scholarly journals Collisionless Damping of Fast and Ion?Cyclotron Surface Waves

1993 ◽  
Vol 46 (2) ◽  
pp. 271 ◽  
Author(s):  
GW Rowe
Keyword(s):  
Surface Waves ◽  
Short Wavelength ◽  
Mode Conversion ◽  
Low Frequency ◽  
Wave Mode ◽  
Alfven Wave ◽  
Field Boundary ◽  
First Order ◽  
Vacuum Interface ◽  
Ion Cyclotron

A recently developed general kinetic theory of surface waves is used to calculate the collisionless damping of low frequency fast and ion-cyclotron surface waves on a magnetised plasma-vacuum interface. In particular, the possibility of Cherenkov (Landau and transit-time magnetic) absorption by electrons is accounted for, assuming a bi-Maxwellian distribution of electrons in velocity space. It is shown that in general the surface waves are damped via mode conversion to a short-wavelength mode, such as the kinetic Alfven wave, which is subsequently Landau absorbed within the plasma. For high temperatures this short-wavelength mode can also be radiated into the plasma without being completely absorbed. It is also shown that the related ion-sound surface wave mode and instability identified by Alexandrov et al. (1984) are unphysical, and are the result of neglecting the gas pressure in the first-order magnetic field boundary condition.

scholarly journals Poroelastic property analysis of seismic low-frequency shadows associated with gas reservoirs

2020 ◽  
Vol 17 (3) ◽  
pp. 463-474
Author(s):  
Shengjie Li ◽  
Ying Rao
Keyword(s):  
Mode Conversion ◽  
Low Frequency ◽  
Simulation Method ◽  
Wave Mode ◽  
Pore Fluid ◽  
Fluid Distribution ◽  
Gas Reservoirs ◽  
Tight Sandstone ◽  
Reservoir Properties ◽  
Gas Bearing

Abstract Seismic low-frequency amplitude shadows have been widely used as a hydrocarbon indicator. This study investigates the effect of reservoir properties and seismic wave mode conversion on the characteristics of the low-frequency amplitude shadows in gas-bearing reservoirs. The target gas reservoirs are typically related to the lithology of tight sandstone with strong heterogeneity. Pore-fluid distribution within the reservoirs presents patchy saturation in the vertical and horizontal directions, and this patchy saturation easily induces low-frequency shadows beneath gas-bearing reservoirs. These low-frequency shadows are validated by using a poroelastic simulation method. The results of our field case-based study indicate that pore-fluid property, plus the thickness and heterogeneity of reservoirs are the key elements in the generation of low-frequency shadows. The results also indicate that the poroelastic simulation method can be used to effectively predict the spatial distribution of gas-bearing reservoirs, by directly verifying the low-frequency shadow phenomenon existing in the seismic data.

Finite-frequency surface waves on current sheets

1991 ◽  
Vol 45 (3) ◽  
pp. 389-406 ◽  
Author(s):  
K. P. Wessen ◽  
N. F. Cramer
Keyword(s):  
Magnetic Field ◽  
Dispersion Relation ◽  
Surface Waves ◽  
Cyclotron Frequency ◽  
Low Frequency ◽  
Dielectric Tensor ◽  
Magnetic Field Direction ◽  
Field Reversal ◽  
Ion Cyclotron ◽  
The Magnetic Field

The dispersion relation for low-frequency surface waves at a current sheet between two magnetized plasmas is derived using the cold-plasma dielectric tensor with finite ion-cyclotron frequency. The magnetic field direction is allowed to change discontinuously across the sheet, but the plasma density remains constant. The cyclotron frequency causes a splitting of the dispersion relation into a number of mode branches with frequencies both less than and greater than the ion-cyclotron frequency. The existence of these modes depends in particular upon the degree of magnetic field discontinuity and the direction of wave propagation in the sheet relative to the magnetic field directions. Sometimes two modes can exist for the same direction of propagation. The existence of modes undamped by Alfvén resonance absorption is predicted. Analytical solutions are obtained in the low-frequency and magnetic-field-reversal limits. The solutions are obtained numerically in the general case.

scholarly journals Alfvén Wave Mode Conversion in Pulsar Magnetospheres

2021 ◽  
Vol 908 (2) ◽  
pp. 176
Author(s):  
Yajie Yuan ◽  
Yuri Levin ◽  
Ashley Bransgrove ◽  
Alexander Philippov
Keyword(s):  
Mode Conversion ◽  
Wave Mode ◽  
Alfven Wave

scholarly journals Resonant absorption of Alfven Waves and the Associated Phenomenon of Magnetic Reconnection

1990 ◽  
Vol 142 ◽  
pp. 245-249
Author(s):  
C. Uberoi
Keyword(s):  
Surface Waves ◽  
Magnetic Reconnection ◽  
Low Frequency ◽  
Resonant Absorption ◽  
Magnetic Activity ◽  
Alfven Wave ◽  
Flux Transfer Events ◽  
Long Period ◽  
Magnetospheric Cusp ◽  
Zero Frequency

The mathematical analysis of the Alfven Wave equation in inhomogeneous magnetic fields which explain the resonance absorption of Alfven surface waves near a resonant layer can also be used to show that magnetic reconnection process can arise near the zero frequency resonant layer driven by very low frequency Alfven surface waves. The associated phenomena of resonant absorption and magnetic reconnection in inhomogeneous plasmas can explain the recent obsrevations of intense magnetic activity in the long period geomagnetic micropulsations range, at magnetospheric cusp latitudes, during the time of occurence of flux transfer events.

The parametric excitation of kinetic Alfvén waves by a magnetic pump

1981 ◽  
Vol 26 (2) ◽  
pp. 253-266 ◽  
Author(s):  
N. F. Cramer ◽  
I. J. Donnelly
Keyword(s):  
Finite Temperature ◽  
Acoustic Waves ◽  
Temperature Effects ◽  
Mode Conversion ◽  
Low Frequency ◽  
Alfven Waves ◽  
Alfven Wave ◽  
Alfvén Waves ◽  
Ion Acoustic Wave ◽  
Low Frequency Waves

The parametric decay of a magneto-acoustic pump wave into low-frequency waves modified by finite temperature effects is considered. The excited waves are the kinetic Alfvén wave and the ion-acoustic wave. The former wave plays an important role in linear heating schemes employing the mode conversion of magneto-acoustic waves at the Alfvén resonance. Here we calculate the parametric growth rates and pump thresholds for excitation of these waves. The main result is that finite temperature effects tend to reduce the growth rate of Alfvén waves.

Mode conversion to the kinetic Alfvén wave in low-frequency heating experiments in the TCA tokamak

1989 ◽  
Vol 63 (22) ◽  
pp. 2476-2479 ◽  
Author(s):  
H. Weisen ◽  
K. Appert ◽  
G. Borg ◽  
B. Joye ◽  
A. Knight ◽  
...  
Keyword(s):  
Mode Conversion ◽  
Low Frequency ◽  
Alfven Wave ◽  
Kinetic Alfvén Wave ◽  
Kinetic Alfven Wave ◽  
Frequency Heating

scholarly journals General Dispersion Relation for Surface Waves on a Plasma?Vacuum Interface: Application to Magnetised Plasmas

1992 ◽  
Vol 45 (1) ◽  
pp. 55 ◽  
Author(s):  
GW Rowe
Keyword(s):  
Dispersion Relation ◽  
General Theory ◽  
Surface Waves ◽  
Low Frequency ◽  
Surface Currents ◽  
Ion Plasma ◽  
Vacuum Interface ◽  
Slight Extension ◽  
Infinite Conductivity ◽  
General Dispersion

The general dispersion relation for electromagnetic surface waves on a plasma-vacuum interface, recently derived by Rowe (1991), is applied to the case of a cold magnetised plasma bounded by a vacuum. It is illustrated how the dispersion relation and the surface wave fields may be determined in practice, and some general results are given. It is remarked that a plasma of this type satisfies the consistency conditions which were derived for the general theory by Rowe. These general results are then used to reproduce the dispersion relation of Cramer and Donnelly (1983) for low frequency surface waves in an electron-ion plasma. This example illustrates the general principles of the theory. A major difference between the derivation in their paper and the calculation of this paper is that in the former the plasma was assumed to be infinitely conducting whereas here the plasma is strictly assumed to have finite conductivity.The transition to infinite conductivity, which involves a slight extension of the general theory to include surface currents, is thus also discussed.

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