Engineering of fast mode conversion in multimode waveguides

2012 ◽  
Vol 37 (24) ◽  
pp. 5118 ◽  
Author(s):  
Shuo-Yen Tseng ◽  
Xi Chen
Keyword(s):  
Mode Conversion ◽  
Fast Mode ◽  
Multimode Waveguides

scholarly journals Mode conversion of two-fluid shocks in a partially-ionised, isothermal, stratified atmosphere

2020 ◽  
Vol 637 ◽  
pp. A97
Author(s):  
B. Snow ◽  
A. Hillier
Keyword(s):  
Solar Atmosphere ◽  
Mode Conversion ◽  
Frictional Heating ◽  
Fast Mode ◽  
Compressional Waves ◽  
Pressure Scale ◽  
Velocity Drift ◽  
Two Fluid ◽  
Lower Solar Atmosphere

Context. The plasma of the lower solar atmosphere consists of mostly neutral particles, whereas the upper solar atmosphere is mostly made up of ionised particles and electrons. A shock that propagates upwards in the solar atmosphere therefore undergoes a transition where the dominant fluid is either neutral or ionised. An upwards propagating shock also passes a point where the sound and Alfvén speed are equal. At this point the energy of the acoustic shock can separated into fast and slow components. The way the energy is distributed between the two modes depends on the angle of magnetic field. Aims. We aim to investigate the separation of neutral and ionised species in a gravitationally stratified atmosphere. The role of two-fluid effects on the structure of the shocks post-mode-conversion and the frictional heating is quantified for different levels of collisional coupling. Methods. Two-fluid numerical simulations were performed using the (PIP) code of a wave steepening into a shock in an isothermal, partially-ionised atmosphere. The collisional coefficient was varied to investigate the regimes where the plasma and neutral species are weakly, strongly, and finitely coupled. Results. The propagation speeds of the compressional waves hosted by neutral and ionised species vary and, therefore, velocity drift between the two species is produced as the plasma attempts to propagate faster than the neutrals. This is most extreme for a fast-mode shock. We find that the collisional coefficient drastically impacts the features present in the system, specifically the mode conversion height, type of shocks present, and the finite shock widths created by the two-fluid effects. In the finitely-coupled regime, fast-mode shock widths can exceed the pressure scale height, which may lead to a new potential observable of two-fluid effects in the lower solar atmosphere.

Numerical modelling of MHD waves in the solar chromosphere

2005 ◽  
Vol 364 (1839) ◽  
pp. 395-404 ◽  
Author(s):  
Mats Carlsson ◽  
Thomas J Bogdan
Keyword(s):  
Magnetic Field ◽  
Acoustic Waves ◽  
Mode Conversion ◽  
Three Dimensions ◽  
Mhd Waves ◽  
Solar Chromosphere ◽  
Fast Mode ◽  
Reflected Waves ◽  
The Waves ◽  
The Magnetic Field

Acoustic waves are generated by the convective motions in the solar convection zone. When propagating upwards into the chromosphere they reach the height where the sound speed equals the Alfvén speed and they undergo mode conversion, refraction and reflection. We use numerical simulations to study these processes in realistic configurations where the wavelength of the waves is similar to the length scales of the magnetic field. Even though this regime is outside the validity of previous analytic studies or studies using ray-tracing theory, we show that some of their basic results remain valid: the critical quantity for mode conversion is the angle between the magnetic field and the k-vector: the attack angle. At angles smaller than 30° much of the acoustic, fast mode from the photosphere is transmitted as an acoustic, slow mode propagating along the field lines. At larger angles, most of the energy is refracted/reflected and returns as a fast mode creating an interference pattern between the upward and downward propagating waves. In three-dimensions, this interference between waves at small angles creates patterns with large horizontal phase speeds, especially close to magnetic field concentrations. When damping from shock dissipation and radiation is taken into account, the waves in the low–mid chromosphere have mostly the character of upward propagating acoustic waves and it is only close to the reflecting layer we get similar amplitudes for the upward propagating and refracted/reflected waves. The oscillatory power is suppressed in magnetic field concentrations and enhanced in ring-formed patterns around them. The complex interference patterns caused by mode-conversion, refraction and reflection, even with simple incident waves and in simple magnetic field geometries, make direct inversion of observables exceedingly difficult. In a dynamic chromosphere it is doubtful if the determination of mean quantities is even meaningful.

Shortcut to Mode Conversion via Level Crossing in Engineered Multimode Waveguides

2014 ◽  
Vol 26 (2) ◽  
pp. 123-126 ◽  
Author(s):  
Chi-Shung Yeih ◽  
Hong-Xi Cao ◽  
Shuo-Yen Tseng
Keyword(s):  
Mode Conversion ◽  
Level Crossing ◽  
Multimode Waveguides

scholarly journals Mode conversion using optical analogy of shortcut to adiabatic passage in engineered multimode waveguides

2012 ◽  
Vol 20 (21) ◽  
pp. 24085 ◽  
Author(s):  
Tzung-Yi Lin ◽  
Fu-Chen Hsiao ◽  
Yao-Wun Jhang ◽  
Chieh Hu ◽  
Shuo-Yen Tseng
Keyword(s):  
Mode Conversion ◽  
Adiabatic Passage ◽  
Multimode Waveguides ◽  
Optical Analogy

Particle simulations of mode conversion between slow mode and fast mode in lower hybrid range of frequencies

2016 ◽  
Vol 23 (1) ◽  
pp. 012504 ◽  
Author(s):  
Guozhang Jia ◽  
Nong Xiang ◽  
Xueyi Wang ◽  
Yueheng Huang ◽  
Yu Lin
Keyword(s):  
Mode Conversion ◽  
Lower Hybrid ◽  
Fast Mode ◽  
Slow Mode ◽  
Particle Simulations
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