Study of EMIC wave excitation using direct ion measurements (original) (raw)
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A laboratory study of collisional electrostatic ion cyclotron waves
Journal of Geophysical Research, 1986
The effects of neutral-particle collisions on current-driven electrostatic ion cyclotron (EIC) waves are studied in a Q machine with a cesium (Cs +) plasma. We find that even when vin --0.312ci, EIC waves of substantial amplitude (/Xn/n of several percent) can be excited.
Journal of Geophysical Research: Space Physics, 2013
1] A cold electron heating event associated with electromagnetic ion cyclotron (EMIC) waves is observed and modeled. The observational data of particles and waves are collected by the Thermal Emission Imaging System spacecraft at magnetic local time 17.0-17.2. During this event, intense He + band EMIC waves with the peak frequency 0.25 Hz are excited, corresponding to the observed phase space density (PSD) of distinct anisotropic ions. Meanwhile, substantial enhancements in energy flux of cold (1-10 eV) electrons are observed in the same period. The energy flux of electrons below 10 eV is increased by several to tens of times. We use a sum of kappa distribution components to fit the observed ion PSD and then calculate the wave growth rate driven by the anisotropic hot protons. The calculated result is in good agreement with the in situ observation. Then, we investigate whether the excited EMIC waves can transfer energy to cold electrons by Landau resonant absorption and yield electron heating. Using the typical Maxwellian distribution for cold electrons, we evaluate the wave damping rates resulted from the cold electrons in gyroresonance with EMIC waves. The simulating results show that the strong wave growth region in the He + band induced by anisotropic ions corresponds to the strong wave damping region driven by cold electrons. Moreover, cold electrons can be heated efficiently at large wave normal angles. The current results provide a direct observational evidence for EMIC-driven cold electron heating-a potential mechanism responsible for stable auroral red arc.
Convection of ion cyclotron waves to ion-heating regions
Journal of Geophysical Research, 1991
Low-frequency waves associated with ion conics have been observed in the ;:entral plasma sheet, in a region where there are no obvious sources of free energy that could destabiliz•,these waves locally. We consider ion cyclotron waves generated in the equatorial plane b•. a i•rotot•' temperature anisotropy and use computed growth rates to create a model wave distri.bution. U•ing raj•t•'?• ing and conservation of the wave distribution function along phase space rays, w.e. th, eri map the; Wave intensities from the equatorial plane to the top of the ion-heating region. We find that •he spectral density at a geocentric distance of 2.8 RE will be about 10 times higher than that in the equatorial region. Thus, convection from the equatorial plane could explain the observed spectral density of 10-(; V 2 m-2 Hz-1 and the associated oxygen ion heating. iNTRODUCTION It is well known that ions in the ionosphere and magnetosphere can be heated perpendicularly to the geomagnetic field. These ions may then move adiabatically up the field lines of the inhomogeneous terrestrial magnetic field and form so-called conics in velocity space. Several alternative ion energization mechanisms have been suggested (see reviews by Klumpar [1986], Lysak [1986], and Chang et al., [1988], and references therein). However, the problem of ion conic generation is still the subject of vigorous debate. At least at altitudes above a few thousand kilometers, ion conics are often observed on the same field lines as relatively intense, broadband waves. Several studies indicate that the waves observed around the ion gyrofrequency may, via resonant cyclotron heating, generate the observed ion conics [Chang et al., 1986; Andrd et al., 1988, 1990; Crew et al., 1990]. Waves at roughly half the ion gyrofrequency may via double-cyclotron absorption contribute to the ion heating ITemerin and Roth, 1986; Ball, 1989; Ball and Andrd, 1991a]. Emissions at even lower frequencies may also cause some ion energization [Lundin and Hultqvist, 1989; Lundin et al., 1990; Ball and Andrd, 1991b]. Broadband waves and ion conics are often observed above the auroral zone and in the polar cusp/cleft region. Here local energy sources such as sharp gradients and drifting particles can possibly generate some of the waves. However, broadband waves associated with ion conics are also common in the central plasma sheet [Chang et ai., 1986]. In this region, equatorward of the auroral zone, there are no obvious local energy sources that can power the broadba• waves. This led Johnson et [1989] to suggest that the waves are generated by anisotropic ion distributions in the equatorial plane and that they then propagate down the field lines. Closely related ideas were considered recently •lso by Horne and Thorne [1990], who used ray tracing to study the propagation of ion cyclotron waves in the plasmapause region. They emphasized ion cyclotron damping at the second harmonic of the oxygen gyrofrequency. The path-integrated absorption they computed was used to estimate the ion heating qualitatively, but their method did not allow quantitative comparisons based on observed spectral densities.
Stability of electrostatic ion cyclotron waves in a multi-ion plasma
Pramana-journal of Physics, 2009
We have studied the stability of the electrostatic ion cyclotron wave in a plasma consisting of isotropic hydrogen ions (H+) and temperature-anisotropic positively (O+) and negatively (O−) charged oxygen ions, with the electrons drifting parallel to the magnetic field. Analytical expressions have been derived for the frequency and growth/damping rate of ion cyclotron waves around the first harmonic of both hydrogen and oxygen ion gyrofrequencies. We find that the frequencies and growth/damping rates are dependent on the densities and temperatures of all species of ions. A detailed numerical study, for parameters relevant to comet Halley, shows that the growth rate is dependent on the magnitude of the frequency. The ion cyclotron waves are driven by the electron drift parallel to the magnetic field; the temperature anisotropy of the oxygen ions only slightly enhance the growth rates for small values of temperature anisotropies. A simple explanation, in terms of wave exponentiation times, is offered for the absence of electrostatic ion cyclotron waves in the multi-ion plasma of comet Halley.
Stability of electrostatic ion cyclotron waves in a multi-ion plasmay
We have studied the stability of the electrostatic ion cyclotron wave in a plasma consisting of isotropic hydrogen ions (H + ) and temperature-anisotropic positively (O + ) and negatively (O − ) charged oxygen ions, with the electrons drifting parallel to the magnetic field. Analytical expressions have been derived for the frequency and growth/damping rate of ion cyclotron waves around the first harmonic of both hydrogen and oxygen ion gyrofrequencies. We find that the frequencies and growth/damping rates are dependent on the densities and temperatures of all species of ions. A detailed numerical study, for parameters relevant to comet Halley, shows that the growth rate is dependent on the magnitude of the frequency. The ion cyclotron waves are driven by the electron drift parallel to the magnetic field; the temperature anisotropy of the oxygen ions only slightly enhance the growth rates for small values of temperature anisotropies. A simple explanation, in terms of wave exponentiation times, is offered for the absence of electrostatic ion cyclotron waves in the multi-ion plasma of comet Halley.
Journal of Geophysical Research: Space Physics, 2013
1] Understanding excitation of electromagnetic ion cyclotron (EMIC) waves remains a considerable scientific challenge in the magnetospheric physics. Here we adopt correlated data from the Thermal Emission Imaging System (THEMIS) spacecraft under low (K p = 1 + ) and medium (K p = 4) geomagnetic activities to investigate the favorable conditions for the excitation of EMIC waves. We utilize a sum of bi-Maxwellian components and kappa components to fit the observed ion (6-25 keV) distributions collected by the electrostatic analyzer (ESA) onboard the THEMIS spacecraft. We show that the kappa distribution models better and more smoothly with the observations. Then we evaluate the local growth rate and path-integrated gain of EMIC waves by bi-Maxwellian and kappa distributions, respectively. We demonstrate that the path-integrated wave gain simulated from the kappa distribution is consistent with observations, with intensities 24 dB in H + band and 33 dB in He + band. However, bi-Maxwellian distribution tends to overestimate the wave growth rate and path-integrated gain, with intensities 49 dB in H + band and 48 dB in He + band. Moreover, compared to the He + band, a higher proton anisotropy is needed to excite the H + band waves. The current study presents a further observational support for the understanding of EMIC wave instability under different geomagnetic conditions and suggests that the kappa-type distributions representative of the power law spectra are probably ubiquitous in space plasmas.
Effect of heavy ions on ponderomotive forces due to ion cyclotron waves
Journal of Geophysical Research, 1998
We study ponderomotive effects induced by the electromagnetic ion cyclotron (EMIC) waves in the Pcl frequency band (0.2 to Hz) in a two-ion (H + and one heavy ion, e.g., He +) plasma. Near the dayside boundary of the magnetosphere, the ponderomotive forces lead to a noticeable accumulation of cold plasma along the field line in two regions of minimum magnetic field intensity located symmetrically around the equator. In the inner magnetosphere, one maximum of cold plasma at the equator is found. At frequencies less than the heavy ion gyrofrequency, the accumulation of cold plasma increases with increasing heavy ion concentration. At frequencies above the heavy ion gyrofrequency, the ponderomotive forces due to EMIC waves are enhanced because of a resonance at the stop band frequencies. We investigate the stop band structure of EMIC waves in a nondipolar magnetosphere and discuss the properties of wave propagation along the field line for different heavy ion plasma concentrations. 1. Introduction Considerable attention has been paid to study the influence of heavy ions (mainly oxygen and helium) on the dynamics of electromagnetic ion cyclotron waves in the Pc1 frequency range (0.2 to 5.0 Hz). Using the searchcoil magnetometer and particle spectrometer data onboard GEOS i and ATS 6 satellites, Young et al. [1981] and Mauk et al. [1981] came to the conclusion that EMIC waves are strongly controlled by the dynamics of heavy ions. Later on, Fraser et al. [1986] obtained similar results using ISEE i and 2 data. The propagation of EMIC waves along magnetic field lines in a heavy ion rich plasma is characterized by the reversal of polarization and the splitting of spectrum into two branches, the high-frequency branch w (f•i stands for the heavy ion gyrofrequency) and the low-frequency branch w < f•i. The two branches are separated by a stop band whose width is roughly f•i(Ni/N) [(mi/mp)-1]. Here mp and mi stand for proton and heavy ion masses, respectively, and N is the total plasma density (N = N, = Nv + N•). Observations
Journal of Geophysical Research, 1991
Quasi-monochromatic waves at -1.2 f r.H, where f r.H is the hydrogen cyclotron frequency, were observed as the ISEE 1 satellite traversed auroral field lines at radial distances of -2.5-4.5 R•r near midnight on June 19, 1981. The waves were polarized perpendicular to the magnetic field (k#/k I _<0.2). In addition, there were waves at slightly above both the helium and the oxygen cyclotron frequencies. The waves occurred within a region of reduced density (-0.1-0.2/cm 3) with the electron temperature greater than the ion temperature, upflowing hydrogen and oxygen beams, and weak field-aligned currents bounded by electrostatic shocks. The wave characteristics and associations were similar to those observed at lower altitudes by the S3-3 satel-
Velocity-shear-driven ion-cyclotron waves and associated transverse ion heating
Journal of Geophysical Research: Space Physics, 1998
Recent sounding rocket experiments, such as SCIFER, AMICIST, and ARCS-4, and satellite data from FAST, Freja, DE-2, and HILAT, provide compelling evidence of a correlation between small-scale spatial plasma inhomogeneities, broadband low-frequency waves, and transversely heated ions. These naturally arising, localized inhomogeneities can lead to sheared cross-magnetic-field plasma flows, a situation that has been shown to have potential for instability growth. Experiments performed in the Naval Research Laboratory's Space Physics Simulation Chamber demonstrate that broadband waves in the ion-cyclotron frequency range can be driven solely by a transverse, localized electric field, without the dissipation of a field-Migned current. Significant perpendicular ion energization resulting from these waves has been measured. Detailed comparisons with both theoretical predictions and space observations of electrostatic waves found in the presence of sheared cross-magnetic-field plasma flow are made. FAC is accompanied by sheared cross-field particle flows 1permanently at Sachs-Freeman Associates, Inc., Largo, Maryland.
Stability of Electrostatic Ion Cyclotron Harmonic Waves in a Multi-ion Plasma
V and dH V + , respectively, along the ambient magnetic field and positively and negatively charged oxygen ions constitute the plasma under consideration. This composition very well approximates the plasma environment around a comet. Analytical expressions for the frequency and growth / damping rate of the EIC waves around the higher harmonics of hydrogen ion gyrofrequency have been derived. The EIC waves propagate at frequencies around the harmonics of the hydrogen ion gyrofrequency and the wave growth decreases rapidly for higher harmonics. We find that, the wave can be driven unstable by the hydrogen ion drift velocity dH V + alone, at small k⊥ρLH+ as well as electron drift velocity de V at large LH k ρ ⊥ + . Also, the growth rate is dependent on the densities and temperature anisotropies of the various constituent ions.