Evolution of electron beam generated waves resulting in transverse ion heating and filamentation of the plasma

2003

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Abstract. We report here further results from the threedimensional particle-in-cell simulations of the electron-beam driven electron holes. We focus here on (i) the transformation of oscillatory waves driven by the electron-beam instability into electron holes, (ii) the continued evolution and propagation of electron holes after their formation, including merging of electron holes, and (iii) the effects of the evolution on the plasma density and ion velocity distribution function. We find that initially electron-beam modes with perpendicular wave numbers k ⊥ = 0 and as well as k ⊥ = 0 are driven resonantly below the electron plasma frequency of the target plasma. The modes interact nonlinearly and modulate each other both in space and time, producing wave structures with finite perpendicular scale lengths. Nonlinear evolution of such wave structures generates the electron holes in the simulations. Initially, a large number of electron holes form in the plasma. Their merging yields continuously a decreasing number of electron holes. The propagation velocity of the electron holes evolves dynamically and is affected by their merging. At late times only a few electron holes are left in the simulation and they decay by emitting low-frequency electrostatic whistler waves just above the lower hybrid (LH) frequency ω h . These waves, which are long structures parallel to the ambient magnetic field B 0 and quite short transverse to B 0 , are associated with similar structures in the plasma density, producing density filaments. It turns out that electronbeam driven plasmas, in general, develop such filaments at some stage of the evolution of the beam-driven waves. In view of the excitation of the LH waves near ω h , which could resonate with the ions, an analysis shows that it is possible to heat transversely the ions in a time scale of a few seconds in the auroral return current plasma, in which electron holes and transversely heated ions have been simultaneously observed.

Section: Propagation Velocitycontrasting

confidence: 41%

Section: Propagation Velocitymentioning

confidence: 94%

Section: Simulation Modelmentioning

confidence: 99%

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Space-time evolution of electron-beam driven electron holes and their effects on the plasma

2003

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“…Useful information about the life-time of the electronholes and ion heating is provided by the 2-D and 3-D particle simulations of the electron-beam driven instabilities (Omura et al, 1999;Goldman et al, 2000;Singh et al, 2001b). 3-D simulations of the electron-beam driven electron holes reveal that initially a large number of electron holes are formed.…”

Section: Discussionmentioning

confidence: 99%

Electron acoustic solitary waves with non-thermal distribution of electrons

Lakhina

2004

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122

Abstract. Electron-acoustic solitary waves are studied in an unmagnetized plasma consisting of non-thermally distributed electrons, fluid cold electrons and ions. The Sagdeev pseudo-potential technique is used to carry out the analysis. The presence of non-thermal electrons modifies the parametric region where electron acoustic solitons can exist. For parameters representative of auroral zone field lines, the electron acoustic solitons do not exist when either α > 0.225 or T c /T h > 0.142, where α is the fractional non-thermal electron density, and T c (T h ) represents the temperature of cold (hot) electrons. Further, for these parameters, the simple model predicts negatively charged potential structures. Inclusion of an electron beam in the model may provide the positive potential solitary structures.

“…It is seen that the initial evolution to bipolar structures in the xdirection, the direction of the ambient magnetic field, is followed by the excitation of whistlers, which dominate at later times. Singh et al (2001b) have performed 3-D particle simulation of electron beam driven instabilities to explain the characteristics of the solitary structures observed on the auroral field lines. Figure 7 shows some results of their simulations for a finite-sized fast electron beam with V b /V te = 8.…”

Section: Bgk Modes/phase Space Holesmentioning

confidence: 99%

Some theoretical models for solitary structures of boundary layer waves

Lakhina

Tsurutani

et al. 2003

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Abstract. Solitary electrostatic structures have been observed in and around auroral zone field lines at various altitudes ranging from close to the ionosphere, to the magnetopause low-latitude boundary layer (LLBL) and cusp on the dayside, and to the plasma sheet boundary layer on the nightside. In this review, various models based on solitons/double layers and BGK modes or phase space holes are discussed in order to explain the characteristics of these solitary structures.