Preferential perpendicular acceleration of heavy ionospheric ions by interactions with electrostatic hydrogen cyclotron waves

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[1] When multi-ion plasma consisting of heavy and light ions is permeated by a lowfrequency Alfvén (LFA) wave, the crossed-electric-and-magnetic field (E Â B), and the polarization drifts of the different ion species and the electrons could be quite different. The relative drifts between the charged-particle species drive waves, which energize the plasma. Using 2.5-dimensional (2.5-D) particle-in-cell simulations, we study this process of wave generation and its nonlinear consequences in terms of acceleration and heating plasma. Specifically, we study the situation for LFA wave frequency being lower than the heavy-ion cyclotron frequency in a multi-ion plasma. We impose such a wave to the plasma assuming that its wavelength is much larger than that of the waves generated by the relative drifts. For better understanding, the LFA-wave driven simulations are augmented by those driven by initialized ion beams. The driven high-frequency (HF) wave modes critically depend on the heavy ion density n h ; for small values of n h , the lower hybrid (LH) waves dominate. On the other hand, for large n h a significantly enhanced level of waves occurs over a much broader frequency spectrum below the LH frequency and such waves are interpreted here as the ion Bernstein (IB) mode near the light ion cyclotron harmonics. Irrespective of the driven wave modes, both the light and heavy ions undergo significant transverse acceleration, but for the large heavy-ion densities, even the electrons are significantly accelerated in the parallel direction by the waves below the LH frequency. Even when the LFA wave drive is maintained, the ion heating leads to the cessation of HF wave excitation just after a few cycles of the former wave. On the basis of marginal stability seen in the simulations, an empirical relation for LFA wave amplitude, frequency and ion temperature is given. INDEX TERMS: 2159Interplanetary Physics: Plasma waves and turbulence; 2483 Ionosphere: Wave/particle interactions; 2772 Magnetospheric Physics: Plasma waves and instabilities; 7843 Space Plasma Physics: Numerical simulation studies; 7871 Space Plasma Physics: Waves and instabilities; KEYWORDS: Alfvén waves, ion heating, waveparticle interactions, lower hybrid waves Citation: Singh, N., and G. Khazanov (2004), Numerical simulation of waves driven by plasma currents generated by low-frequency Alfvén waves in a multi-ion plasma,

Section: Numerical Resultsmentioning

confidence: 99%

Numerical simulation of waves driven by plasma currents generated by low‐frequency Alfvén waves in a multi‐ion plasma

Singh

2004

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“…This behavior of the heating by a broadband turbulence is in contrast to the heating by a coherent ion cyclotron wave [Singh et al, 1981[Singh et al, , 1982. In the latter case, heavier ions are preferentially heated [Papadopoulos et al, 1980;Singh et al, 1983].…”

Section: Discussionmentioning

confidence: 89%

“…There are already many papers on the subject [cf. Singh et al, 1983, and references therein]. Observations from the S3-3 satellite have shown that in and above the auroral acceleration region the wave turbulence is dominated by coherent ion cyclotron waves, which correlate with ion beams [Kintner et al, 1979].…”

Section: Introductionmentioning

confidence: 99%

“…Observations from the S3-3 satellite have shown that in and above the auroral acceleration region the wave turbulence is dominated by coherent ion cyclotron waves, which correlate with ion beams [Kintner et al, 1979]. The heating of ions by such waves has been recently studied by Lysak et al [1980], Papadopoulos et al [1980], and Singh et al [1981Singh et al [ , 1982Singh et al [ , 1983]. On the other hand, waves below the acceleration region are generally found to be very broadband [Ternerin et at., 1981].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Energization of ions in the auroral plasma by broadband waves: Generation of ion conics

Singh¹,

Schunk²

1984

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The ion conics provide an important mechanism for the transportation of ionospheric ions to the magnetosphere. The conics are generated by a transverse acceleration of the ions and by the subsequent upward repulsion by the magnetic mirror force. Here, the acceleration of ions by a broadband lower hybrid (LH) wave is considered. Since the broadband waves have a finite correlation time, the heating occurs even in the absence of a resonance between the ions and the waves. The LH waves excited by precipitating energetic electrons in the auroral ionosphere have characteristics such that ambient cold ions (<1 eV) cannot resonate with the waves. Thus the nonresonant heating mechanism discussed here may play a direct role in generating ion conics with energies of about a few hundred electron volts at altitudes below the auroral acceleration region where the lower hybrid waves have been observed. The nonresonant mechanism may also act to preheat the ions so that the resonant heating can follow. The extent of the energy gain of H+ ranges from a few electron volts to a few keV as the turbulence noise level varies from 10−9 to 10−6 V² m−2 s−1. The heavy ion gains comparably less energy. The calculations were done for turbulence regions that were both extended and limited in distance, the latter being particularly relevant to the generation of conics with very sharp pitch angle distributions.

“…Furthermore, Lysak and Carlson [ 1981 ] show that with the inclusion of microscopic turbulence the Allyen wave may not bounce back and forth and a steady state can be established in one bounce. Singh et al [1981Singh et al [ , 1982Singh et al [ , 1983…”

Section: Equal O + and H + Streaming Speeds Reported By Frank Et Al mentioning

confidence: 99%

A possible mechanism for the observed streaming of O⁺ and H⁺ ions at nearly equal speeds in the distant magnetotail

Singh¹,

Schunk²

1985

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Several observations have been reported of O+ and H+ ions streaming away from the earth with nearly equal velocities in the distant magnetotail region. In these events, the O+ ions have an energy in the range 320–3200 eV, while the H+ ions are less energetic by a factor which is approximately equal to the O+/H+ mass ratio. A possible explanation for the creation of such streaming events is presented. The mechanism involves the acceleration of O+ and H+ ions through their interaction with electrostatic hydrogen cyclotron (EHC) waves on auroral field lines at altitudes above parallel potential drops. The H+ and O+ ions are accelerated sequentially in the following manner. When an upward flowing H+ ion beam interacts with a cold background H+ ion plasma, EHC waves can be strongly excited. These waves heat the cold background H+ ions to an average energy (W(H+)) in the range of from a few tens to a few hundreds of electron volts. The resulting pitch angle distribution of the energized H+ ions peaks at angles near 110°, which leads to an upward flowing ion cloud in the northern hemisphere. When a fresh H+ ion beam permeates this warm H+ ion cloud, weak EHC waves can be excited if the beam energy is near that needed for marginal instability. If the H+ ion beam is accompanied by an O+ ion beam, part of the O+ beam can interact with the weak EHC waves, producing O+ ions with energies W(O+) ≃ 16 W(H+), and the pitch angle distribution of these O+ ions matches that of the warm H+ ions. When such a synchronism is achieved, the O+ and H+ ions stream together along the field lines away from the source region. In the distant magnetotail, their pitch angle distribution becomes field‐aligned owing to the magnetic mirror force.