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May 2013

Volume 20, Issue 5 (partial)

Issue Cover Spotlight Figure

Phys. Plasmas 20, 056307 (2013); http://dx.doi.org/10.1063/1.4803092 (11 pages)

Bhuvana Srinivasan and Xian-Zhu Tang
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back to top Basic Plasma Phenomena, Waves, Instabilities

The expansion of a collisionless plasma into a plasma of lower density

M. Perego, P. D. Howell, M. D. Gunzburger, J. R. Ockendon, and J. E. Allen

Phys. Plasmas 20, 052101 (2013); http://dx.doi.org/10.1063/1.4802933 (16 pages)

Online Publication Date: 2 May 2013

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This paper considers the asymptotic and numerical solution of a simple model for the expansion of a collisionless plasma into a plasma of lower density. The dependence on the density ratio of qualitative and quantitative features of solutions of the well-known cold-ion model is explored. In the cold-ion limit, we find that a singularity develops in the ion density in finite time unless the density ratio is zero or close to unity. The classical cold-ion model may cease to be valid when such a singularity occurs and we then regularize the model by the finite ion-temperature Vlasov-Poisson system. Numerical evidence suggests the emergence of a multi-modal velocity distribution.
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52.25.Fi Transport properties
02.30.Jr Partial differential equations
02.60.-x Numerical approximation and analysis

Five-field simulations of peeling-ballooning modes using BOUT++ code

T. Y. Xia and X. Q. Xu

Phys. Plasmas 20, 052102 (2013); http://dx.doi.org/10.1063/1.4801006 (8 pages) | Cited 1 time

Online Publication Date: 2 May 2013

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The simulations of edge localized modes (ELMs) with a 5-field peeling-ballooning (P-B) model using BOUT++ code are reported in this paper. In order to study the particle and energy transport in the pedestal region, the pressure equation is separated into ion density and ion and electron temperature equations. Through the simulations, the length scale Ln of the gradient of equilibrium density ni0 is found to destabilize the P-B modes in ideal MHD model. With ion diamagnetic effects, the growth rate is inversely proportional to ni0 at medium toroidal mode number n. For the nonlinear simulations, the gradient of ni0 in the pedestal region can more than double the ELM size. This increasing effect can be suppressed by thermal diffusivities χ∥, employing the flux limited expression. Thermal diffusivities are sufficient to suppress the perturbations at the top of pedestal region. These suppressing effects lead to smaller ELM size of P-B modes.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.-b Plasma properties
52.25.Fi Transport properties
52.25.Kn Thermodynamics of plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Large amplitude inertial compressional Alfvénic shock and solitary waves, and acceleration of ions in magnetohydrodynamic plasmas

Anuraj Panwar, H. Rizvi, and C. M. Ryu

Phys. Plasmas 20, 052103 (2013); http://dx.doi.org/10.1063/1.4803064 (6 pages)

Online Publication Date: 3 May 2013

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Large amplitude inertial compressional Alfvénic shock and solitary waves in magnetohydrodynamic plasmas are investigated. Dispersive effect caused by non-ideal electron inertia currents perpendicular to the ambient magnetic field can balance the nonlinear steepening of waves leading to the formation of a soliton. A Sagdeev-potential formalism is employed to derive an energy-balance like equation. The range of allowed values of the soliton speed, M (Mach number), plasma β (ratio of the plasma thermal pressure to the pressure in the confining magnetic field), and electron inertia, wherein solitary waves may exist, are determined. Depth of the potential increases with increasing the Mach number and plasma β, however decreases with the increasing electron inertia. The height of soliton increases with increasing in Mach number and decreases with plasma β. And with increasing electron inertial length, the width of soliton increases. The electron-ion collisional dissipation results a dissipative inertial compressional Alfvén wave, which can produce a shock like structure and can efficiently accelerate ions to the order of the local Alfvén velocity. The shock height increases with the increasing collision frequency, but shock height decreases with increasing plasma β.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Sb Solitons; BGK modes
52.35.Tc Shock waves and discontinuities
52.20.Fs Electron collisions
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Ohmic losses in coaxial resonators with longitudinal inner-outer corrugation

A. Shenyong Hou, B. Sheng Yu, C. Hongfu Li, D. Qixiang Zhao, and E. Xiang Li

Phys. Plasmas 20, 052104 (2013); http://dx.doi.org/10.1063/1.4803649 (5 pages)

Online Publication Date: 6 May 2013

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In this paper, a coaxial resonator with longitudinal inner-outer corrugation is introduced. Its eigen-equation and expression of ohmic losses are derived. Ohmic losses in the cavity are investigated. Results show that ohmic losses in the outer and inner conductors share a similar variation trend, while the former is larger than the later. What's more, changes of the inner and outer slot depth and width induce different variations of ohmic losses on the surface of the inner and outer conductors.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
84.40.Az Waveguides, transmission lines, striplines

Magnetic piston model for higher ion charge and different electron and ion plasma temperatures

I. N. Bogatu

Phys. Plasmas 20, 052105 (2013); http://dx.doi.org/10.1063/1.4803651 (13 pages)

Online Publication Date: 6 May 2013

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A new formula for the magnetic piston model, which explicitly describes how the momentum imparted to the ions by the magnetic pressure depends not only on the ion mass but also on the ion charge, as well as, on the plasma electron and ion temperatures, is derived following Rosenbluth's classical particle-field self-consistent plane approximation analytic calculation. The formula presented in this paper has implications in explaining the experimentally observed separation of the ions of different species and charges by the magnetic field penetrating the plasma and specularly reflecting them.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.-b Plasma properties

Linear and nonlinear dynamics of electron temperature gradient mode in non-Maxwellian plasmas

U. Zakir, Q. Haque, and A. Qamar

Phys. Plasmas 20, 052106 (2013); http://dx.doi.org/10.1063/1.4803653 (6 pages)

Online Publication Date: 7 May 2013

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The effect of non-Maxwellian distributed ions on electron temperature gradient mode is investigated. The linear dispersion relation of ηe−mode is obtained which shows that the behavior of this mode changes in the presence of superthermal ions. The growth rate of ηe−mode driven linear instability is found and is observed to modify due to nonthermal ions. However, it is found that this leaves the electron energy transport coefficient unchanged. In the nonlinear regime, a dipolar vortex solution is derived which indicates that the dynamic behavior of the vortices changes with the inclusion of kappa distributed ions. The importance of present study with respect to space and laboratory plasmas is also pointed out.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.We Plasma vorticity
02.10.-v Logic, set theory, and algebra
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Multi-water-bag models of ion temperature gradient instability in cylindrical geometry

David Coulette and Nicolas Besse

Phys. Plasmas 20, 052107 (2013); http://dx.doi.org/10.1063/1.4804272 (13 pages)

Online Publication Date: 8 May 2013

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Ion temperature gradient instabilities play a major role in the understanding of anomalous transport in core fusion plasmas. In the considered cylindrical geometry, ion dynamics is described using a drift-kinetic multi-water-bag model for the parallel velocity dependency of the ion distribution function. In a first stage, global linear stability analysis is performed. From the obtained normal modes, parametric dependencies of the main spectral characteristics of the instability are then examined. Comparison of the multi-water-bag results with a reference continuous Maxwellian case allows us to evaluate the effects of discrete parallel velocity sampling induced by the Multi-Water-Bag model. Differences between the global model and local models considered in previous works are discussed. Using results from linear, quasilinear, and nonlinear numerical simulations, an analysis of the first stage saturation dynamics of the instability is proposed, where the divergence between the three models is examined.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Fi Transport properties
52.65.-y Plasma simulation
02.60.Cb Numerical simulation; solution of equations
52.25.Dg Plasma kinetic equations

Long wavelength gradient drift instability in Hall plasma devices. II. Applications

Winston Frias, Andrei I. Smolyakov, Igor D. Kaganovich, and Yevgeny Raitses

Phys. Plasmas 20, 052108 (2013); http://dx.doi.org/10.1063/1.4804281 (14 pages)

Online Publication Date: 8 May 2013

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Hall plasma devices with electron E × B drift are subject to a class of long wavelength instabilities driven by the electron current, gradients of plasma density, temperature, and magnetic field. In the first companion paper [Frias et al., Phys. Plasmas 19, 072112 (2012)], the theory of these modes was revisited. In this paper, we apply analytical theory to show that modern Hall thrusters exhibit azimuthal and axial oscillations in the frequency spectrum from tens KHz to few MHz, often observed in experiments. The azimuthal phase velocity of these modes is typically one order of magnitude lower than the E × B drift velocity. The growth rate of these modes scales inversely with the square root of the ion mass, ∼ 1/mathi. It is shown that several different thruster configurations share the same common feature: the gradient drift instabilities are localized in two separate regions, near the anode and in the plume region, and absent in the acceleration region. Our analytical results show complex interaction of plasma and magnetic field gradients and the E × B drift flow as the sources of the instability. The special role of plasma density gradient is revealed and it is shown that the previous theory is not applicable in the region where the ion flux density is not uniform. This is particularly important for near anode region due to ionization and in the plume region due to diverging ion flux.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Jm Ionization of plasmas

Geometrical parameters effects on local electric field enhancement of silver-dielectric-silver multilayer nanoshell

Farzad Shirzaditabar and Maryam Saliminasab

Phys. Plasmas 20, 052109 (2013); http://dx.doi.org/10.1063/1.4804345 (6 pages)

Online Publication Date: 8 May 2013

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The local electric field enhancement at different points of silver-dielectric-silver nanoshell is investigated using quasi-static theory. Because of the symmetric and anti-symmetric coupling between surface plasmon of inner silver core and outer silver shell, the local electric field spectrum of silver-dielectric-silver has two distinct peaks at resonance wavelengths. The silver core size and middle dielectric thickness affect the local electric field enhancement at different points of silver-dielectric-silver nanoshell. Increasing the silver core radius always leads to blue shift of shorter resonance wavelength and red shift of longer resonance wavelength. We observed two distinct local electric field peaks, which are corresponded to the symmetric and anti-symmetric coupling between inner and outer surface plasmons. In a system with thick silver shell, local electric field enhancement is greater than a system with thin silver shell. However, the local electric field variations as a function of silver core radius in both systems are different at different points of nanoshell. The effects of the dielectric thickness variations on local electric field are different from those from silver core size variations. As the dielectric thickness is about 3 nm, the highest local electric field enhancement occurs at the surface of the inner silver core, where the symmetric and anti-symmetric modes are mixed together.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.22.Lp Collective excitations
73.21.Ac Multilayers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
32.70.Jz Line shapes, widths, and shifts
78.68.+m Optical properties of surfaces

Gyrokinetic studies of microinstabilities in the reversed field pinch

D. Carmody, M. J. Pueschel, and P. W. Terry

Phys. Plasmas 20, 052110 (2013); http://dx.doi.org/10.1063/1.4803509 (8 pages)

Online Publication Date: 9 May 2013

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An analytic equilibrium, the Toroidal Bessel Function Model, is used in conjunction with the gyrokinetic code GYRO to investigate the nature of microinstabilities in a reversed field pinch plasma. The effect of the normalized electron plasma pressure β on the characteristics of the microinstabilities is studied. At a β of 4.5%, a transition between an ion temperature gradient (ITG) and a microtearing mode is observed. Suppression of the ITG mode occurs as in the tokamak, through coupling to shear Alfvén waves, with a critical β for stability higher than its tokamak equivalent due to a shorter parallel connection length. A steep dependence of the microtearing growth rate on the temperature gradient suggests high profile stiffness. There is evidence for a collisionless microtearing mode. The properties of this mode are investigated, and it is found that electron curvature drift plays an important role in the instability.
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52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Fa Tokamaks, spherical tokamaks
52.58.Lq Z-pinches, plasma focus, and other pinch devices
02.30.Gp Special functions

Bifurcations of nonlinear ion acoustic travelling waves in the frame of a Zakharov-Kuznetsov equation in magnetized plasma with a kappa distributed electron

Utpal Kumar Samanta, Asit Saha, and Prasanta Chatterjee

Phys. Plasmas 20, 052111 (2013); http://dx.doi.org/10.1063/1.4804347 (5 pages)

Online Publication Date: 10 May 2013

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Bifurcations of nonlinear propagation of ion acoustic waves (IAWs) in a magnetized plasma whose constituents are cold ions and kappa distributed electron are investigated using a two component plasma model. The standard reductive perturbation technique is used to derive the Zakharov-Kuznetsov (ZK) equation for IAWs. By using the bifurcation theory of planar dynamical systems to this ZK equation, the existence of solitary wave solutions and periodic travelling wave solutions is established. All exact explicit solutions of these travelling waves are determined. The results may have relevance in dense space plasmas.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Xz Magnetized plasmas
52.35.Sb Solitons; BGK modes
02.30.Oz Bifurcation theory
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
95.30.Qd Magnetohydrodynamics and plasmas

Frequency shift of the propagating ultraintense field in a plasma with a fraction of electron-positron pairs under the conditions of response saturation

O. B. Shiryaev

Phys. Plasmas 20, 052112 (2013); http://dx.doi.org/10.1063/1.4804351 (6 pages)

Online Publication Date: 10 May 2013

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A model is derived from the Maxwell and fluid dynamics equations to describe the interactions between a relativistically intense electromagnetic wave and a cold unmagnetized plasma composed of an electron-ion background and a fraction of electron-positron pairs. Combining the envelope approximation for the propagating field and the quasistatic treatment of the plasma dynamics, the model sustains fully nonlinear plane-wave solutions and shows that saturation of the plasma response occurs at ultrarelativistic intensities of the incident field even for pair concentrations far below those of the electron-ion background. Stability of the electromagnetic wave under the saturation conditions is demonstrated and an expression is derived to link its interaction-induced frequency shift to the concentration of the electron-positron pairs.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.20.Fs Electron collisions
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.27.Ny Relativistic plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Spontaneous electromagnetic fluctuations in unmagnetized plasmas. II. Relativistic form factors of aperiodic thermal modes

T. Felten, R. Schlickeiser, P. H. Yoon, and M. Lazar

Phys. Plasmas 20, 052113 (2013); http://dx.doi.org/10.1063/1.4804402 (14 pages)

Online Publication Date: 10 May 2013

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General expressions for the electromagnetic fluctuation spectra in unmagnetized plasmas are derived using fully relativistic dispersion functions and form factors for the important class of isotropic plasma particle distribution functions including in particular relativistic Maxwellian distributions. In order to obtain fluctuation spectra valid in the entire complex frequency plane, the proper analytical continuations of the unmagnetized form factors and dispersion functions are presented. The results are illustrated for the important special case of isotropic Maxwellian particle distribution functions providing in particular the thermal fluctuations of aperiodic modes. No restriction to the plasma temperature value is made, and the electromagnetic fluctuation spectra of ultrarelativistic thermal plasmas are calculated. The fully relativistic calculations also provide more general results in the limit of nonrelativistic plasma temperatures being valid in the entire complex frequency plane. They complement our earlier results in paper I and III of this series for negative values of the imaginary part of the frequency. A new collective, transverse, damped aperiodic mode with the damping rate γ∝−k−5/3 is discovered in an isotropic thermal electron-proton plasma with nonrelativistic temperatures.
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52.25.Gj Fluctuation and chaos phenomena
52.27.Ny Relativistic plasmas
52.25.Fi Transport properties
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Collisional effect on the Weibel instability with the bi-Maxwellian distribution function

M. Mahdavi and H. Khanzadeh

Phys. Plasmas 20, 052114 (2013); http://dx.doi.org/10.1063/1.4807035 (3 pages)

Online Publication Date: 15 May 2013

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In this paper, the Coulomb collision effect of electron-ion is investigated based on the equilibrium bi-Maxwellian anisotropic distribution function in dense and unmagnetized plasma. An analytical expression is derived for the real frequency and the growth rate of the Weibel instability for two limiting cases |ξ = math|≫1 and |ξ|≪1. In the limit |ξ|≪1, the quantity η that is due to a collisional term will appear in the growth and condition of the rate of the Weibel instability, which leads to a constraining condition of the growth rate. When η increases, the growth rate will increase and the wave instability will be distant from its own damping mode.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Fi Transport properties
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Resistive instability in a Hall plasma discharge under ionization effect

Hitendra K. Malik and Sukhmander Singh

Phys. Plasmas 20, 052115 (2013); http://dx.doi.org/10.1063/1.4804346 (8 pages)

Online Publication Date: 17 May 2013

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A systematic study is presented for low frequency resistive instability in a Hall plasma discharge under the effect of collisions, ionization, and finite temperature of ions and electrons by considering finite axial wave number. For this, a two dimensional dispersion equation is derived and solved numerically. Analytical calculations are also performed for obtaining the expression of growth rate and to discuss the limiting cases of equal axial (kx) and azimuthal (ky) wave numbers. The instability with higher growth rate is realized in the presence of ionization; the same is the case for equal wave numbers (kx = ky). However, the instability is suppressed when the ions and electrons carry higher temperatures, and weak effect of the electron temperature is observed for the case kx = ky.
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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)
02.60.-x Numerical approximation and analysis
52.25.Jm Ionization of plasmas
02.10.-v Logic, set theory, and algebra
52.80.-s Electric discharges

Second harmonic effect on geodesic modes in tokamak plasmas

A. G. Elfimov, A. I. Smolyakov, A. V. Melnikov, and R. M. O. Galvão

Phys. Plasmas 20, 052116 (2013); http://dx.doi.org/10.1063/1.4807039 (6 pages)

Online Publication Date: 22 May 2013

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Results of a kinetic treatment of Geodesic Acoustic Modes (GAMs) that fully takes into account ion parallel dynamics, including the magnetic field component, are presented. The finite-orbit-width (FOW) parameter is considered in the calculation of the second harmonic effect on GAMs. For larger values of the FOW parameter, it is shown that dispersive effects related to the m = 2 harmonics is the cause of the mode frequency splitting and the modes appear due to the interaction with the ion sound mode. Furthermore, the modes may have enhanced damping rates due to second harmonic Landau damping.
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52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.55.Jd Magnetic mirrors, gas dynamic traps
52.55.Fa Tokamaks, spherical tokamaks
52.35.Kt Drift waves
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
back to top Nonlinear Phenomena, Turbulence, Transport

Phase mixing of upper hybrid oscillations in a cold inhomogeneous plasma placed in an inhomogeneous magnetic field

Anwesa Sarkar, Chandan Maity, and Nikhil Chakrabarti

Phys. Plasmas 20, 052301 (2013); http://dx.doi.org/10.1063/1.4803654 (6 pages)

Online Publication Date: 6 May 2013

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We study phase mixing/wave breaking phenomena of upper hybrid modes in a cold inhomogeneous plasma placed in an inhomogeneous magnetic field. Inhomogeneities both in the background ion density and magnetic field profile are treated as periodic in space but independent in time. The Lagrangian fluid description is employed to obtain an exact solution of this fully nonlinear problem. It is demonstrated that the upper hybrid modes, excited by an initial local charge imbalance, break via phase mixing, induced by the inhomogeneities. It is also shown that it is possible to avoid phase mixing in excited upper hybrid oscillations in an inhomogeneous plasma containing a finite amplitude ion density fluctuation. The choice of external magnetic field is shown to have a key role in avoiding phase mixing in such oscillations. The relevance of our investigation regarding the particle acceleration in an inhomogeneous plasma has also been discussed.
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52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Global two-fluid simulations of geodesic acoustic modes in strongly shaped tight aspect ratio tokamak plasmas

J. R. Robinson, B. Hnat, A. Thyagaraja, K. G. McClements, P. J. Knight, A. Kirk, and MAST Team

Phys. Plasmas 20, 052302 (2013); http://dx.doi.org/10.1063/1.4804271 (6 pages)

Online Publication Date: 7 May 2013

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Following recent observations suggesting the presence of the geodesic acoustic mode (GAM) in ohmically heated discharges in the Mega Amp Spherical Tokamak (MAST) [J. R. Robinson et al., Plasma Phys. Controlled Fusion 54, 105007 (2012)], the behaviour of the GAM is studied numerically using the two fluid, global code CENTORI [P. J. Knight et al. Comput. Phys. Commun. 183, 2346 (2012)]. We examine mode localisation and effects of magnetic geometry, given by aspect ratio, elongation, and safety factor, on the observed frequency of the mode. An excellent agreement between simulations and experimental data is found for simulation plasma parameters matched to those of MAST. Increasing aspect ratio yields good agreement between the GAM frequency found in the simulations and an analytical result obtained for elongated large aspect ratio plasmas.
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52.55.Fa Tokamaks, spherical tokamaks
52.80.-s Electric discharges
52.65.Kj Magnetohydrodynamic and fluid equation
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)

Dynamics of low dimensional model for weakly relativistic Zakharov equations for plasmas

Biswajit Sahu, Barnali Pal, Swarup Poria, and Rajkumar Roychoudhury

Phys. Plasmas 20, 052303 (2013); http://dx.doi.org/10.1063/1.4804340 (7 pages)

Online Publication Date: 8 May 2013

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In the present paper, the nonlinear interaction between Langmuir waves and ion acoustic waves described by the one-dimensional Zakharov equations (ZEs) for relativistic plasmas are investigated formulating a low dimensional model. Equilibrium points of the model are found and it is shown that the existence and stability conditions of the equilibrium point depend on the relativistic parameter. Computational investigations are carried out to examine the effects of relativistic parameter and other plasma parameters on the dynamics of the model. Power spectrum analysis using fast fourier transform and also construction of first return map confirm that periodic, quasi-periodic, and chaotic type solution exist for both relativistic as well as in non-relativistic case. Existence of supercritical Hopf bifurcation is noted in the system for two critical plasmon numbers.
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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.)
52.27.Ny Relativistic plasmas

Mass dependency of turbulent parameters in stationary glow discharge plasmas

J. B. Titus, D. L. Wiggins, A. B. Alexander, and J. A. Johnson, III

Phys. Plasmas 20, 052304 (2013); http://dx.doi.org/10.1063/1.4804339 (5 pages)

Online Publication Date: 10 May 2013

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A direct current glow discharge tube is used to determine how mass changes the effects of certain turbulence characteristics in a weakly ionized gas. Helium, neon, argon, and krypton plasmas were created, and an axial magnetic field, varied from 0.0 to 550.0 Gauss, was used to enhance mass dependent properties of turbulence. From the power spectra of light emission variations associated with velocity fluctuations, determination of mass dependency on turbulent characteristic unstable modes, energy associated with turbulence, and the rate at which energy is transferred from scale to scale are measured. The magnetic field strength is found to be too weak to overcome particle diffusion to the walls to affect the turbulence in all four types of plasmas, though mass dependency is still detected. Though the total energy and the rate at which the energy moves between scales are mass invariant, the amplitude of the instability modes that characterize each plasma are dependent on mass.
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52.80.Hc Glow; corona
52.50.Dg Plasma sources
52.35.Ra Plasma turbulence
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.25.Kn Thermodynamics of plasmas
52.25.Fi Transport properties

Coupled electron and ion nonlinear oscillations in a collisionless plasma

A. R. Karimov

Phys. Plasmas 20, 052305 (2013); http://dx.doi.org/10.1063/1.4803070 (6 pages)

Online Publication Date: 22 May 2013

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Dynamics of coupled electrostatic electron and ion nonlinear oscillations in a collisionless plasma is studied with reference to a kinetic description. Proceeding from the exact solution of Vlasov-Maxwell equations written as a function of linear functions in the electron and ion velocities, we arrive at the two coupled nonlinear equations which describe the evolution of the system.
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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.)
52.65.Ff Fokker-Planck and Vlasov equation
02.30.-f Function theory, analysis
52.25.Dg Plasma kinetic equations
back to top Magnetically Confined Plasmas, Heating, Confinement

Comparison of toroidicity-induced Alfvén eigenmodes and energetic particle modes by gyrokinetic particle simulations

Chenxi Zhang, Wenlu Zhang, Zhihong Lin, and Ding Li

Phys. Plasmas 20, 052501 (2013); http://dx.doi.org/10.1063/1.4803502 (9 pages)

Online Publication Date: 2 May 2013

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This work reports on linear global gyrokinetic particle simulations of the excitation of toroidicity-induced Alfvén eigenmodes (TAE) and energetic particle modes (EPM), and the comparison between these two modes. The TAE excitation by antenna clarifies the magnetohydrodynamic (MHD) mode structure and the discrete eigenmode exists in the gap between the upper and lower accumulation points. The TAE excitation by fast ions modifies the MHD mode structure because of radial symmetry breaking and the eigenmode frequency moves towards the lower accumulation point. The phase space structure of fast ions shows that both passing and trapped particles contribute to the TAE excitation and that trapped particles dominate the wave-particle resonance in our simulations. The growth rate of TAE is sensitive to the fast ion energy, density, and density gradient, which are also important factors contributing to the transition of the TAE to the EPM. The gyrokinetic particle simulations also confirm the excitation of EPM when the drive is stronger. The frequency of the EPM is determined by the characteristic frequencies of fast ion motion in toroidal geometry.
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52.65.Tt Gyrofluid and gyrokinetic simulations
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides

Disruption avoidance in the SINP-Tokamak by means of electrode-biasing at the plasma edge

Debjyoti Basu, Rabindranath Pal, Julio J. Martinell, Joydeep Ghosh, and Prabal K. Chattopadhyay

Phys. Plasmas 20, 052502 (2013); http://dx.doi.org/10.1063/1.4803656 (7 pages)

Online Publication Date: 6 May 2013

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Control of plasma disruption by a biased edge electrode is reported in SINP-Tokamak. The features that characterize a plasma disruption are reduced with increasing bias potential. The disruption can be completely suppressed with the concomitant stabilization of observed MHD modes that are allegedly precursors of the disruption. An m = 3/n = 1 tearing mode, which apparently causes disruption can be stabilized when a negative biasing potential is applied near the edge. These changes in the disruptive behavior with edge biasing are hypothesized to be due to changes in the current density profile.
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52.55.Tn Ideal and resistive MHD modes; kinetic modes
52.25.Xz Magnetized plasmas
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks

A complete theory for the magnetism of an ideal gas of electrons

Shyamal Biswas, Swati Sen, and Debnarayan Jana

Phys. Plasmas 20, 052503 (2013); http://dx.doi.org/10.1063/1.4804274 (7 pages)

Online Publication Date: 8 May 2013

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We have explored Pauli paramagnetism, Landau diamagnetism, and de Haas-van Alphen effect in a single framework, and unified these three effects for all temperatures as well as for all strengths of magnetic field. Our result goes beyond Pauli-Landau result on the magnetism of the 3-D ideal gas of electrons, and is able to describe crossover of the de Haas-van Alphen oscillation to the saturation of magnetization. We also have obtained a novel asymptotic series expansion for the low temperature properties of the system.
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75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
05.30.Fk Fermion systems and electron gas
71.10.Ca Electron gas, Fermi gas
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

A biased probe analysis of potential well formation in an electron only, low beta Polywell magnetic field

Matthew Carr and Joe Khachan

Phys. Plasmas 20, 052504 (2013); http://dx.doi.org/10.1063/1.4804279 (10 pages)

Online Publication Date: 9 May 2013

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Orbital limited motion theory has been applied to two biased probes in a low beta Polywell. The cases studied include electron injection, magnetic field scaling, Polywell bias scaling, and radial position profiles. Langmuir's original orbital limited motion results for a monoenergetic electron beam are shown to be in excellent agreement for electron injection into the Polywell. A distribution function is proposed for the electron plasma characteristics in the centre of the magnetic null and confirmed with experimental results. A translational stage was used to measure the radial plasma potential profile. In other experiments, two probes were used to simultaneously measure the profiles in both the null and a position halfway along a corner cusp. The results confirm a radial potential well created by electron trapping in the device. In addition, we present preliminary results of the potential well scaling with the magnetic field, Polywell bias voltage, and the injected beam current. The electron population was found to maintain non-equilibrium in all cases studied.
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52.70.Ds Electric and magnetic measurements
52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.25.Fi Transport properties
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