SCATTERING OF RADIO WAVES BY AN IONIZED GAS IN THERMAL EQUILIBRIUM

1960 ◽  
Vol 38 (8) ◽  
pp. 1114-1133 ◽  
Author(s):  
J. A. Fejer
Keyword(s):  
Incident Wave ◽  
Thermal Equilibrium ◽  
Debye Length ◽  
Density Fluctuations ◽  
Characteristic Scale ◽  
Radio Waves ◽  
Ionized Gas ◽  
Positive Ions ◽  
Frequency Power Spectrum ◽  
Frequency Power

A theory is developed for the scattering of radio waves by density fluctuations which exist in an ionized gas in thermal equilibrium.Expressions for the frequency power spectrum of the scattered waves are obtained. These expressions make it possible to interpret the results of observations of this type of scattering from the ionosphere in terms of electron density and temperature.It is shown that if the characteristic scale of the scattering irregularities (this scale depends on the wavelength of the incident radio wave and the scattering angle) is much greater than the Debye length then the width of the spectrum of the scattered signal is determined by the thermal velocities (and the collision frequencies if the latter are sufficiently high) of the positive ions, rather than of the electrons.If the characteristic scale is greater than the Debye length then for low collision frequencies the spectrum is flat-topped, with two slightly raised shoulders situated symmetrically above and below the frequency of the incident wave. For high collision frequencies the spectrum has only one maximum situated at the frequency of the incident wave.

SCATTERING OF RADIO WAVES BY AN IONIZED GAS IN THERMAL EQUILIBRIUM IN THE PRESENCE OF A UNIFORM MAGNETIC FIELD

1961 ◽  
Vol 39 (5) ◽  
pp. 716-740 ◽  
Author(s):  
J. A. Fejer
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Thermal Equilibrium ◽  
Uniform Magnetic Field ◽  
Debye Length ◽  
Density Fluctuations ◽  
Total Power ◽  
Radio Waves ◽  
Ionized Gas ◽  
The Magnetic Field

In an earlier paper (Fejer 1960) a theory was developed for the scattering of radio waves by the electron density fluctuations that exist in an ionized gas in thermal equilibrium. The theory treated only the extreme cases where the "characteristic scale" of the scattering irregularities is either very much larger or very much smaller than the Debye length. The presence of only one type of singly charged ion was considered and the ion and electron temperatures were assumed equal. The effects of an external magnetic field were not taken into account.These earlier limitations are removed in the present paper and the effects of an external magnetic field are taken into account.It is shown that the total power is independent of the magnetic field and an expression for the frequency spectrum of scattered power in the presence of a uniform magnetic field is obtained. Useful approximations to this expression are derived for various limiting cases of interest.It is concluded that the magnetic field need not be taken into account in the interpretation of past observations by Bowles (1958, 1959) and by Pineo, Kraft, and Briscoe (1960). In future experiments, however, particularly at great heights, the effect of the magnetic field could be considerable.

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

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
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.

A DIFFERENCE OF TIME-FREQUENCY POWER SPECTRUM DURING QRS IN Q FROM NON-Q WAVE MYOCARDIAL INFARCTION

2005 ◽  
Author(s):  
NAOKO ZENDA ◽  
TAKESHI TSUTSUMI ◽  
DAISUKE WAKATSUKI ◽  
FUMIKO YANAGISAWA ◽  
HISA SHIMOJIMA ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Power Spectrum ◽  
Time Frequency ◽  
Frequency Power Spectrum ◽  
Frequency Power ◽  
Q Wave

The Spacecraft Potential’s Influence on the FOV of Rosetta-ICA at Low Ion Energies

2020 ◽  
Author(s):  
Sofia Bergman ◽  
Gabriella Stenberg Wieser ◽  
Martin Wieser ◽  
Fredrik Johansson ◽  
Anders Eriksson
Keyword(s):  
Debye Length ◽  
Low Energy ◽  
In Situ Techniques ◽  
Positive Ions ◽  
Spacecraft Potential ◽  
Energy Part ◽  
Ion Energies ◽  
Low Energies ◽  
Composition Analyzer ◽  
Low Energy Ions

<p><span>Low-energy ions play important roles in many processes in the environments around various bodies in the solar system. At comets, they are, for example, important for the understanding of the interaction of the cometary particles with the solar wind, including the formation of the diamagnetic cavity. </span></p><p><span>Unfortunately, spacecraft charging makes low-energy ions difficult to measure using in-situ techniques. The charged spacecraft surface will attract or repel the ions prior to detection, affecting both their trajectories and energy. The affected trajectories will change the effective FOV of the instrument. A negatively charged spacecraft will focus incoming positive ions, enlarging and distorting the FOV.</span></p><p><span>We model the low-energy FOV distortion of the Ion Composition Analyzer (ICA) on board Rosetta. ICA is an ion spectrometer measuring positive ions with an energy range of a few eV to 40 keV. Rosetta was commonly charged to a negative potential throughout the mission, and consequently the positive ions were accelerated towards the spacecraft before detection. This distorted the low-energy part of the data. We use the Spacecraft Plasma Interaction Software (SPIS) to simulate the environment around the spacecraft and backtrace particles from the instrument. We then compare the travel direction of the ions at detection and infinity, and draw conclusions about the resulting FOV distortion. We investigate the distortion for different spacecraft potentials and Debye lengths of the surrounding plasma. </span></p><p> <span>The results show that the effective FOV of ICA is severely distorted at low energies, but the distortion varies between different viewing directions of the instrument. It is furthermore sensitive to changes in the Debye length and we observe a small non-linearity in the relation between FOV distortion, ion energy and spacecraft potential. Generally, the FOV is not significantly affected when the energy of the ions is above twice the spacecraft potential. </span></p>

scholarly journals Hyperbolic kernel for time-frequency power spectrum

2003 ◽  
Vol 42 (8) ◽  
pp. 2400 ◽  
Author(s):  
Khoa N. Le ◽  
Kishor P. Dabke ◽  
Gregory K. Egan
Keyword(s):  
Power Spectrum ◽  
Time Frequency ◽  
Frequency Power Spectrum ◽  
Frequency Power

Plasma Generation for Materials Processing

MRS Bulletin ◽  
1996 ◽  
Vol 21 (8) ◽  
pp. 32-37 ◽  
Author(s):  
M.A. Lieberman ◽  
G.S. Selwyn ◽  
M. Tuszewski
Keyword(s):  
Charged Particle ◽  
Thermal Equilibrium ◽  
Low Pressure ◽  
Materials Processing ◽  
Voltage Source ◽  
Plasma Discharges ◽  
Plasma Generation ◽  
Neutral Gas ◽  
Positive Ions ◽  
Weakly Ionized

Chemically reactive plasma discharges are widely used to process materials. A plasma is a primarily electrically neutral collection of free charged particles moving in random directions. The simplest plasma consists of electrons and one kind of positive ions. This article deals primarily with plasma discharges, which are plasmas having the following features:(1) They are driven electrically.(2) Charged-particle collisions with neutral-gas molecules are important.(3) There are boundaries at which surface losses are important.(4) Ionization of neutrals sustains the plasma in the steady state.One simple discharge consists of a voltage source that drives current through a low-pressure gas between two conducting plates or electrodes. The gas “breaks down” to form a plasma, usually weakly ionized—that is, the plasma density is only a small fraction of the neutral-gas density.The plasmas used in materials processing present an enormous range of charged-particle densities n and of temperatures Te, Ti, and T for electrons, ions, and processing gas, respectively. High-pressure (atmospheric) discharges are in near-thermal equilibrium (Te ~ Ti ~ T ~ 0.1–2 eV). Plasma temperatures are usually given in equivalent electron-volt units: One eV is equivalent to 11600 K through the Boltzmann constant. As discussed in the article by Boulos and Pfender in this issue of MRS Bulletin, these thermal discharges have high densities n ~ 1014-1019 particles/cm3 and are mainly used as heat sources. Low-pressure (1 mTorr–10 Torr) discharges are not in thermal equilibrium (Te ~ 2–5 eV ≫ Ti ~ T) and have low densities n ~ 109–1012 particles/cm3. As discussed in several of the following articles, these discharges are used as miniature chemical factories in which feedstock gases are broken into positive ions and chemically reactive etchants, deposition precursors, etc., which then flow to and physically or chemically react at the surface of a substrate.

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