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Simulations of the generation of energetic electrons and the formation of descending artificial plasma layers during HF‐heating at Arecibo
摘要： HF-induced Descending Artificial Plasma Layers (DAPLs) are artificially ionized plasma layers with plasma density in excess of that of the F2-peak. They were discovered during HF heating experiments at HAARP where they descended up to 70 km from the initial O mode wave reflection height. The DAPLs were attributed to the ionization of the neutral gas by high-energy electrons accelerated by the artificial ionospheric turbulence. Recently, DAPL formation was reported during the HF-heating experiment at Arecibo [Bernhardt et al., 2017]. This result was unexpected since Arecibo has the Effective Radiated Power (ERP) 4 – 5 times lower than that at HAARP, and since the experiment at Arecibo also has an unfavorable geometry, where the HF beam is directed vertically while the inclination of the geomagnetic field is 43.5o, allowing the fast electrons to escape the volume where their interaction with the artificial plasma turbulence occurs. However, the presence of photoelectrons due to the UV radiation from the Sun at the low latitude of Arecibo could magnify the flux of hot electrons. A model of artificial plasma layers created by the Arecibo HF facility is presented. It shows that Langmuir turbulence due to the HF heating can accelerate part of the ambient photoelectrons to energies above the ionization threshold of the neutral gas, leading to the formation of DAPLs. The present model results are in quantitative agreement with the experiments of Bernhardt et al. [2017].
关键词： HAARP,HF heating experiments,photoelectrons,HF-induced Descending Artificial Plasma Layers,Arecibo,Langmuir turbulence,DAPLs
更新于2025-09-04 15:30:14
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Effects of anisotropic oceanic turbulence on the propagation of the OAM mode of a partially coherent modified Bessel correlated vortex beam
摘要： We have studied the impacts of anisotropic turbulence on the orbital angular momentum (OAM) mode of a partially coherent modified Bessel correlated vortex beam propagation in an oceanic channel. In the weak turbulence paraxial channel, a new model of the probability density of OAM modes has been established. Effects of specific parameters of the oceanic turbulence on it have been studied, it is shown that there is an optimizing receiving aperture diameter in the specific interval of the ratio of temperature and salinity (cid:2) , which can reduce the effect of (cid:2) on the normalized energy weight of OAM modes and the reception of fluctuation signal. The effect of oceanic turbulence with higher anisotropy on the OAM signal is weaker than the turbulence possessing lower anisotropy. We can choose the mode carrying lower OAM quantum number to transfer information more efficiently, and we can utilize the OAM mode with large energy level difference between modes and so on to reduce mode interference and enhance the information capacity of optical communication links.
关键词： optical communication,partially coherent modified Bessel correlated vortex beam,propagation,OAM mode,anisotropic oceanic turbulence
更新于2025-09-04 15:30:14
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Turbulence-induced optical loss and cross-talk in spatial-mode multiplexed or single-mode free-space communication channels
摘要： Single-mode or mode multiplexed free-space atmospheric optical channels have drawn increasingly more attention in the past decade. The scope of their possible applications spans from the compatibility with the telecom WDM technology, fiber amplifiers, and modal multiplexing for increasing the channel throughput to various quantum communication related primitives such as entanglement distribution, high-dimensional spatially encoded quantum key distribution, and relativistic quantum cryptography. Many research papers discuss application of specific mode sets, such as optical angular momentum modes, for communication in the presence of atmospheric turbulence. At the same time some basic properties and key relations for such channels exposed to the atmospheric turbulence have not been derived yet. In the current paper we present simple analytic expressions and a general framework for assessing probability density functions of channel transmittance as well as modal cross-talk coefficients. Under some basic assumptions the presented results can be directly used for estimation of the Fried parameter of the turbulent channel based on the measured statistics of the fundamental mode transmittance coefficient.
关键词： free-space optical communication,single-mode channels,spatial-mode multiplexing,atmospheric turbulence,quantum communication
更新于2025-09-04 15:30:14
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Lidar arc scan uncertainty reduction through scanning geometry optimization
摘要： Doppler lidars are frequently operated in a mode referred to as arc scans, wherein the lidar beam scans across a sector with a ?xed elevation angle and the resulting measurements are used to derive an estimate of the n minute horizontal mean wind velocity (speed and direction). Previous studies have shown that the uncertainty in the measured wind speed originates from turbulent wind ?uctuations and depends on the scan geometry (the arc span and the arc orientation). This paper is designed to provide guidance on optimal scan geometries for two key applications in the wind energy industry: wind turbine power performance analysis and annual energy production prediction. We present a quantitative analysis of the retrieved wind speed uncertainty derived using a theoretical model with the assumption of isotropic and frozen turbulence, and observations from three sites that are onshore with ?at terrain, onshore with complex terrain and offshore, respectively. The results from both the theoretical model and observations show that the uncertainty is scaled with the turbulence intensity such that the relative standard error on the 10 min mean wind speed is about 30 % of the turbulence intensity. The uncertainty in both retrieved wind speeds and derived wind energy production estimates can be reduced by aligning lidar beams with the dominant wind direction, increasing the arc span and lowering the number of beams per arc scan. Large arc spans should be used at sites with high turbulence intensity and/or large wind direction variation.
关键词： arc scans,wind energy,Doppler lidar,scan geometry optimization,turbulence intensity
更新于2025-09-04 15:30:14