An intense radiation field can modify plasma properties and the corresponding refractive index and lead to nonlinear propagation effects such as self-focusing. We estimate the corresponding effects in pair plasmas for circularly polarized waves, in both unmagnetized and strongly magnetically dominated cases. First, in the unmagnetized pair plasma the ponderomotive force does not lead to charge separation but to density depletion. Second, for astrophysically relevant plasmas of pulsar magnetospheres [and possible loci of fast radio bursts (FRBs)], where the cyclotron frequency ${\omega }_B$ dominates over the plasma frequency ${\omega }_p$ and the frequency of the electromagnetic wave ${\omega }_B\gg {\omega }_p,\omega$, we show that (i) there is virtually no nonlinearity due to changing effective mass in the field of the wave; (ii) the ponderomotive force is $F_p^{\left(B\right)}=-m_e{c}^2/4B_0^2\mathbf{\nabla }{E}^2$, which is reduced by a factor ${(\omega /{\omega }_B)}^2$ if compared to the unmagnetized case ($B_0$ is the external magnetic field and $E$ is the electric field of the wave); and (iii) for a radiation beam propagating along a constant magnetic field in the pair plasma with density $n_{\pm }$, the ponderomotive force leads to the appearance of circular currents that lead to a decrease of the field within the beam by a factor $\mathrm{\Delta }B/B_0=2\pi n_{\pm }{m}_e{c}^2{E}^2/B_0^4$. Applications to the physics of FRBs are discussed; we conclude that for the parameters of FRBs, the dominant magnetic field completely suppresses nonlinear self-focusing or filamentation.

中文翻译：

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强磁化对等离子体中的非线性自聚焦。

强烈的辐射场会改变等离子体特性和相应的折射率，并导致非线性传播效应，例如自聚焦。在未磁化和强磁控制的情况下，我们估计圆极化波对等离子体中的相应影响。首先，在未磁化的一对等离子体中，质动力不导致电荷分离，而是导致密度耗尽。其次，对于脉冲星磁层的天体相关等离子体[以及快速无线电脉冲串（FRB）的可能轨迹]，其中回旋加速器频率${\omega }_{乙}$ 在等离子体频率上占主导地位 ${\omega }_p$ 和电磁波的频率 ${\omega }_{乙}\gg {\omega }_p，\omega$，我们证明（i）由于波场中有效质量的变化，实际上没有非线性；（ii）质动力是$F_p^{（乙）}=-{米}_{Ë}{C}^2/4{乙}_0^2\mathbf{\nabla }{Ë}^2$，减少了一个因子 ${（\omega /{\omega }_{乙}）}^2$ 如果与未磁化的情况相比（${乙}_0$ 是外部磁场， $Ë$是波的电场）；（iii）对于在等离子体对中沿恒定磁场传播的辐射束，其密度${ñ}_{\pm }$，动磁力导致出现环形电流，从而导致光束内的磁场减小一个因子 $\mathrm{\Delta }乙/{乙}_0=2\pi {ñ}_{\pm }{米}_{Ë}{C}^2{Ë}^2/{乙}_0^4$。讨论了FRB的物理应用。我们得出的结论是，对于FRB的参数，主磁场完全抑制了非线性自聚焦或细丝化。