The nonlinear dynamics of low frequency Buneman instability in a current-driven cold unmagnetized... more The nonlinear dynamics of low frequency Buneman instability in a current-driven cold unmagnetized plasma are studied using particle in cell simulation. Simulations of the Buneman instability show that the electron density profile has sharp peaks and the amplitude of the peaks changes with time. Also, the nonlinear evolution of this instability and saturation time is investigated by the time variation of the electric potential energy in the plasma. Moreover, the electron trapping phenomena and the formation of phase space electron holes are presented by considering the phase space diagram and electron distribution function. Finally, the ion mass effect on saturation time is investigated and it is found that the saturation time increases by increasing the ion mass and the saturation level is not very sensitive to the ion mass.
The nonlinear dynamics of filamentation instability in a weakly ionized current-carrying plasma i... more The nonlinear dynamics of filamentation instability in a weakly ionized current-carrying plasma in the diffusion frequency region is studied using particle in cell simulation. The effects of electron thermal motion and ion-neutral collision on the evolution of this instability in the nonlinear stage of the filaments coalescence are discussed. It is found that the coalescence of the current filaments is enhanced by increasing the temperature and is delayed by increasing the collision frequency.
The attosecond pulse generation by the interaction of two counterpropagating ultrashort laser pul... more The attosecond pulse generation by the interaction of two counterpropagating ultrashort laser pulses with near-critical density plasma is simulated using two-dimensional particle in the cell method. Results of the simulations showed the flying mirror properties such as density and shape change, while moving through the plasma, behind the intense driver laser. We investigated the effects of the mirror features on the produced attosecond pulse intensity by setting various delay times between the driver and source pulses so that the source encounters the mirror at different points. It is demonstrated that the higher density of the mirror, particularly in its center (due to the Gaussian transverse profile of the source), in addition to its suitable curvature and surface smoothness, results in a more intense reflection. Moreover, a considerable size of the hole created in the mirror center due to the self-injection process has a destructive effect on the reflection efficiency. Finally, an efficient reflection can be obtained by controlling the delay time. The optimal delay for arbitrary parameters of the laser and plasma depends on the region in which the most efficient flying mirrors are created by the mutual interaction of the plasma density and the driver amplitude along with considering the pulse situation when reaching the mirror. By analyzing the electron phase space, it was found that the velocity of density spikes changes rapidly when passing through the plasma. The higher speed of the electrons of the mirrors contributing to the source reflection leads to the production of the higher upshifted frequency peak in different source delays.
The filamentation effect in short pulse amplification by strong-coupling stimulated Brillouin sca... more The filamentation effect in short pulse amplification by strong-coupling stimulated Brillouin scattering Physics of Plasmas 26, 093102 (2019);
The nonlinear dynamics of filamentation instability in a weakly ionized current-carrying plasma i... more The nonlinear dynamics of filamentation instability in a weakly ionized current-carrying plasma in the diffusion frequency region is studied using particle in cell simulation. The effects of electron thermal motion and ion-neutral collision on the evolution of this instability in the nonlinear stage of the filaments coalescence are discussed. It is found that the coalescence of the current filaments is enhanced by increasing the temperature and is delayed by increasing the collision frequency.
The nonlinear dynamics of low frequency Buneman instability in a current-driven cold unmagnetized... more The nonlinear dynamics of low frequency Buneman instability in a current-driven cold unmagnetized plasma are studied using particle in cell simulation. Simulations of the Buneman instability show that the electron density profile has sharp peaks and the amplitude of the peaks changes with time. Also, the nonlinear evolution of this instability and saturation time is investigated by the time variation of the electric potential energy in the plasma. Moreover, the electron trapping phenomena and the formation of phase space electron holes are presented by considering the phase space diagram and electron distribution function. Finally, the ion mass effect on saturation time is investigated and it is found that the saturation time increases by increasing the ion mass and the saturation level is not very sensitive to the ion mass.
The nonlinear dynamics of low frequency Buneman instability in a current-driven cold unmagnetized... more The nonlinear dynamics of low frequency Buneman instability in a current-driven cold unmagnetized plasma are studied using particle in cell simulation. Simulations of the Buneman instability show that the electron density profile has sharp peaks and the amplitude of the peaks changes with time. Also, the nonlinear evolution of this instability and saturation time is investigated by the time variation of the electric potential energy in the plasma. Moreover, the electron trapping phenomena and the formation of phase space electron holes are presented by considering the phase space diagram and electron distribution function. Finally, the ion mass effect on saturation time is investigated and it is found that the saturation time increases by increasing the ion mass and the saturation level is not very sensitive to the ion mass.
The nonlinear dynamics of filamentation instability in a weakly ionized current-carrying plasma i... more The nonlinear dynamics of filamentation instability in a weakly ionized current-carrying plasma in the diffusion frequency region is studied using particle in cell simulation. The effects of electron thermal motion and ion-neutral collision on the evolution of this instability in the nonlinear stage of the filaments coalescence are discussed. It is found that the coalescence of the current filaments is enhanced by increasing the temperature and is delayed by increasing the collision frequency.
The attosecond pulse generation by the interaction of two counterpropagating ultrashort laser pul... more The attosecond pulse generation by the interaction of two counterpropagating ultrashort laser pulses with near-critical density plasma is simulated using two-dimensional particle in the cell method. Results of the simulations showed the flying mirror properties such as density and shape change, while moving through the plasma, behind the intense driver laser. We investigated the effects of the mirror features on the produced attosecond pulse intensity by setting various delay times between the driver and source pulses so that the source encounters the mirror at different points. It is demonstrated that the higher density of the mirror, particularly in its center (due to the Gaussian transverse profile of the source), in addition to its suitable curvature and surface smoothness, results in a more intense reflection. Moreover, a considerable size of the hole created in the mirror center due to the self-injection process has a destructive effect on the reflection efficiency. Finally, an efficient reflection can be obtained by controlling the delay time. The optimal delay for arbitrary parameters of the laser and plasma depends on the region in which the most efficient flying mirrors are created by the mutual interaction of the plasma density and the driver amplitude along with considering the pulse situation when reaching the mirror. By analyzing the electron phase space, it was found that the velocity of density spikes changes rapidly when passing through the plasma. The higher speed of the electrons of the mirrors contributing to the source reflection leads to the production of the higher upshifted frequency peak in different source delays.
The filamentation effect in short pulse amplification by strong-coupling stimulated Brillouin sca... more The filamentation effect in short pulse amplification by strong-coupling stimulated Brillouin scattering Physics of Plasmas 26, 093102 (2019);
The nonlinear dynamics of filamentation instability in a weakly ionized current-carrying plasma i... more The nonlinear dynamics of filamentation instability in a weakly ionized current-carrying plasma in the diffusion frequency region is studied using particle in cell simulation. The effects of electron thermal motion and ion-neutral collision on the evolution of this instability in the nonlinear stage of the filaments coalescence are discussed. It is found that the coalescence of the current filaments is enhanced by increasing the temperature and is delayed by increasing the collision frequency.
The nonlinear dynamics of low frequency Buneman instability in a current-driven cold unmagnetized... more The nonlinear dynamics of low frequency Buneman instability in a current-driven cold unmagnetized plasma are studied using particle in cell simulation. Simulations of the Buneman instability show that the electron density profile has sharp peaks and the amplitude of the peaks changes with time. Also, the nonlinear evolution of this instability and saturation time is investigated by the time variation of the electric potential energy in the plasma. Moreover, the electron trapping phenomena and the formation of phase space electron holes are presented by considering the phase space diagram and electron distribution function. Finally, the ion mass effect on saturation time is investigated and it is found that the saturation time increases by increasing the ion mass and the saturation level is not very sensitive to the ion mass.
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Papers by Davood Komaizi