A Fourier-space description of oscillations in an inhomogeneous plasma. Part 1. Continuous Fourier transformation

1994 ◽  
Vol 52 (2) ◽  
pp. 245-264 ◽  
Author(s):  
Z. Sedláček ◽  
P. S. Cally
Keyword(s):  
Inhomogeneous Plasma ◽  
Fourier Space ◽  
Mixing Processes ◽  
Phase Mixing ◽  
Scattering States ◽  
Cold Plasmas ◽  
Dispersive Propagation ◽  
Stationary Scattering ◽  
Space Description ◽  
Generalized Wave Equation

Oscillations in inhomogeneous cold plasmas or inhomogeneous magnetofluids are interpreted in terms of the dynamics of their spectra in wavenumber space. By Fourier transforming the basic integro-differential equation of the problem, a generalized wave equation in wavenumber space is derived, thus converting the oscillation and phase-mixing processes in the original χ space into processes of dispersive propagation and scattering of the spectrum in wavenumber space. The Barston singular continuum eigenmodes correspond to stationary scattering states of a monochromatic wave in wavenumber space, whereas the damping phenomena in χ space correspond to transient ‘leaking’ phenomena accompanying scattering and dispersive propagation of a wave packet in wavenumber space.

A Fourier-space description of oscillations in an inhomogeneous plasma. Part 2. Discrete approach

1994 ◽  
Vol 52 (2) ◽  
pp. 265-296 ◽  
Author(s):  
P. S. Cally ◽  
Z. Sedláček
Keyword(s):  
Inhomogeneous Plasma ◽  
Fourier Space ◽  
Energy Propagation ◽  
Phase Mixing ◽  
Periodic Inhomogeneity ◽  
Discrete Approach ◽  
Natural Context ◽  
Almost Everywhere ◽  
Cold Plasmas ◽  
Space Description

The process of phase mixing in inhomogeneous MHD or cold plasmas is interpreted as one of energy propagation in discrete Fourier space. Three instructive scenarios are examined: (i) an isolated inhomogeneity with zero boundary conditions; (ii) a periodic inhomogeneity; and (iii) a monotonic inhomogeneity sandwiched between two semi-infinite uniform regions. In each case the coefficients of the associated wave equation in Fourier space for an appropriately chosen dependent variable are very nearly constant almost everywhere, so the propagation is like that of a free unreflected wave. An exception may arise in the coupling of the lowest modes, which can be highly reflective. It is argued that Fourier space is the simplest and most natural context in which to discuss the development of fine-scale oscillations.

MHD surface waves in high- and low-beta plasmas. Part 1. Normal-mode solutions

1989 ◽  
Vol 42 (1) ◽  
pp. 75-89 ◽  
Author(s):  
Z. E. Musielak ◽  
S. T. Suess
Keyword(s):  
Magnetic Field ◽  
Surface Waves ◽  
Normal Mode ◽  
General Structure ◽  
Normal Modes ◽  
Resonant Absorption ◽  
Normal Surface ◽  
Phase Mixing ◽  
Cold Plasmas ◽  
The Waves

Since the first paper by Barston (1964) on electrostatic oscillations in inhomogeneous cold plasmas, it has been commonly accepted that all finite layers with a continuous profile in pressure, density and magnetic field cannot support normal surface waves but instead the waves always decay through phase mixing (also called resonant absorption). Here we reanalyse the problem by studying a compressible current sheet of a general structure with rotation of the magnetic field included. We find that all inhomogeneous layers considered in the high-β plasma limit do not support normal modes. However, in the limit of a low-β plasma there are some cases when normal-mode solutions are recovered. The latter means that the process of resonant absorption is not common for all inhomogeneous layers.

scholarly journals Formation of Ultramylonites in an Upper Mantle Shear Zone, Erro-Tobbio, Italy

Minerals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1036
Author(s):  
Jolien Linckens ◽  
Sören Tholen
Keyword(s):  
Grain Size ◽  
Shear Zone ◽  
Upper Mantle ◽  
Microstructural Analysis ◽  
Shear Zones ◽  
Geodynamic Setting ◽  
Mixing Processes ◽  
Phase Mixing ◽  
Fine Grained ◽  
Order Of Magnitude

Deformation in the upper mantle is localized in shear zones. In order to localize strain, weakening has to occur, which can be achieved by a reduction in grain size. In order for grains to remain small and preserve shear zones, phases have to mix. Phase mixing leads to dragging or pinning of grain boundaries which slows down or halts grain growth. Multiple phase mixing processes have been suggested to be important during shear zone evolution. The importance of a phase mixing process depends on the geodynamic setting. This study presents detailed microstructural analysis of spinel bearing shear zones from the Erro-Tobbio peridotite (Italy) that formed during pre-alpine rifting. The first stage of deformation occurred under melt-free conditions, during which clinopyroxene and olivine porphyroclasts dynamically recrystallized. With ongoing extension, silica-undersaturated melt percolated through the shear zones and reacted with the clinopyroxene neoblasts, forming olivine–clinopyroxene layers. Furthermore, the melt reacted with orthopyroxene porphyroclasts, forming fine-grained polymineralic layers (ultramylonites) adjacent to the porphyroclasts. Strain rates in these layers are estimated to be about an order of magnitude faster than within the olivine-rich matrix. This study demonstrates the importance of melt-rock reactions for grain size reduction, phase mixing and strain localization in these shear zones.

Completeness of stationary scattering states. II

Physica ◽  
1955 ◽  
Vol 21 (6-10) ◽  
pp. 579-588
Author(s):  
N.G. Van Kampen
Keyword(s):  
Scattering States ◽  
Stationary Scattering

Completeness of stationary scattering states. I

Physica ◽  
1954 ◽  
Vol 21 (1-5) ◽  
pp. 127-136 ◽  
Author(s):  
N.G. Van Kampen
Keyword(s):  
Scattering States ◽  
Stationary Scattering

Phase-mixing of large amplitude electron oscillations in a cold inhomogeneous plasma

2018 ◽  
Vol 25 (2) ◽  
pp. 022102 ◽  
Author(s):  
Mithun Karmakar ◽  
Chandan Maity ◽  
Nikhil Chakrabarti ◽  
Sudip Sengupta
Keyword(s):  
Large Amplitude ◽  
Inhomogeneous Plasma ◽  
Phase Mixing

Inverse mirror plasma experimental device (IMPED) – a magnetized linear plasma device for wave studies

2014 ◽  
Vol 81 (2) ◽  
Author(s):  
Sayak Bose ◽  
P. K. Chattopadhyay ◽  
J. Ghosh ◽  
S. Sengupta ◽  
Y. C. Saxena ◽  
...  
Keyword(s):  
Axial Magnetic Field ◽  
Plasma Oscillation ◽  
Plasma Heating ◽  
Inhomogeneous Plasma ◽  
Maximum Amplitude ◽  
Experimental Device ◽  
Phase Mixing ◽  
New Device ◽  
Plasma Device ◽  
Collective Oscillations

In a quasineutral plasma, electrons undergo collective oscillations, known as plasma oscillations, when perturbed locally. The oscillations propagate due to finite temperature effects. However, the wave can lose the phase coherence between constituting oscillators in an inhomogeneous plasma (phase mixing) because of the dependence of plasma oscillation frequency on plasma density. The longitudinal electric field associated with the wave may be used to accelerate electrons to high energies by exciting large amplitude wave. However when the maximum amplitude of the wave is reached that plasma can sustain, the wave breaks. The phenomena of wave breaking and phase mixing have applications in plasma heating and particle acceleration. For detailed experimental investigation of these phenomena a new device, inverse mirror plasma experimental device (IMPED), has been designed and fabricated. The detailed considerations taken before designing the device, so that different aspects of these phenomena can be studied in a controlled manner, are described. Specifications of different components of the IMPED machine and their flexibility aspects in upgrading, if necessary, are discussed. Initial results meeting the prerequisite condition of the plasma for such study, such as a quiescent, collisionless and uniform plasma, are presented. The machine produces δnnoise/n⩽ 1%,Luniform~ 120 cm at argon filling pressure of ~10−4mbar and axial magnetic field ofB= 1090 G.

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