Effects of polarization-reversed electromagnetic ion cyclotron waves on the ring current dynamics

Electromagnetic ion cyclotron(EMIC)waves are widely believed to play an important role in influencing the radiation belt and ring current dynamics.Most studies have investigated the effects or characteristics of EMIC waves by assuming their left-handed polarization.However,recent studies have found that the reversal of polarization,which occurs at higher latitudes along the wave propagation path,can change the wave-induced pitch angle diffusion coefficients.Whether such a polarization reversal can influence the global ring current dynamics remains unknown.In this study,we investigate the ring current dynamics and proton precipitation loss in association with polarization-reversed EMIC waves by using the ring current-atmosphere interactions model(RAM).The results indicate that the polarization reversal of H-band EMIC waves can truly decrease the scattering rates of protons of 10 to 50 keV or>100 keV in comparison with the scenario in which the EMIC waves are considered purely left-handed polarized.Additionally,the global ring current intensity and proton precipitation may be slightly affected by the polarization reversal,especially during prestorm time and the recovery phase,but the effects are not large during the main phase.This is probably because the H-band EMIC waves contribute to the proton scattering loss primarily at E<10 keV,an energy range that is not strongly affected by the polarization reversal.

Ray Tracing Study of Electromagnetic Ion Cyclotron Waves Associated with Bi-Ion Frequencies

Ray tracing study of electromagnetic ion cyclotron （EMIC） waves is conducted based on a realistic plasma density model. The simulation result shows that EMIC waves propagate away from the equatorial source region to higher latitudes basically along geomagnetic field lines, and are reflected at the region where their frequency matches the local bi-ion frequency. H＋ band suffers H＋-He＋ bi-ion frequency reflection at lower latitudes, whereas He＋ band suffers He＋-O＋ bi-ion frequency reflection at higher latitudes. Moreover, the concentration of heavy ions slightly affects the bi-ion frequencies and then slightly determines the reflection location of ray paths of EMIC waves. The current results present the first detailed study on the propagation characteristics of EMIC waves associated with bi-ion frequencies.

The Nonlinear Evolution of Ion Cyclotron Waves in the Earth's Magnetosheath

With one-dimensional （l-D） hybrid simulations we investigate the nonlinear evolu- tion of the ion cyclotron waves excited by the H＋ and He2＋ temperature anisotropies, and analyze the evolution by using the wavelet analysis method. The results show that the proton cyclotron waves with the dominant frequency higher than the helium gyro-frequency （ΩHe = 0.5Ωp, with Ωp and ΩHe the proton and helium gyro-frequencies respectively ） are firstly excited, and then the helium cyclotron waves with the dominant frequency lower than the helium gyro-frequency are excited. The relation of our simulation results to the BIF（bifurcated） （there are two peaks in the wave spectrum： one above and one below ΩHe） and CON（continuous） （continuous spectrum from 0.1 Ωp to 1.0 Ωp） wave spectra observed in the magnetosheath are discussed.

Nonadiabatic acceleration of plasma sheet ions related to ion cyclotron waves

The nonadiabatic acceleration of plasma sheet ions is important to the understanding of substorm energetic injections and the formation of ring current. Previous studies show that nonadiabatic acceleration of protons by magnetic field dipolarization is hard to occur at X>–10 RE because the time-scale of dipolarization(several minutes) is much larger than the gyroperiod of protons there(several seconds). In this paper, we present a case of nonadiabatic acceleration of plasma sheet ions observed by Cluster on October 30, 2006 at(XGSM, YGSM)=(-7.7, 4.7) RE. The nonadiabatic acceleration of ions is caused not by previously reported magnetospheric dipolarization but by the ultra low frequency(ULF) waves during magnetospheric dipolarization. The nonadiabatic acceleration of ions generates a new energy flux structure of ions, which is characterized by the usual energy flux increase of ions(28–80 ke V) and a concurrent energy flux decrease of ions in a lower energy range(10 e V–20 ke V). These new observations constitute a complete physical picture: The lower energy ions absorb the wave energy, and thus get accelerated to higher energy. We use a nonadiabatic model to interpret the ion energy flux variations. Both analytic and simulation results are in good agreement with the observations. This indicates that the nonadiabatic acceleration associated with ULF waves superposed on dipolarized magnetic field is an effective mechanism for ion energization in the near-Earth plasma sheet. The presented energy flux structures can be used as a proxy to identify the similar dynamic process.

Identification of ring current proton precipitation driven by scattering of electromagnetic ion cyclotron waves

Among the most intense emissions in the Earth's magnetosphere,electromagnetic ion cyclotron(EMIC)waves are regarded as a critical candidate contributing to the precipitation losses of ring current protons,which however lacks direct multi-point observations to establish the underlying physical connection.Based upon a robust conjunction between the satellite pair of Van Allen Probe B and NOAA-19,we perform a detailed analysis to capture simultaneous enhancements of EMIC waves and ring current proton precipitation.By assuming that the ring current proton precipitation is mainly caused by EMIC wave scattering,we establish a physical model between the wave-driven proton diffusion and the ratio of precipitated-to-trapped proton count rates,which is subsequently applied to infer the intensity of EMIC waves required to cause the observed proton precipitation.Our simulations indicate that the model results of EMIC wave intensity,obtained using either the observed or empirical Gaussian wave frequency spectrum,are consistent with the wave observations,within a factor of 1.5.Our study therefore strongly supports the dominant contribution of EMIC waves to the ring current proton precipitation,and offers a valuable means to construct the global profile of EMIC wave intensity using low-altitude NOAA POES proton measurements,which generally have a broad L-shell coverage and high time resolution in favor of near-real-time conversion of the global EMIC wave distribution.

Influence of the Phase of the Antenna Current Standing Wave on the Power Flux in Ion Cyclotron Heating

For ion cyclotron resonance heating, the current on the antenna surface exists in a form of standing wave, and the phase of the poloidal current standing wave affects significantly on the performance of the coupling. In this paper, a coupling calculation is carried out based on a practical model for the loop antenna. The ion cyclotron wave coupling performance depends greatly on the antenna current propagation constant and the phase of standing wave. For a small antenna-current-propagation constant, the antenna coupling performance is more sensitive to a π/2 change in the phase of standing wave.

Two types of mirror mode waves in the Kronian magnetosheath

A mirror mode wave is a fundamental magnetic structure in the planetary space environment that is persistently compressed by solar wind,especially in the magnetosheath.Mirror modes have been widely identified in the magnetosheaths of the Earth and other planets in the solar system,yet the understanding of mirror mode waves on extraterrestrial planets is not as comprehensive as that on the Earth.Using magnetic field data collected by the Cassini spacecraft,we found peak and dip types according to the magnetic morphology(i.e.,structures with higher or lower magnetic strengths than the background field).Moreover,mirror mode waves and electromagnetic ion cyclotron waves were found one after the other,implying that the two wave modes may evolve into one another in the Kronian magnetosheath.The results indicate that many fundamental plasma processes associated with the mirror mode structure exist in the Kronian magnetosheath.The energy conversion in Saturn’s magnetosheath may provide key insights that will aid in understanding giant planetary magnetospheric processes.

The Effects of Relative Drift Velocities Between Proton and He^(2+) on the Magnetic Spectral Signatures in the Plasma Depletion Layer

Magnetic spectrum of the electromagnetic ion cyclotron waves in the terrestrial plasma depletion layer （PDL） are sometimes observed to have a BIF （bifurcated） signature, where a diminution around 0.5Ωp with Ωp the proton gyrofrequency, occurs between two activity peaks in the spectrum. By one-dimensional hybrid simulations, the effect of relative drift velocities between protons and He2＋ on the magnetic spectral signatures in the PDL is studied. The results show that the relative drift velocity enhances the development of proton cyclotron waves and declines the development of helium cyclotron waves. The proton cyclotron waves are firstly excited, and followed by the excitation of helium cyclotron waves due to the increase in the relative drift velocity. Moreover, the boundary between two activity peaks gets obscure.

Compression-related EMIC waves drive relativistic electron precipitation

With coordinated observations of the NOAA 15 satellite and OUL magnetometer station in Finland, we report that the elec- tromagnetic ion cyclotron （EMIC） waves which were stimulated by the compression of the magnetosphere drive relativistic electron precipitation in geoquiescence on 1 Jan 2007. After an enhancement of solar wind dynamic pressure （SWDP）, a day- side Pcl pulsation was observed by the OUL station. Such a Pcl pulsation is caused by an EMIC wave which propagates from the generation source to lower altitudes. Simultaneously, the NOAA 15 satellite registered an enhancement of precipitating electron count rates with energies 〉3 MeV within the anisotropic zone of protons. This phenomenon is coincident with the quasi-linear theoretical calculation presented in this paper. Our observations suggest that after a positive impulse of solar wind, the compression-related EMIC waves can drive relativistic electrons precipitation and play a pivotal role in the dynamic of ra- diation belts.

Design of High Power DC Break For ICRH Of EAST

1.5MW Ion Cyclotron Wave Heating system was developed, the transmitter and the antenna both have their ground loops, which will severely perturb the system’s normal operation. To avoid perturbation, a DC break was designed. The S parameter and the VSWR (voltage standing wave ratio) of incident port were calculated; the thermal effect caused by conductor loss and dielectric loss was analyzed.