Magnetohydrodynamic waves in a non-uniform current-carrying plasma column

An effect of an axial current on the propagation of low-frequency axisymmetric magnetohydroclynamic waves in a radially non-uniform plasma column was investigated theoretically and experimentally. It was found that the axial current and the density gradient cause a coupling between the torsional and compressional waves.

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Magneto-acoustic resonance in a non-uniform current carrying plasma column

Journal of Plasma Physics ◽

10.1017/s0022377800006322 ◽

1971 ◽

Vol 6 (3) ◽

pp. 607-614 ◽

Cited By ~ 5

Author(s):

J. Vaclavik

Keyword(s):

Magnetic Field ◽

Plasma Column ◽

Mass Density ◽

Acoustic Resonance ◽

Acoustic Oscillations ◽

Resonant Character ◽

Uniform Current ◽

Oscillating Magnetic Field ◽

Uniform Plasma

The forced radial magneto-acoustic oscillations in a plasma column with nonuniform mass density and temperature are investigated. It turns out that the oscillations have a resonant character similar to that of the magneto-acoustic oscillations in a uniform plasma column. The properties of the axial and azimuthal components of the oscillating magnetic field are discussed in detail.

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Magnetoacoustic oscillations in a finite-beta current carrying plasma column

Journal of Plasma Physics ◽

10.1017/s0022377800010060 ◽

1979 ◽

Vol 22 (2) ◽

pp. 223-229 ◽

Cited By ~ 3

Author(s):

M. L. Sawley

Keyword(s):

Magnetic Field ◽

Plasma Column ◽

Axial Current ◽

Numerical Calculations ◽

Axial Component ◽

Azimuthal Component ◽

Equilibrium Configurations ◽

Uniform Current ◽

Oscillating Magnetic Field

Forced magnetoacoustic oscillations in a fully ionized, non-uniform, current carrying plasma column of finite beta are treated theoretically. The results of numerical calculations are given for the specific case of diffuse pinch equilibrium configurations. It is found that, for these configurations, the amplitude of the axial component of the oscillating magnetic field is enhanced and the frequency at which magnetoacoustic resonance occurs is raised. It is also found that the presence of an equilibrium axial current produces a substantial azimuthal component, in addition to the axial component, of the oscillating magnetic field.

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m=0,±1 low frequency fast Alfven modes of a plasma column loaded in a sheath helix

Plasma Physics and Controlled Fusion ◽

10.1088/0741-3335/29/6/004 ◽

1987 ◽

Vol 29 (6) ◽

pp. 729-741 ◽

Cited By ~ 1

Author(s):

A Ganguli ◽

R Baskaran

Keyword(s):

Plasma Column ◽

Low Frequency

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Delineating a cased borehole in unconsolidated formations using dipole acoustic data from a nearby well

Geophysics ◽

10.1190/geo2020-0570.1 ◽

2021 ◽

pp. 1-39

Author(s):

Gu Xihao ◽

Xiao-Ming Tang ◽

Yuan-Da Su

Keyword(s):

Shear Waves ◽

Low Frequency ◽

Well Being ◽

Compressional Wave ◽

Acoustic Imaging ◽

Wave Radiation ◽

Dipole Source ◽

Compressional Waves ◽

Single Well ◽

Cased Borehole

A potential application for single-well acoustic imaging is the detection of an existing cased borehole in the vicinity of the well being drilled, which is important for drilling toward (when drilling a relief well), or away from (collision prevention), the existing borehole. To fulfill this application in the unconsolidated formation of shallow sediments, we propose a detection method using the low-frequency compressional waves from dipole acoustic logging. For this application, we perform theoretical analyses on elastic wave scattering from the cased borehole and derive the analytical expressions for the scattered wavefield for the incidence of compressional and shear waves from a borehole dipole source. The analytical solution, in conjunction with the elastic reciprocity theorem, provides a fast algorithm for modeling the whole process of wave radiation, scattering, and reception for the borehole acoustic detection problem. The analytical results agree well with those from 3D finite-difference simulations. The results show that compressional waves, instead of shear waves as commonly used for dipole acoustic imaging, are particularly advantageous for the borehole detection in the unconsolidated formation. Field data examples are used to demonstrate the application in a shallow marine environment, where dipole-compressional wave data in the measurement well successfully delineate a nearby cased borehole, validating our analysis results and application.

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Vertical to Horizontal Spectral Ratio (VHSR) Response of Seismic Wave Propagation in a Homogeneous Elastic – Poroelastic Medium Using The Spectral Finite Element Method

INDONESIAN JOURNAL OF APPLIED PHYSICS ◽

10.13057/ijap.v11i1.45969 ◽

2021 ◽

Vol 11 (1) ◽

pp. 95

Author(s):

Sudarmaji Saroji ◽

Budi Eka Nurcahya ◽

Nivan Ramadhan Sugiantoro

Keyword(s):

Finite Element Method ◽

Elastic Medium ◽

Seismic Waves ◽

Low Frequency ◽

Seismic Wave Propagation ◽

P Wave ◽

Poroelastic Medium ◽

Compressional Waves ◽

Spectral Finite Element Method ◽

Spectral Finite Element

<p>Numerical modeling of 2D seismic wave propagation using spectral finite element method to estimate the response of seismic waves passing through the poroelastic medium from a hydrocarbon reservoir has been carried out. A hybrid simple model of the elastic - poroelastic - elastic with a mesoscopic scale element size of about 50cm was created. Seismic waves which was in the form of the ricker function are generated on the first elastic medium, propagated into the poroelastic medium and then transmitted to the second elastic medium. Pororoelastic medium is bearing hydrocarbon fluid in the form of gas, oil or water. Vertical and horizontal component of velocity seismograms are recorded on all mediums. Seismograms which are recorded in the poroelastic and second elastic medium show the existence of slow P compressional waves following fast P compressional waves that do not appear on the seismogram of the first elastic medium. The slow P wave is generated when the fast P wave enters the interface of the elastic - poroelastic boundary, propagated in the poroelastic medium and is transmited to the second elastic medium. The curves of Vertical to horizontal spectrum ratio (VHSR) which are observed from seismograms recorded in the poroelastic and the second elastic medium show that the peak of VHSR values at low frequency correlated with the fluid of poroelastic reservoir. The highest VHSR value at the low frequency which is recorded on the seismogram is above the 2.5 Hz frequency for reservoirs containing gas and oil in the second elastic medium, while for the medium containing water is the highest VHSR value is below the 2.5 Hz frequency.</p>

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Fast magnetic field penetration into low resistivity plasma

Journal of Plasma Physics ◽

10.1017/s0022377817000046 ◽

2017 ◽

Vol 83 (1) ◽

Author(s):

Amnon Fruchtman

Keyword(s):

Magnetic Field ◽

Energy Dissipation ◽

Electric Field ◽

Density Gradient ◽

Magnetic Energy ◽

Measured Velocity ◽

Magnetic Field Penetration ◽

The Magnetic Field ◽

Uniform Plasma ◽

Field Penetration

Penetration of a magnetic field into plasma that is faster than resistive diffusion can be induced by the Hall electric field in a non-uniform plasma. This mechanism explained successfully the measured velocity of the magnetic field penetration into pulsed plasmas. Major related issues have not yet been resolved. Such is the theoretically predicted, but so far not verified experimentally, high magnetic energy dissipation, as well as the correlation between the directions of the density gradient and of the field penetration.

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Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834876 ◽

2019 ◽

Vol 630 ◽

pp. A39 ◽

Cited By ~ 5

Author(s):

H. Breuillard ◽

P. Henri ◽

L. Bucciantini ◽

M. Volwerk ◽

T. Karlsson ◽

...

Keyword(s):

Magnetic Field ◽

Low Frequency ◽

Compressional Waves ◽

Weibel Instability ◽

Plasma Environment ◽

Background Magnetic Field ◽

Rosetta Mission ◽

Ion Waves ◽

Plasma Coupling

Using in situ measurements from different instruments on board the Rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67P/Churyumov-Gerasimenko. These waves are thought to be generated by a modified ion-Weibel instability that grows due to a beam of water ions created by water molecules that outgass from the comet. We take advantage of a cometary outburst event that occurred on 2016 February 19 to probe this generation mechanism. We analyze the 3D magnetic field waveforms to infer the properties of the magnetic oscillations of the cometary ion waves. They are observed in the typical frequency range (~50 mHz) before the cometary outburst, but at ~20 mHz during the outburst. They are also observed to be elliptically right-hand polarized and to propagate rather closely (~0−50°) to the background magnetic field. We also construct a density dataset with a high enough time resolution that allows us to study the plasma contribution to the ion cometary waves. The correlation between plasma and magnetic field variations associated with the waves indicates that they are mostly in phase before and during the outburst, which means that they are compressional waves. We therefore show that the measurements from multiple instruments are consistent with the modified ion-Weibel instability as the source of the singing comet wave activity. We also argue that the observed frequency of the singing comet waves could be a way to indirectly probe the strength of neutral plasma coupling in the 67P environment.

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Anomalous skin effect for a plasma column in a magnetic field

Journal of Plasma Physics ◽

10.1017/s0022377800007911 ◽

1973 ◽

Vol 10 (3) ◽

pp. 349-358 ◽

Cited By ~ 9

Author(s):

R. G. Storer ◽

C. Meaney

Keyword(s):

Magnetic Field ◽

Plasma Column ◽

Electron Density Distribution ◽

Skin Effect ◽

Axial Magnetic Field ◽

Complete Solution ◽

Low Frequency ◽

Anomalous Skin Effect ◽

Plasma Radius ◽

Cylindrical Plasma Column

The influence of a steady axial magnetic field on the anomalous penetration of low frequency electromagnetic fields into a cylindrical plasma column is investigated by considering a plasma with a Gaussian electron density distribution. For this model, a complete solution is obtained for Boltzmann's equation coupled to Maxwell's equations, and the fields calculated exactly. The results show dramatic changes of the internal fields for small changes of the applied magnetic field when the average Lamour radius of the electrons is of the order of the plasma radius.

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