The all pervading magnetic field in nature has aroused great curiosity and spawned many efforts to understand its generation. We propose, simulate, and experimentally demonstrate another mechanism of long-scale magnetic field generation in the context of a laser-plasma interaction. It relies on two realistic features, namely the finite size of the laser generated electron beam and an initial current imbalance. It is shown that magnetic fields of scale lengths comparable to the transverse beam dimension, are generated much before the onset of conventional instabilities associated with the beam-plasma system. This is due to radiative leakage at the boundaries of the finite beam, wherein even a small but finite current imbalance plays the crucial role of a radiative antenna. These features have been absent in simulations and theoretical analyses using the periodic boundary condition.

中文翻译：

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束流-等离子体相互作用中产生宏观磁场的边界驱动非常规机理

自然界中无处不在的磁场引起了人们的极大好奇，并催生了许多努力来了解它的产生。我们提出，模拟和实验证明在激光-等离子体相互作用的上下文中产生长尺度磁场的另一种机制。它依赖于两个现实的特征，即激光产生的电子束的有限大小和初始电流不平衡。结果表明，在与束-等离子体系统有关的常规不稳定性开始之前，就产生了与横束尺寸相当的标度长度的磁场。这是由于有限波束边界处的辐射泄漏引起的，其中即使很小但有限的电流不平衡也起着辐射天线的关键作用。