强交叉电磁场中的磁场屏蔽
Magnetic field screening in strong crossed electromagnetic fields
摘要：
我们考虑交叉电场和磁场$\left(\vec{B}=B\,\hat{z},~\vec{E}=E\,\hat{y}\right)$，与$E/B<1$，在存在一些初始数量的$e^{\pm}$对。这里我们不讨论这些初始电子对的产生机制。电场将电子对加速到高能量，从而辐射出高能量的同步加速器光子。这些光子通过磁对产生过程（MPP）（即$γ+B\rightarrow e^{+}+e^{-}$）与磁场相互作用，产生额外的磁对。我们在这里表明，所有的运动对周围的磁场线产生的电流，感应出一个磁场，屏蔽了最初的。例如，对于初始数量的对$N_{\pm,0}=10^{10}$，$10^{12}$ G的初始磁场可以减小百分之几。筛选发生在短时间尺度$10^{-21}\leq t \leq 10^{-15}$中，即在粒子加速时间尺度等于同步加速器冷却时间尺度之前。本简化模型指出了导致强磁场屏蔽的物理条件。为了评估这种现象发生在特定的天体物理源，如射电或伽马射线暴，该模型可以扩展到评估不同的几何形状的电场和磁场，量子效应在超临界领域，和特定的机制的生产，分布，和多重性的$e^{-}e^{+}$对。
英文摘要：
We consider crossed electric and a magnetic fields $\left(\vec{B}=B\,\hat{z},~\vec{E}=E\,\hat{y}\right)$, with $E/B<1$, in presence of some initial number of $e^{\pm}$ pairs. We do not discuss here the mechanism of generation of these initial pairs. The electric field accelerates the pairs to high-energies thereby radiating high-energy synchrotron photons. These photons interact with the magnetic field via magnetic pair production process (MPP), i.e. $γ+B\rightarrow e^{+}+e^{-}$, producing additional pairs. We here show that the motion of all the pairs around the magnetic field lines generates a current that induces a magnetic field that shields the initial one. For instance, for an initial number of pairs $N_{\pm,0}=10^{10}$, an initial magnetic field of $10^{12}$ G can be reduced of a few percent. The screening occurs in the short timescales $10^{-21}\leq t \leq 10^{-15}$ s, i.e. before the particle acceleration timescale equals the synchrotron cooling timescale. The present simplified model indicates the physical conditions leading to the screening of strong magnetic fields. To assess the occurrence of this phenomenon in specific astrophysical sources, e.g. pulsars or gamma-ray bursts, the model can be extended to evaluate different geometries of the electric and magnetic fields, quantum effects in overcritical fields, and specific mechanisms for the production, distribution, and multiplicity of the $e^{-}e^{+}$ pairs.
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