbation method, a cylindrical/spherical Kadomtsev–Petviashvili Burgers equation that describes the dust-ion acoustic shock waves is deduced. A particular solution of the cylindrical/spherical Kadomtsev–Petviashvili Burgers equation is also obtained. It is shown that the dust-ion acoustic shock wave propagating in cylindrical/spherical geometry with transverse perturbation will be slightly deformed as time goes on.
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52.35.Sb Solitons; BGK modes
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.27.Jt Nonneutral plasmas

A physical mechanism of nonthermal plasma effect on shock wave

S. P. Kuo and Steven S. Kuo

Phys. Plasmas 12, 012315 (2005); http://dx.doi.org/10.1063/1.1829295 (5 pages) | Cited 3 times

Online Publication Date: 14 December 2004

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An electric discharge is applied to generate a plasma spike in front of a wedge. Use of this plasma spike to modify the shock wave structure in a supersonic flow over the wedge is then studied. It is shown that the plasma spike can effectively deflect the incoming flow before the flow reaches the wedge; consequently, the shock structure in the interaction region is modified from an oblique to a curved shape. Moreover, the shock becomes detached as the strength of the plasma spike exceeds a critical level.
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52.35.Tc Shock waves and discontinuities
52.80.-s Electric discharges
52.30.-q Plasma dynamics and flow

Linear and nonlinear stability analysis for two-dimensional ideal magnetohydrodynamics with incompressible flows

A. H. Khater, S. M. Moawad, and D. K. Callebaut

Phys. Plasmas 12, 012316 (2005); http://dx.doi.org/10.1063/1.1828464 (10 pages) | Cited 5 times

Online Publication Date: 15 December 2004

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The equilibrium and Lyapunov stability properties for two-dimensional ideal magnetohydrodynamic (MHD) plasmas with incompressible and homogeneous (i.e., constant density) flows are investigated. In the unperturbed steady state, both the velocity and magnetic field are nonzero and have three components in a Cartesian coordinate system with translational symmetry (i.e., one ignorable spatial coordinate). It is proved that (a) the solutions of the ideal MHD steady state equations with incompressible and homogeneous flows in the plane are also valid for equilibria with the axial velocity component being a free flux function and the axial magnetic field component being a constant, (b) the conditions of linearized Lyapunov stability for these MHD flows in the planar case (in which the fields have only two components) are also valid for symmetric equilibria that have a nonplanar velocity field component as well as a nonplanar magnetic field component. On using the method of convexity estimates, nonlinear stability conditions are established.
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52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
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