scholarly journals Pc2-3 geomagnetic pulsations on the ground, in the ionosphere, and in the magnetosphere: MM100, CHAMP, and THEMIS observations

2015 ◽  
Vol 33 (1) ◽  
pp. 117-128 ◽  
Author(s):  
N. Yagova ◽  
B. Heilig ◽  
E. Fedorov
Keyword(s):  
Amplitude Ratio ◽  
Wave Transmission ◽  
Alfven Wave ◽  
Occurrence Rate ◽  
Full Wave ◽  
Quality Signals ◽  
Rate Maximum ◽  
L Value ◽  
Orbiting Spacecraft ◽  
Shear Alfven Waves

Abstract. We analyze Pc2-3 pulsations recorded by the CHAMP (CHAllenging Minisatellite Payload) satellite in the F layer of the Earth's ionosphere, on the ground, and in the magnetosphere during quiet geomagnetic conditions. The spectra of Pc2-3 pulsations recorded in the F layer are enriched with frequencies above 50 mHz in comparison to the ground Pc2-3 spectra. These frequencies are higher than the fundamental harmonics of the field line resonances in the magnetosphere. High quality signals with dominant frequencies 70–200 mHz are a regular phenomenon in the F layer and in the magnetosphere. The mean latitude of the maximum Pc2-3 occurrence rate lies at L ≈ 3.5 in the F layer, i.e., inside the plasmasphere. Day-to-day variations of the L value of the CHAMP Pc2-3 occurrence rate maximum follow the plasmapause day-to-day variations. Polarization and amplitude of Pc2-3s in the magnetosphere, in the ionosphere, and on the ground allow us to suggest that they are generated as fast magnetosonic (FMS) waves in the outer magnetosphere and are partly converted into shear Alfven waves near the plasmapause. The observed ground-to-ionosphere amplitude ratio during the night is interpreted as a result of the Alfven wave transmission through the ionosphere. The problem of wave transmission through the ionosphere is solved theoretically by means of a numerical solution of the full-wave equation for the Alfven wave reflection from and transmission through a horizontally stratified ionosphere. The best agreement between the calculated and measured values of the ground-to-ionosphere amplitude ratio is found for k = 5 × 10−3 km−1, i.e., the observed ground-to-ionosphere amplitude ratio corresponds to a wave spatial scale which could provide a Doppler shift within a few percent of the apparent frequency of the Pc2-3 pulsations as recorded by a low-orbiting spacecraft.

Compact filtering power dividers with wide upper stopband

2019 ◽  
Vol 11 (08) ◽  
pp. 765-773
Author(s):  
Gaoya Dong ◽  
Weimin Wang ◽  
Yuanan Liu
Keyword(s):  
Transmission Lines ◽  
Wave Transmission ◽  
Coupling Matrix ◽  
Power Dividers ◽  
Full Wave ◽  
Half Wave ◽  
Coupled Lines ◽  
Quarter Wave ◽  
Simulation Results ◽  
Good Agreement

AbstractA series of compact filtering power dividers (FPDs) with simple layouts are proposed based on coupling topology. The structure of the presented FPD1 is composed of three resonators and one isolating resistor. These FPDs can be designed based on coupling matrix filter theory. A half-wave transmission line is employed in FPD2 to introduce a transmission zero (TZ) locating at 1.27f0. The FPD3 is designed by replacing quarter-wave transmission lines in FPD2 with quarter-wave coupled lines, which will produce a TZ locating at 1.96 f0 and extend upper stopband bandwidth. For verification, three FPDs centered at 2.45 GHz are fabricated and measured. All measured results are in good agreement with the full-wave simulation results.

Alfven Wave Transmission and Heating of Solar Coronal Loops

1998 ◽  
Vol 499 (2) ◽  
pp. 945-950 ◽  
Author(s):  
C. Litwin ◽  
R. Rosner
Keyword(s):  
Wave Transmission ◽  
Alfven Wave ◽  
Coronal Loops ◽  
Solar Coronal

Hybrid magnetohydrodynamic–kinetic model of standing shear Alfvén waves

2003 ◽  
Vol 69 (4) ◽  
pp. 277-304 ◽  
Author(s):  
PETER A. DAMIANO ◽  
R. D. SYDORA ◽  
J. C. SAMSON
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Cold Plasma ◽  
Electron Distribution Function ◽  
Alfven Waves ◽  
Mhd Equations ◽  
Alfven Wave ◽  
Alfvén Waves ◽  
Model Parameters ◽  
Shear Alfven Waves

We have developed a hybrid magnetohydrodynamics (MHD) –kinetic box model valid for standing shear Alfvén waves using the cold plasma MHD equations coupled to a system of kinetic electrons. The guiding centre equations are used for the motion of the electrons and the system is closed via an expression for the field-aligned electric field in terms of the perpendicular electric field and moments of the electron distribution function. The perpendicular electric fields are derived from the ideal MHD approximation. We outline the basic model equations and method of solution. Simulations are then presented comparing the hybrid model results with a cold plasma MHD model. Landau damping is shown to heavily damp the standing shear Alfvén wave in the hybrid simulations when $v_{th} \ge V_{A}$. The damping rate is shown to be in good agreement with the theoretical rate calculated for the model parameters.

Alfven Wave Excitation in a Cavity with a Transverse Magnetic Field

1983 ◽  
Vol 38 (6) ◽  
pp. 616-624
Author(s):  
M. Bureš
Keyword(s):  
Magnetic Field ◽  
Transverse Magnetic ◽  
Alfven Wave ◽  
Wave Number ◽  
Mass Motion ◽  
Wave Excitation ◽  
Frequency Range ◽  
Poloidal Magnetic Field ◽  
Cavity Modes ◽  
Shear Alfven Waves

A transversely magnetized cylindrical plasma model with an internal rod conductor is used to approximate the FIVA internal ring device of Spherator type with a purely poloidal magnetic field. It is shown that an excitation asymmetry along the plasma column, i.e. with a wave number k2 ≠ 0, introduces a coupling between the magnetoacoustic and shear Alfven waves in the frequency range ω ≪ ωci. The introduction of an equilibrium mass motion along the plasma cylinder introduces a flow continuum. Simultaneously the Alfven resonance frequency becomes Doppler shifted. The experimental observations indicate that cavity modes do not build up in the FIVA device in the case of nonsymmetric excitation. If on the other hand the exciting structure becomes symmetric, i.e. with k2 = 0, the magnetoacoustic resonances become excited. The resulting Q values are rather low which indicates that the coupling to the shear wave through the Hall electric field cannot be neglected

Aspect-ratio dependence of Alfvén-wave current drive and its efficiency in simulated tokamak plasmas. A systematic, full-wave equation investigation

1998 ◽  
Vol 59 (3) ◽  
pp. 461-498 ◽  
Author(s):  
S. CUPERMAN ◽  
C. BRUMA ◽  
K. KOMOSHVILI
Keyword(s):  
Wave Equation ◽  
Aspect Ratio ◽  
Current Drive ◽  
Smooth Transition ◽  
Alfven Wave ◽  
Numerical Code ◽  
Ratio Dependence ◽  
Full Wave ◽  
Radial Profiles ◽  
Consistent Solution

We investigate theoretically the aspect-ratio dependence of Alfvén-wave current drive (AWCD) in ‘simulated’ tokamaks, in the range 1.1[les ]R/a[les ]10 (where R and a are the major and minor radii, respectively). The study is carried out within the framework of resistive MHD, and is based on the consistent solution of the full-wave equation (E∥≠0); both shear and simulated toroidicity effects are taken into account. The AWCD includes components due to (wave) momentum transfer, helicity injection and plasma flow. The aspect-ratio-dependent features investigated include the radial profiles as well as the integrated power absorption, current drive and efficiency; the effects of antenna parameters (wavenumbers and frequency) are also explored. The numerical code developed and used for these computations has been benchmarked with the aid of analytical solutions obtained for the antenna–metallic-wall system in vacuum, as well as by the smooth transition from the vacuum case to the actual plasma case. Results of extensive calculations for the so-called Alfvén-continuum frequency range are presented and discussed.

scholarly journals Propagation of shear Alfvén waves in a two-ion plasma and application as a diagnostic for the ion density ratio

2020 ◽  
Vol 86 (6) ◽  
Author(s):  
J. Robertson ◽  
T. A. Carter ◽  
S. Vincena
Keyword(s):  
Density Ratio ◽  
Cutoff Frequency ◽  
Diagnostic Technique ◽  
Alfven Waves ◽  
Alfven Wave ◽  
Larmor Radius ◽  
Alfvén Waves ◽  
Ion Density ◽  
Background Magnetic Field ◽  
Shear Alfven Waves

In this paper, we propose an efficient diagnostic technique for determining spatially resolved measurements of the ion density ratio in a magnetized two-ion species plasma. Shear Alfvén waves were injected into a mixed helium–neon plasma using a magnetic loop antenna, for frequencies spanning the ion cyclotron regime. Two distinct propagation bands are observed, bounded by $\omega < \varOmega _\textrm {Ne}$ and $\omega _{ii} < \omega < \varOmega _\textrm {He}$ , where $\omega _{ii}$ is the ion–ion hybrid cutoff frequency and $\varOmega _\textrm {He}$ and $\varOmega _\textrm {Ne}$ are the helium and neon cyclotron frequencies, respectively. A theoretical analysis of the cutoff frequency was performed and shows it to be largely unaffected by kinetic electron effects and collisionality, although it can deviate significantly from $\omega _{{ii}}$ in the presence of warm ions due to ion finite Larmor radius effects. A new diagnostic technique and accompanying algorithm was developed in which the measured parallel wavenumber $k_\parallel$ is numerically fit to the predicted inertial Alfvén wave dispersion in order to resolve the local ion density ratio. A major advantage of this algorithm is that it only requires a measurement of $k_\parallel$ and the background magnetic field in order to be employed. This diagnostic was tested on the Large Plasma Device at UCLA and was successful in yielding radially localized measurements of the ion density ratio.

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