Role of Parallel Solenoidal Electric Field on Energy Conversion in 2.5D Decaying Turbulence with a Guide Magnetic Field

We perform 2.5D particle-in-cell simulations of decaying turbulence in the presence of a guide (out-of-plane) background magnetic field. The fluctuating magnetic field initially consists of Fourier modes at low wavenumbers (long wavelengths). With time, the electromagnetic energy is converted to plasma kinetic energy (bulk flow+thermal energy) at the rate per unit volume of J · E for current density J and electric field E . Such decaying turbulence is well known to evolve toward a state with strongly intermittent plasma current. Here we decompose the electric field into components that are irrotational, E ir, and solenoidal (divergence-free), E so. E ir is associated with charge separation, and J · E ir is a rate of energy transfer between ions and electrons with little net change in plasma kinetic energy. Therefore, the net rate of conversion of electromagnetic energy to plasma kinetic energy is strongly dominated by J · E so, and for a strong guide magnetic field, this mainly involves the component E so,∥ parallel to the total magnetic field B . We examine various indicators of the spatial distribution of the energy transfer rate J ∥ · E so,∥, which relates to magnetic reconnection, the best of which are (1) the ratio of the out-of-plane electric field to the in-plane magnetic field, (2) the out-of-plane component of the nonideal electric field, and (3) the magnitude of the estimate of current helicity

Electron acceleration by a circularly polarized electromagnetic wave publishing in plasma with a periodic magnetic field and an axial guide magnetic field

In this paper, we study the electron acceleration by a circularly polarized electromagnetic wave propagating through plasma in the presence of a periodic and an axial guide magnetic field. A numerical calculation in MATLAB software was developed by employing the fourth-order Runge–Kutta method for studying the electron energy and electron trajectory in plasma medium. The equations governing the electron momentum and energy which describe electron acceleration by a circularly polarized laser pulse have been obtained. It is shown that by choosing an appropriate wiggler field frequency at short distances, the electron retains an adequate amount of energy. In addition, it is found that due to the simultaneous existence of the wiggler field and field of laser pulse and their combined effects, the electron in the direction of the laser pulse propagating, turns around and subsequently, the electron transverse momentum increases and as a result the electron escapes from the laser pulse near the laser pulse peak. Furthermore, it is seen that by increasing the laser intensity, the electron energy decreases and by decreasing to an appropriate value while employing a wiggler magnetic field, a higher peak of energy is gained.

Dispersion relation and growth rate of a relativistic electron beam propagating through a Langmuir wave wiggler

In this study, a theory of free-electron laser (FEL) with a Langmuir wave wiggler in the presence of an axial magnetic field has been presented. The small wavelength of the plasma wave (in the sub-mm range) allows obtaining higher frequency than conventional wiggler FELs. Electron trajectories have been obtained by solving the equations of motion for a single electron. In addition, a fourth-order Runge–Kutta method has been used to simulate the electron trajectories. Employing a perturbation analysis, the dispersion relation for an electromagnetic and space-charge waves has been derived by solving the momentum transfer, continuity, and wave equations. Numerical calculations show that the growth rate increases with increasing the e-beam energy and e-beam density, while it decreases with increasing the strength of the axial guide magnetic field.