Ion acoustic damping effects on parametric decays of Alfvén waves: Right‐hand polarization

Abstract

Abstract. We study ion acoustic damping effects on parametric decays of right-handpolarized electromagnetic waves. We do this because ion beams have been observed in a variety of space environments, and consequently, these waves can exist in those places. Damping effects are incorporated into the model by adding to the longitudinal component of the equation of motion a collision-like term. Like for left-hand-polarized waves, the effect of damping is twofold. On the one hand, damping decreases the maximum growth rate of the existing instabilities while increasing the instability range, and on the other hand, it destabilizes regions that are stable in the absence of damping. Thus, for lowfrequency pump waves, to 0 << tOci , and for low/3 = vt/v• (tOci is the ion gyrofrequency, and vt and v• are the thermal and the Alfv•n velocities, respectively), where the only parametric instability is a decay instability, damping destabilizes the frequency range between to = 0 and the threshold of the decay instability. As/3 increases, two new parametric instabilities develop: One of them is a modulational instability, and above some threshold value of the pump wave amplitude, there is also a beat wave instability. The decay instability is also possible for pump wave amplitude above some threshold. For even larger/3 the decay instability is no longer possible. In all cases, damping effects reduce the growth rate of the existing instabilities and destabilize regions which are stable in the absence of damping. These results are in agreement with those obtained by Vasquez [1995]. It is also shown that for large-frequency pump waves, electron/ion whistler waves, the decay instability reappears even for large/3 and has very large growth rates.

Linear and nonlinear electromagnetic and electrostatic instabilities in a plasma with two ion beams

“…However, a fluid model is sufficient to provide a general survey of possible wave couplings, saturation effects, and nonlinear purely electrostatic instabilities. Although it would be desirable to solve the problem using kinetic theory, hybrid simulations seem to confirm the results obtained by using a collision like term in the fluid equations in order to simulate Landau damping [ Inhester , 1990; see Hollweg et al , 1993; Vasquez , 1995; Gomberoff , 2000; Gomberoff and Araneda , 2001; Gomberoff , 2000; Gomberoff et al , 2001, 2005; Araneda et al , 2007].…”

Behavior of linear beam-plasma instabilities in the presence of finite amplitude circularly polarized waves

“…(5), are invariant under a rotation through an angle of 180 o . Therefore, it is sufficient to analyze the solutions in the upper half ω − k plane [9,10,20,14,15,16]. Note that for A = 0, only the ion-acoustic modes depend on the temperature.…”

“…The effect and the evolution of the beam for right and left handed polarized waves, have also been studied by using simulation experiments [17]. These studies have considered linearly stable systems [9,10,14,15,16]. Proton beams observed in the solar wind display large drift velocities which can be larger than the necessary velocity to generate a linear beam-plasma instability [18].…”

“…Their nonlinear evolution has also been studied by using drift kinetic effects [12] and hybrid computer simulation techniques [13]. Studies have been carried out by [14,15,16], including the effects of dissipation and of the beam drift speed. The effect and the evolution of the beam for right and left handed polarized waves, have also been studied by using simulation experiments [17].…”

Ion Dynamics During the Parametric Instabilities of a Left-Hand Polarized Alfvén Wave in a Proton-Electron-Alpha Plasma

“…However, when the compression effect is taken into account, the Alfvén waves will become unstable to the parametric instabilities (Galeev & Oraevskii 1963;Goldstein 1978;Wong & Goldstein 1986;Jayanti & Hollweg 1993a, 1993bHollweg 1994;Gomberoff et al 2001;Del Zanna et al 2001;, which has been a hot topic in the plasma community since the 1960s. Galeev & Oraevskii (1963) first studied the evolution of a monochromatic Alfvén wave and showed that it is unstable to the parametric decay in a low beta plasma.…”