Laser-driven tin plasmas are driving new-generation nanolithography as sources of extreme ultraviolet (EUV) radiation centered at 13.5 nm. A major challenge facing industrial EUV source development is predicting energetic ion debris produced during the plasma expansion that may damage the sensitive EUV channeling multilayer optics. Gaining a detailed understanding of the plasma dynamics and ion acceleration mechanisms in these sources could provide critical insights for designing debris mitigation strategies in future high-power EUV sources. We develop a fully kinetic model of tin-EUV sources using one-dimensional particle-in-cell simulations to study ion debris acceleration, which will be valuable for cross-validation of radiation-hydrodynamic simulations. An inverse-bremsstrahlung heating operator is used to model the interaction of a tin target with an Nd:YAG laser, and thermal conduction is included through a Monte Carlo Coulomb collision operator. While the large-scale evolution is in reasonable agreement with analogous hydrodynamic simulations, the significant timescale for collisional equilibration between electrons and ions allows for the development of prominent two-temperature features. A collimated flow of energetic ions is produced with a spectrum that is significantly enhanced at high energies compared to fluid simulations. The dominant acceleration mechanism is found to be a large-scale electric field supported mainly by the electron pressure gradient, which is enhanced in the kinetic simulations due to the increased electron temperature. We discuss the implications of these results for future modeling of tin-EUV sources and the development of debris mitigation schemes.

中文翻译：

---

激光驱动锡等离子体 EUV 源中高能离子碎片的加速机制

激光驱动的锡等离子体作为以 13.5 nm 为中心的极紫外 (EUV) 辐射源，正在推动新一代纳米光刻技术的发展。工业 EUV 源开发面临的主要挑战是预测等离子体膨胀过程中产生的高能离子碎片，这些碎片可能会损坏敏感的 EUV 通道多层光学器件。详细了解这些源中的等离子体动力学和离子加速机制可以为设计未来高功率 EUV 源中的碎片缓解策略提供重要的见解。我们开发了锡-EUV源的全动力学模型，使用一维粒子内细胞模拟来研究离子碎片加速，这对于辐射-流体动力学模拟的交叉验证非常有价值。逆轫致辐射加热算子用于模拟锡靶与 Nd:YAG 激光器的相互作用，并通过蒙特卡罗库仑碰撞算子包含热传导。虽然大规模演化与类似的流体动力学模拟相当一致，但电子和离子之间的碰撞平衡的重要时间尺度允许显着的双温度特征的发展。与流体模拟相比，产生的高能离子准直流的光谱在高能量下显着增强。研究发现，主要的加速机制是主要由电子压力梯度支持的大尺度电场，由于电子温度的升高，电子压力梯度在动力学模拟中得到增强。我们讨论了这些结果对未来锡 EUV 源建模和碎片减缓方案开发的影响。