Comparative study of the surface potential of magnetic and non-magnetic spherical objects in a magnetized radio-frequency discharge

We report measurements of the time-averaged surface floating potential of magnetic and non-magnetic spherical probes (or large dust particles) immersed in a magnetized capacitively coupled discharge. In this study, the size of the spherical probes is taken greater than the Debye length. The surface potential of a spherical probe first increases, i.e. becomes more negative at low magnetic field ( $B < 0.05\ \textrm {T}$ ), attains a maximum value and decreases with further increase of the magnetic field strength ( $B > 0.05\ \textrm {T}$ ). The rate of change of the surface potential in the presence of a $B$ -field mainly depends on the background plasma and types of material of the objects. The results show that the surface potential of the magnetic sphere is higher (more negative) compared with the non-magnetic spherical probe. Hence, the smaller magnetic sphere collects more negative charges on its surface than a bigger non-magnetic sphere in a magnetized plasma. The different sized spherical probes have nearly the same surface potential above a threshold magnetic field ( $B > 0.03\ \textrm {T}$ ), implying a smaller role of size dependence on the surface potential of spherical objects. The variation of the surface potential of the spherical probes is understood on the basis of a modification of the collection currents to their surface due to charge confinement and cross-field diffusion in the presence of an external magnetic field.

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Electrostatic Rossby-type ion plasma waves

Journal of Plasma Physics ◽

10.1017/s0022377800012885 ◽

1988 ◽

Vol 39 (1) ◽

pp. 103-114 ◽

Cited By ~ 2

Author(s):

J. F. McKenzie ◽

M. K. Dougherty

Keyword(s):

Magnetic Field ◽

Rossby Wave ◽

Vertical Component ◽

Rotational Frequency ◽

Rate Of Change ◽

Magnetized Plasma ◽

Propagation Mechanism ◽

Wave Operators ◽

Geostrophic Balance ◽

Background Magnetic Field

It is shown that a plasma in which the background magnetic field varies in a direction perpendicular to its line of action can support ‘Rossby-type’ electrostatic waves at frequencies very much less than the ion gyrofrequency. The intrinsic wave propagation mechanism at work is structurally similar to that in the atmospheric Rossby wave, which comes about from fluid perturbations being in quasi-geostrophic equilibrium (i.e. the Coriolis force nearly balances the pressure gradient) and the latitudinal variation of the vertical component of rotational frequency vector (the β-effect) so that the time rate of change of the vertical component of the fluid vorticity is equal to the northward transport of the planetary vorticity. In a plasma this ‘geostrophic balance’ arises from the near-vanishing of the Lorentz force on the ion motion while the β-effect is provided by the transverse spatial variation of the ambient magnetic field. Unlike the atmosphere, however, such a magnetized plasma is capable of supporting two distinct types of Rossby wave. The interesting dispersive and anisotropic features of these waves are revealed by the properties of their wave operators and described in terms of the geometry of their wavenumber surfaces. Since these surfaces intersect, inhomogeneity or nonlinearity will give rise to strong mode-mode coupling in regions where the phases of both modes nearly match.

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Floating surface potential of spherical dust grains in magnetized plasmas

Journal of Plasma Physics ◽

10.1017/s0022377815001464 ◽

2016 ◽

Vol 82 (1) ◽

Cited By ~ 4

Author(s):

Dennie Lange

Keyword(s):

Magnetic Field ◽

Debye Length ◽

Magnetized Plasma ◽

Gyration Radius ◽

Theory Approach ◽

Dust Grains ◽

Particle In Cell ◽

Charging Current ◽

Simulation Results ◽

Ion Charging

A particle-in-cell (PIC) simulation study of the charging processes of spherical dust grains in a magnetized plasma environment is presented. Different magnetic field strengths with corresponding electron/ion gyration radii of smaller, the same or larger size than the grain radius and the plasma Debye length are examined. The magnetized plasma is created by overlapping the simulation box with a homogeneous, constant magnetic field. The charging currents are significantly reduced in the presence of a magnetic field, resulting in a more negative grain floating potential. Indeed, the most probable electron gyration radius is always smaller than that of ions in a Maxwellian plasma: however, it is demonstrated that the situation of simultaneous magnetized electron but an unmagnetized ion charging current never exists. The simulation results do not fit with a modified orbital motion limited (OML) theory approach for this situation, since the ion current is significantly reduced due to the increase of the gyration radius in the potential field of the dust grain. For very small gyration radii, the simulation results are in good agreement with a modified OML approach for both magnetized electron and ion charging currents.

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Laser Assisted Dirac Electron in a Magnetized Annulus

Symmetry ◽

10.3390/sym13040642 ◽

2021 ◽

Vol 13 (4) ◽

pp. 642

Author(s):

Emilio Fiordilino

Keyword(s):

Magnetic Field ◽

Analytical Form ◽

Relative Energy ◽

Radial Force ◽

Rate Of Change ◽

Orthogonal Direction ◽

Linearly Polarized ◽

Dirac Electron ◽

A Charge ◽

Stretching Effect

We study the behaviour of a charge bound on a graphene annulus under the assumption that the particle can be treated as a massless Dirac electron. The eigenstates and relative energy are found in closed analytical form. Subsequently, we consider a large annulus with radius ρ∈[5000,10,000]a0 in the presence of a static magnetic field orthogonal to its plane and again the eigenstates and eigenenergies of the Dirac electron are found in both analytical and numerical form. The possibility of designing filiform currents by controlling the orbital angular momentum and the magnetic field is shown. The currents can be of interest in optoelectronic devices that are controlled by electromagnetic radiation. Moreover, a small radial force acts upon the annulus with a stretching effect. A linearly polarized electromagnetic field propagating in the orthogonal direction is added; the time evolution of the operators show that the acceleration of the electron is proportional to the rate of change of the spin of the particle.

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Polarimetric and photometric observations of CB54, with analysis of four other dark clouds

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab380 ◽

2021 ◽

Vol 503 (4) ◽

pp. 5274-5290

Author(s):

A K Sen ◽

V B Il’in ◽

M S Prokopjeva ◽

R Gupta

Keyword(s):

Magnetic Field ◽

Near Infrared ◽

Galactic Plane ◽

Photometric Data ◽

Dust Particles ◽

Dark Cloud ◽

Dark Clouds ◽

High Polarization ◽

Field Parallel ◽

Photometric Observations

ABSTRACT We present the results of our BVR-band photometric and R-band polarimetric observations of ∼40 stars in the periphery of the dark cloud CB54. From different photometric data, we estimate E(B − V) and E(J − H). After involving data from other sources, we discuss the extinction variations towards CB54. We reveal two main dust layers: a foreground, E(B − V) ≈ 0.1 mag, at ∼200 pc and an extended layer, $E(B-V) \gtrsim 0.3$ mag, at ∼1.5 kpc. CB54 belongs to the latter. Based on these results, we consider the reason for the random polarization map that we have observed for CB54. We find that the foreground is characterized by low polarization ($P \lesssim 0.5$ per cent) and a magnetic field parallel to the Galactic plane. The extended layer shows high polarization (P up to 5–7 per cent). We suggest that the field in this layer is nearly perpendicular to the Galactic plane and both layers are essentially inhomogeneous. This allows us to explain the randomness of polarization vectors around CB54 generally. The data – primarily observed by us in this work for CB54, by A. K. Sen and colleagues in previous works for three dark clouds CB3, CB25 and CB39, and by other authors for a region including the B1 cloud – are analysed to explore any correlation between polarization, the near-infrared, E(J − H), and optical, E(B − V), excesses, and the distance to the background stars. If polarization and extinction are caused by the same set of dust particles, we should expect good correlations. However, we find that, for all the clouds, the correlations are not strong.

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Effects of a Vertical Magnetic Field on Particle Confinement in a Magnetized Plasma Torus

Physical Review Letters ◽

10.1103/physrevlett.93.165003 ◽

2004 ◽

Vol 93 (16) ◽

Cited By ~ 39

Author(s):

S. H. Müller ◽

A. Fasoli ◽

B. Labit ◽

M. McGrath ◽

M. Podestà ◽

...

Keyword(s):

Magnetic Field ◽

Magnetized Plasma ◽

Vertical Magnetic Field ◽

Plasma Torus ◽

Particle Confinement

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Effects of repeated interactions and correlational disintegration on kinetic and transport properties of a non-neutral plasma in strong fields

Journal of Plasma Physics ◽

10.1017/s0022377800015087 ◽

1990 ◽

Vol 44 (1) ◽

pp. 167-190 ◽

Cited By ~ 1

Author(s):

Alf H. Øien

Keyword(s):

Magnetic Field ◽

Particle Transport ◽

Axial Magnetic Field ◽

Debye Length ◽

Electron Plasma ◽

Larmor Radius ◽

Equilibration Time ◽

Cylindrically Symmetric ◽

Electric Potentials ◽

Good Agreement

Collisions in a cylindrically symmetric non-neutral (electron) plasma, where the Larmor radius is much smaller than the Debye length, and the consequent particle transport, are studied. The plasma is confined radially by a strong axial magnetic field and axially by electric potentials. Hence two particles may interact repeatedly. Eventually they drift too far away from each other poloidally to interact any more, owing to shear in the E × B drift. The consequent build-up of correlation is limited by correlational disintegration due to collisions with ‘third particles’ between the repeated interactions. A kinetic equation including these effects is derived, and the cross-field particle transport along the density gradient is found. An associated equilibration time is shown to scale as B and to be in good agreement with the experimentally obtained values of Briscoli, Malmberg and Fine.

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Numerical Simulation of the Time Evolution of Small-Scale Irregularities in the F-Layer Ionospheric Plasma

International Journal of Geophysics ◽

10.1155/2011/353640 ◽

2011 ◽

Vol 2011 ◽

pp. 1-8 ◽

Cited By ~ 2

Author(s):

O. V. Mingalev ◽

G. I. Mingaleva ◽

M. N. Melnik ◽

V. S. Mingalev

Keyword(s):

Magnetic Field ◽

Time Evolution ◽

Ionospheric Plasma ◽

Debye Length ◽

Small Scale ◽

System Of Equations ◽

Applied Model ◽

Positive Ions ◽

F Region ◽

Small Scale Irregularity

Dynamics of magnetic field-aligned small-scale irregularities in the electron concentration, existing in the F-layer ionospheric plasma, is investigated with the help of a mathematical model. The plasma is assumed to be a rarefied compound consisting of electrons and positive ions and being in a strong, external magnetic field. In the applied model, kinetic processes in the plasma are simulated by using the Vlasov-Poisson system of equations. The system of equations is numerically solved applying a macroparticle method. The time evolution of a plasma irregularity, having initial cross-section dimension commensurable with a Debye length, is simulated during the period sufficient for the irregularity to decay completely. The results of simulation indicate that the small-scale irregularity, created initially in the F-region ionosphere, decays accomplishing periodic damped vibrations, with the process being collisionless.

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