Stochastic behavior of electrons in high intensity laser–plasma interaction

Abstract

The stochastic behavior of electrons during the interaction of an intense short laser pulse with under-dense plasma is investigated by employing a fully kinetic 1D-3V particle-in-cell (PIC) simulation. The development of chaos in the involved nonlinear regime and in the presence of plasma space charge is examined. Though the electron Lagrangian is extremely complicated in this case, our analyses suggest some potential ways for chaos development. In this regard, our simulation results show that chaotic motion can develop in three different ways. When the space charge field is weak, the scattered fields can provide the necessary condition for chaos to occur. When a strong space charge field is presented, the creation of chaos is initiated by wave breaking. The third procedure for creating chaos originates from the inhomogeneity of the density on the vacuum-plasma surface. In this case, a new electrostatic mode without any phase relation with the space charge electrostatic mode is generated.

Electron energy spectrum in the field‐ionized plasma

“…In the following, as seen in Figure 7, the treatment of the electric field and the phase space curves are different by employing the field-ionized and the pre-plasma conditions. The results of the previous research studies [17,18] show that for the pulses with smooth rise-time, the backscattered Raman radiations are generated in the early times of interaction. In this case, if the amplitude of these Raman backscattering radiations meets the Mendonca threshold limit a 1 a 2 = 1∕16, the chaos occurs.…”

“…In fact, with the increase in density in pre-plasma, the chaos do not occur due to the increase in the space charge electric field. [17]…”

“…The last mechanism is related to the stochastic acceleration of the electrons in the presence of two counter-propagating laser fields. [11][12][13][14][15][16][17][18] It was found earlier from particle-in-cell (PIC) simulations that through this scheme, energetic electrons can be generated higher than the ponderomotive potential of the first laser pulse. [13,14] In another work, it was shown that in sufficiently long laser pulses, the backward Raman-scattered radiation can act as a second electromagnetic radiation.…”

“…Therefore, energetic electrons are produced through the stochastic mechanism [15] in interaction of the intense laser pulse with under-dense plasma. Khalilzadeh et al [16][17][18] revealed that the plasma behaviour, the pulse evolution, and the acceleration mechanisms are strongly dependent on the pulse shape, so, for pulses with different rise-times, there are different acceleration mechanisms to energize electrons. In this work, it was indicated that in the interaction of the smooth rising laser pulses with the plasma, because of the long length of the pulse rise-time duration, a strong ponderomotive force cannot be produced and parametric instabilities such as Raman backward scattering can grow from a noise level and reach to a specified level.…”

Numerical investigation of plasma heating during the entrance of an intense short laser pulse into a density profile

“…An investigation of stochastic acceleration resulting from nonlinear wave breaking at the vacuum-plasma interface has been published by the authors of [21]. In their newest research [22], they considered the progression of chaotic motion in plasma and mentioned that chaotic motion could emerge from the plasma density inhomogeneity at the vacuum-plasma interface. Although many scientists have performed a significant amount of research, several crucial aspects still deserve further study, and the exact mechanism of the impact of pre-plasma in electron acceleration and plasma heating remains unclear.…”