Ion acoustic double layers and solitons in auroral plasma

106

Abstract. Large amplitude ion-acoustic and electronacoustic waves in an unmagnetized multi-component plasma system consisting of cold background electrons and ions, a hot electron beam and a hot ion beam are studied using Sagdeev pseudo-potential technique. Three types of solitary waves, namely, slow ion-acoustic, ion-acoustic and electron-acoustic solitons are found provided the Mach numbers exceed the critical values. The slow ion-acoustic solitons have the smallest critical Mach numbers, whereas the electron-acoustic solitons have the largest critical Mach numbers. For the plasma parameters considered here, both type of ion-acoustic solitons have positive potential whereas the electron-acoustic solitons can have either positive or negative potential depending on the fractional number density of the cold electrons relative to that of the ions (or total electrons) number density. For a fixed Mach number, increases in the beam speeds of either hot electrons or hot ions can lead to reduction in the amplitudes of the ion-and electron-acoustic solitons. However, the presence of hot electron and hot ion beams have no effect on the amplitudes of slow ion-acoustic modes. Possible application of this model to the electrostatic solitary waves (ESWs) observed in the plasma sheet boundary layer is discussed.

Section: Introductionmentioning

confidence: 99%

Study of nonlinear ion- and electron-acoustic waves in multi-component space plasmas

Lakhina

Singh

Kakad

et al. 2008

106

“…It was considered that an ion acoustic mode necessarily show a decrease in the width with increasing amplitude while an opposite trend indicates the presence of BGK modes in the space. However, unlike electron solitary holes (Muschietti et al, 1999b;Maslov and Schamel, 1993), the observed rarefactive structures in the auroral region (Temerin et al, 1982;Böstrom et al, 1989) were mainly interpreted as the evolution of ion acoustic mode (Reddy and Lakhina, 1991). Berthomier et al (1998) have shown that a fully nonlinear rarefactive ion acoustic wave in an unmagnetized plasma may show an increase in the width with increasing amplitude.…”

Section: Anomalous Widthmentioning

confidence: 99%

“…The problem of the formation of weak double layers was also addressed on the basis of the theory of ion acoustic waves (Gray et al, 1991) and was suggested as the result of the evolution of ion acoustic solitary waves (Berthomier et al, 1998). The possible existence of solitary waves in the ion acoustic frequency range triggered several theoretical and numerical investigations (Qian et al, 1988;Koskinen et al, 1990;Gray et al, 1991;Yadav and Sharma, 1990;Reddy and Lakhina, 1991;Reddy et al, 1992;Cairns et al, 1995;Sato and Okuda, 1980). In most of the cases they were described as rarefactive ion acoustic solitary waves and their analysis were based on a weakly nonlinear theory such as the K-dV equation (Washimi and Taniuti, 1966;Nishihara and Tajiri , 1981;Buti, 1980a).…”

Section: Introductionmentioning

confidence: 99%

Anomalous width variation of rarefactive ion acoustic solitary waves in the context of auroral plasmas

Ghosh

Lakhina

2004

Abstract. The presence of dynamic, large amplitude solitary waves in the auroral regions of space is well known. Since their velocities are of the order of the ion acoustic speed, they may well be considered as being generated from the nonlinear evolution of ion acoustic waves. However, they do not show the expected width-amplitude correlation for K-dV solitons. Recent POLAR observations have actually revealed that the low altitude rarefactive ion acoustic solitary waves are associated with an increase in the width with increasing amplitude. This indicates that a weakly nonlinear theory is not appropriate to describe the solitary structures in the auroral regions. In the present work, a fully nonlinear analysis based on Sagdeev pseudopotential technique has been adopted for both parallel and oblique propagation of rarefactive solitary waves in a two electron temperature multiion plasma. The large amplitude solutions have consistently shown an increase in the width with increasing amplitude. The width-amplitude variation profile of obliquely propagating rarefactive solitary waves in a magnetized plasma have been compared with the recent POLAR observations. The width-amplitude variation pattern is found to fit well with the analytical results. It indicates that a fully nonlinear theory of ion acoustic solitary waves may well explain the observed anomalous width variations of large amplitude structures in the auroral region.

“…(1)-(7) for soliton solutions, we shall use the reductive perturbation method (Washimi and Taniuti, 1966;Reddy and Lakhina, 1991). We introduce the stretched variables…”

Section: Rarefactive Solitonsmentioning

confidence: 99%

Electron acoustic solitons in the Earth's magnetotail

Tagare

Singh

Reddy

et al. 2004

Abstract. Small amplitude electron -acoustic solitons are studied in a magnetized plasma consisting of two types of electrons, namely cold electron beam and background plasma electrons and two temperature ion plasma. The analysis predicts rarefactive solitons. The model may provide a possible explanation for the perpendicular polarization of the low-frequency component of the broadband electrostatic noise observed in the Earth's magnetotail.