Plasma sheaths characterized by electrons with relativistic energies and far from thermodynamic equilibrium are governed by a rich and largely unexplored physics. A reliable kinetic description of relativistic non-equilibrium plasma sheaths—besides its interest from a fundamental point of view—is crucial to many application, from controlled nuclear fusion to laser-driven particle acceleration. Sheath models proposed in the literature adopt either relativistic equilibrium distribution functions or non-relativistic non-equilibrium distribution functions, making it impossible to properly capture the physics involved when both relativistic and non-equilibrium effects are important. Here we tackle this issue by solving the electrostatic Vlasov–Poisson equations with a new class of fully-relativistic distribution functions that can describe non-equilibrium features via a real scalar parameter. After having discussed the general properties of the distribution functions and the resulting plasma sheath model, we establish an approach to investigate the effect of non-equilibrium solely. Then, we apply our approach to describe laser–plasma ion acceleration in the target normal sheath acceleration scheme. Results show how different degrees of non-equilibrium lead to the formation of sheaths with significantly different features, thereby having a relevant impact on the ion acceleration process. We believe that this approach can offer a deeper understanding of relativistic plasma sheaths, opening new perspectives in view of their applications.

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相对论等离子体鞘模型中的非平衡效应

以具有相对论能量且远离热力学平衡的电子为特征的等离子体鞘由丰富且大部分未探索的物理学控制。相对论非平衡等离子体鞘的可靠动力学描述——除了从基本观点来看它的兴趣之外——对于许多应用至关重要，从受控核聚变到激光驱动的粒子加速。文献中提出的鞘模型采用相对论平衡分布函数或非相对论非平衡分布函数，因此当相对论和非平衡效应都很重要时，无法正确捕捉所涉及的物理。在这里，我们通过使用一类新的完全相对论分布函数求解静电 Vlasov-Poisson 方程来解决这个问题，这些函数可以通过实标量参数描述非平衡特征。在讨论了分布函数的一般特性和由此产生的等离子体鞘模型后，我们建立了一种方法来单独研究非平衡的影响。然后，我们应用我们的方法来描述目标法向鞘加速方案中的激光-等离子体离子加速。结果显示了不同程度的非平衡如何导致形成具有显着不同特征的鞘，从而对离子加速过程产生相关影响。我们相信这种方法可以提供对相对论等离子体鞘的更深入理解，