We study the controversy about the proper determination of the electromagnetic energy-flux field in anisotropic materials, which has been revived due to the relatively recent experiments on negative refraction in meta...We study the controversy about the proper determination of the electromagnetic energy-flux field in anisotropic materials, which has been revived due to the relatively recent experiments on negative refraction in metamaterials. Rather than analyzing energy-balance arguments, we use a pragmatic approach inspired by geometrical optics, and compare the predictions on angles of refraction at a flat interface of two possible choices on the energy flux: and . We carry out this comparison for a monochromatic Gaussian beam propagating in an anisotropic non-dissipative anisotropic metamaterial, in which the spatial localization of the electromagnetic field allows a more natural assignment of directions, in contrast to the usual study of plane waves. We compare our approach with the formalism of geometrical optics, which we generalize and analyze numerically the consequences of either choice.展开更多
In this investigation effort, we eventually infer that the overall quadrapole pattern of B<sub>y</sub> deflections, in the vicinity of a source in the Earth’s magnetotail, is most likely due to field alig...In this investigation effort, we eventually infer that the overall quadrapole pattern of B<sub>y</sub> deflections, in the vicinity of a source in the Earth’s magnetotail, is most likely due to field aligned currents (FACs) and not to Hall currents associated with an X-type collisionless reconnection. This categorically expressed statement is based upon sufficient observational evidence tightly associated with our own suggested model and the preceded works of the same author. Using representative events measured by satellite, our main aim is to describe the nature of the fundamental mechanism determining the polarity of the B<sub>y</sub> deflections associated with intense earthward ionplasma flows. A major finding is that we either observe magnetic flux rope (MFR) like structures (that is, entities having all the morphological features of ropes; i.e., a dipolar signature of B<sub>z</sub> occurring simultaneously with peaked B<sub>y</sub> and B<sub>total</sub> deflections) or mere B<sub>y</sub> deflections, however, the sign for all these (B<sub>y</sub>deflections) is always determined by the satellite placement in north (positive) or south (negative) plasma sheet. Therefore, the MFR-like structures located earthward of the source are most likely pseudo-MFRs;there is neither a tubular topology nor an axial magnetic field, the B<sub>y</sub> deflections are produced by FACs. According to the presented model, a fundamental concept is that both ions and electrons are simultaneously accelerated at the source site;in turn, the earthward streaming electrons (ions) form a bifurcated electron (ion) FAC just outside the electron diffusion region-EDR (IDR). In this way, inside the IDR (and earthward of the source) positive (negative) B<sub>y</sub> deflections in north (south) plasma sheet (PS) are produced due to FACs, and not to (inward) Hall currents as in the context of an X-line. Moreover, the ions form an “ion jet” within the IDR, while just outside this region they produce positive (negative) B<sub>y</sub> deflections in north (south) PS caused by ion FACs. The ion jet in the IDR is enveloped by the bifurcated electron FAC. Eventually, although the resulting pattern of B<sub>y</sub> deflections, due to both electron and ion FACs, is apparently the same with that resulting from Hall currents (in the X-line model), the underlying natural processes are, however, radically different. Certainly, the dominant “spatial entity” within the IDR is the ion jet-current (and not the Hall-electron current). Additional implications of the ion jets are also discussed.展开更多
Kinetic Alfvén waves(KAWs),with a strong parallel disturbed electric field,play an important role in energy transport and particle acceleration in the magnetotail.On the basis of high-resolution observations of t...Kinetic Alfvén waves(KAWs),with a strong parallel disturbed electric field,play an important role in energy transport and particle acceleration in the magnetotail.On the basis of high-resolution observations of the Magnetospheric Multiscale(MMS)Mission,we present a detailed description of the acceleration process of electrons by KAWs in the plasma sheet boundary layer(PSBL).The MMS observed strong electromagnetic disturbances carrying a parallel disturbed electric field with an amplitude of up to 8 mV/m.The measured ratio of the electric to magnetic field perturbations was larger than the local Alfvén speed and was enhanced as the frequency increased,consistent with the theoretical predictions for KAWs.This evidence indicates that the electromagnetic disturbances should be identified as KAWs.During the KAWs,the energy flux of electrons at energies above 1 keV in the parallel and anti-parallel directions are significantly enhanced,implying occurrences of electron beams at higher energies.Additionally,the KAWs became more electrostaticlike and filled with high-frequency ion acoustic waves.The energy enhancement of electron beams is in accordance with the derived work done with the observed parallel disturbed electric field of KAWs,indicating electron acceleration caused by KAWs.Therefore,these results provide direct evidence of electron acceleration by KAWs embodying electrostatic ion acoustic waves in the PSBL.展开更多
文摘We study the controversy about the proper determination of the electromagnetic energy-flux field in anisotropic materials, which has been revived due to the relatively recent experiments on negative refraction in metamaterials. Rather than analyzing energy-balance arguments, we use a pragmatic approach inspired by geometrical optics, and compare the predictions on angles of refraction at a flat interface of two possible choices on the energy flux: and . We carry out this comparison for a monochromatic Gaussian beam propagating in an anisotropic non-dissipative anisotropic metamaterial, in which the spatial localization of the electromagnetic field allows a more natural assignment of directions, in contrast to the usual study of plane waves. We compare our approach with the formalism of geometrical optics, which we generalize and analyze numerically the consequences of either choice.
文摘In this investigation effort, we eventually infer that the overall quadrapole pattern of B<sub>y</sub> deflections, in the vicinity of a source in the Earth’s magnetotail, is most likely due to field aligned currents (FACs) and not to Hall currents associated with an X-type collisionless reconnection. This categorically expressed statement is based upon sufficient observational evidence tightly associated with our own suggested model and the preceded works of the same author. Using representative events measured by satellite, our main aim is to describe the nature of the fundamental mechanism determining the polarity of the B<sub>y</sub> deflections associated with intense earthward ionplasma flows. A major finding is that we either observe magnetic flux rope (MFR) like structures (that is, entities having all the morphological features of ropes; i.e., a dipolar signature of B<sub>z</sub> occurring simultaneously with peaked B<sub>y</sub> and B<sub>total</sub> deflections) or mere B<sub>y</sub> deflections, however, the sign for all these (B<sub>y</sub>deflections) is always determined by the satellite placement in north (positive) or south (negative) plasma sheet. Therefore, the MFR-like structures located earthward of the source are most likely pseudo-MFRs;there is neither a tubular topology nor an axial magnetic field, the B<sub>y</sub> deflections are produced by FACs. According to the presented model, a fundamental concept is that both ions and electrons are simultaneously accelerated at the source site;in turn, the earthward streaming electrons (ions) form a bifurcated electron (ion) FAC just outside the electron diffusion region-EDR (IDR). In this way, inside the IDR (and earthward of the source) positive (negative) B<sub>y</sub> deflections in north (south) plasma sheet (PS) are produced due to FACs, and not to (inward) Hall currents as in the context of an X-line. Moreover, the ions form an “ion jet” within the IDR, while just outside this region they produce positive (negative) B<sub>y</sub> deflections in north (south) PS caused by ion FACs. The ion jet in the IDR is enveloped by the bifurcated electron FAC. Eventually, although the resulting pattern of B<sub>y</sub> deflections, due to both electron and ion FACs, is apparently the same with that resulting from Hall currents (in the X-line model), the underlying natural processes are, however, radically different. Certainly, the dominant “spatial entity” within the IDR is the ion jet-current (and not the Hall-electron current). Additional implications of the ion jets are also discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.41925018,41874194).
文摘Kinetic Alfvén waves(KAWs),with a strong parallel disturbed electric field,play an important role in energy transport and particle acceleration in the magnetotail.On the basis of high-resolution observations of the Magnetospheric Multiscale(MMS)Mission,we present a detailed description of the acceleration process of electrons by KAWs in the plasma sheet boundary layer(PSBL).The MMS observed strong electromagnetic disturbances carrying a parallel disturbed electric field with an amplitude of up to 8 mV/m.The measured ratio of the electric to magnetic field perturbations was larger than the local Alfvén speed and was enhanced as the frequency increased,consistent with the theoretical predictions for KAWs.This evidence indicates that the electromagnetic disturbances should be identified as KAWs.During the KAWs,the energy flux of electrons at energies above 1 keV in the parallel and anti-parallel directions are significantly enhanced,implying occurrences of electron beams at higher energies.Additionally,the KAWs became more electrostaticlike and filled with high-frequency ion acoustic waves.The energy enhancement of electron beams is in accordance with the derived work done with the observed parallel disturbed electric field of KAWs,indicating electron acceleration caused by KAWs.Therefore,these results provide direct evidence of electron acceleration by KAWs embodying electrostatic ion acoustic waves in the PSBL.
