Quasilinear dynamics of a cloud of hot electrons propagating through a plasma in the presence of an externally applied uniform electric field

Abstract

The propagation of a cloud of hot electrons through a plasma and the generation of Langmuir waves are investigated in the presence of an externally applied uniform electric field. Using numerical simulations of the quasilinear equations the evolution of the electron distribution function and the spectral density of Langmuir waves are monitored in coordinate and velocity space. It is found that the Langmuir waves are enhanced in the presence of the electric field and the distribution functions of the beam and Langmuir waves diffuse toward large velocities. The overall self-similar characteristic of the system is preserved in the presence of the electric field. The average beam velocity is no longer constant and increases with time along its trajectory, but the acceleration is much less than that of free streaming particles. The beam number density plateaus in coordinate space and large scale, small amplitude fluctuations develop on the top of this plateau. The level of the fluctuations depends on the strength of the electric field. We also investigated the influence of the external electric field on the evolution of gas-dynamical parameters such as the height of the plateau in the beam distribution function in velocity space, its upper velocity boundary, and the local velocity spread of the beam. Due to the finite quasilinear relaxation time and spatial inhomogeneity of the electron beam, different parts of the beam are in different states of relaxation. In the region of partial relaxation the plateau is specified by both upper and lower velocity boundaries. The upper boundary of plateau increases linearly with the strength of the electric field but the lower boundary is independent of it. Contrary to the free streaming of a beam in an electric field or quasilinear relaxation in the absence of the electric field, the local velocity spread of the beam increases during its propagation. Some of the electrons at the back of the beam are also transferred by the electric field to its front, so that the height of plateau increases at large distances.

Plasma Emission by Nonlinear Electromagnetic Processes

“…Now that we have examined the three sample cases, we next investigate the details of the various physical processes in each case in further detail. The physics of electron-beam, Langmuir, and ion-sound turbulence processes, and in some cases, also the radiation generation processes based upon reduced methods, have been investigated in detail by the present authors in our previous publications as well as by others (Ziebell et al 2001, 2014a, 2014b, 2014c, Kontar & Pécseli 2002Li et al 2003Li et al , 2005aLi et al , 2005bLi et al , 2006aLi et al , 2006bLi et al , 2006cLi et al , 2008aLi et al , 2008bLi et al , 2009Li et al , 2010Li et al , 2011aLi et al , 2011bLi et al , 2011cForoutan et al 2007;Ratcliffe et al 2012;Schmidt & Cairns 2012a. The novel aspect of the present investigation is the addition of EM effects without recourse to any preliminary assumptions such as one radiation emission mechanism being dominant over others, etc.…”

Evolution of gas-dynamical parameters of an electron beam in an inhomogeneous plasma with an external electric field

“…To study the effects of the plasma density gradient and the presence of a uniform external electric field on the gas-dynamical parameters of a beam, we plot contours of the upper boundary of the plateau u 2 in figures 1(a1)-(a4) and the lower boundary velocity u 1 in figures 1(b1)-(b4) for four different background densities and electric fields. In a homogeneous plasma and in the absence of an electric field, the upper boundary of the plateau shows self-similar evolution, with u 2 = 2x/t, so we see that the contours of constant u 2 are straight lines [9]. It is seen that in the presence of density gradient, the contours of constant u 2 deviate from straight lines.…”

“…In space plasma, large-scale dc electric fields are mostly generated in magnetic loops and magnetic reconnection regions having a component parallel to the magnetic field; hence these fields have an important role in the acceleration of particles to large velocities [8,9]. Moreover, the density of the solar wind plasma decreases with distance from the corona to the Earth [10,11].…”

Simulation study of collisional effects on the propagation of a hot electron beam and generation of Langmuir turbulence for application in type III radio bursts

“…This approach is called quasi-gas-dynamical or shortly gas-dynamical description of the quasi-linear system. In the gas-dynamic description, it is assumed that the beam distribution is always in a plateaued state and characterized by its height and upper boundary in velocity space (Foroutan et al 2005(Foroutan et al , 2007a(Foroutan et al ,b, 2008Khalilpour et al 2009;Khalilpour and Foroutan 2011).…”