Ion dynamics driven by a strongly nonlinear plasma wake

In plasma wakefield accelerators, the wave excited in the plasma eventually breaks and leaves behind slowly changing fields and currents that perturb the ion density background. We study this process numerically using the example of a FACET experiment where the wave is excited by an electron bunch in the bubble regime in a radially bounded plasma. Four physical effects underlie the dynamics of ions: (1) attraction of ions toward the axis by the fields of the driver and the wave, resulting in formation of a density peak, (2) generation of ion-acoustic solitons following the decay of the density peak, (3) positive plasma charging after wave breaking, leading to acceleration of some ions in the radial direction, and (4) plasma pinching by the current generated during the wavebreaking. Interplay of these effects result in formation of various radial density profiles, which are difficult to produce in any other way.

Head-on collision of two ion-acoustic solitons in pair-ion plasmas with nonthermal electrons featuring Tsallis distribution

The head-on collision between two ion-acoustic solitons (IASs) is studied in pair ions plasmas with hybrid Cairns–Tsallis-distributed electrons. The chosen model is inspired from the experimental studies of Ichiki et al. [Phys. Plasmas 8, 4275 (2001)]. The extended Poincaré–Lighthill–Kuo (PLK) method is employed to obtain the phase shift due to the IASs collision. Both analytical and numerical results reveal that the magnitude of the phase shift is significantly affected by the nonthermal and nonextensive parameters (α and q), the number density ratios (μ and υ) as well as the mass ratio σ. For a given mass ratio σ ≃ 0.27 $\sigma \simeq 0.27$ (Ar+, SF 6 − ${\text{SF}}_{6}^{-}$ ), the magnitude of the phase shift Δ Q ( 0 ) ${\Delta}{Q}^{\left(0\right)}$ decreases slightly (increases) with the increase of q (α). The effect of α on Δ Q ( 0 ) ${\Delta}{Q}^{\left(0\right)}$ is more noticeable in the superextensive distribution case (q < 1). As σ increases [ σ ≃ 0.89 $\sigma \simeq 0.89$ (Xe+, SF 6 − ${\text{SF}}_{6}^{-}$ )], the phase shift becomes wider. In other terms, the phase shift was found to be larger under the effect of higher densities of the negative ions. Our findings should be useful for understanding the dynamics of IA solitons’ head-on collision in space environments [namely, D-regions ( H + ${\text{H}}^{+}$ , O 2 − ${\text{O}}_{2}^{-}$ ) and F-regions (H+, H−) of the Earth’s ionosphere] and in laboratory double pair plasmas [namely, fullerene (C+, C−) and laboratory experiment (Ar+, F−)].

Arbitrary amplitude ion acoustic solitons, double layers and supersolitons in a collisionless magnetized plasma consisting of non-thermal and isothermal electrons

Using Sagdeev pseudo-potential technique, we have studied the arbitrary amplitude ion acoustic solitons, double layers and supersolitons in a collisionless plasma consisting of adiabatic warm ions, non-thermal hot electrons and isothermal cold electrons immersed in an external uniform static magnetic field. We have used the phase portraits of the dynamical system describing the non-linear behaviour of ion acoustic waves to confirm the existence of different solitary structures. We have found that the system supports (a) positive potential solitons, (b) negative potential solitons, (c) coexistence of both positive and negative potential solitons, (d) negative potential double layers, (e) negative potential supersolitons and (f) positive potential supersolitons. Again, we have seen that the amplitude of the positive potential solitons decreases or increases with increasing n ch according to whether 0 < n c h < n c h ( c ) $0{< }{n}_{ch}{< }{n}_{ch}^{\left(c\right)}$ or n c h ( c ) < n c h ≤ 1 ${n}_{ch}^{\left(c\right)}{< }{n}_{ch}\le 1$ , where n c h ${n}_{ch}$ is the ratio of isothermal cold and non-thermal hot electron number densities, and n c h ( c ) ${n}_{ch}^{\left(c\right)}$ is a critical value of n ch . Also, we have seen that the amplitude of the positive potential solitons decreases with increasing β e , where β e is the non-thermal parameter. We have also investigated the transition of different negative potential solitary structures: negative potential soliton (before the formation of negative potential double layer) → negative potential double layer → negative potential supersoliton → negative potential soliton (after the formation of negative potential double layer) by considering the variation of θ only, where θ is angle between the direction of the external uniform static magnetic field and the direction of propagation of the ion acoustic wave.