Collaborative Research: Understanding Sheaths and Pre-Sheaths in Magnetized and Unmagnetized Plasmas

这个项目将研究等离子体近表面层的物理性质，即等离子体鞘，它是当固体被放置到等离子体中时形成的。等离子体是由自由离子和电子组成的气体；它们在宇宙中大量存在，有许多工业应用，是受控聚变研究的关键组成部分。制造计算机微处理器所需的制造步骤中，近一半使用了等离子体。等离子体与材料的相互作用取决于靠近表面的区域，称为等离子体鞘。更好地了解鞘将导致微处理器制造的改进，并可能是实现受控融合的关键。这项研究中使用的桌面实验也是理想的，并将极大地有助于培训学生在等离子体物理和其他STEM领域。拟议的新的和继续的实验旨在确定鞘和相关的预鞘的基本性质，这些预鞘可以加速离子进入鞘。将讨论的具体问题是：1.新发现的不稳定性增强的碰撞摩擦的细节是什么？2.离子速度分布函数(IVDF)沿前壁和鞘边缘的各向异性发生了什么？3.为什么横向IVDF的实验结果与模拟结果不同？4.当三种弱碰撞等离子体中的离子具有类似的密度时，它们是否都在系统音速下损失？5.是否存在与离子-中性碰撞和倾斜磁场相关的单独的预生路径？6.介电和混合边界的鞘和预生路径与导体上的不同？7.当一个小电极偏置到等离子体电位时，鞘是否消失？威斯康星大学麦迪逊分校和圣地亚哥大学将对这些现象进行协调研究。实验将确定健康前和鞘内等离子体的电势分布，以及与离子加速相关的结果IVDF。大多数实验将在麦迪逊进行，由圆周率教授诺亚·赫什科维茨领导。激光诱导荧光(LIF)诊断开发将在两个校区进行，并由联合PI教授Greg Severn领导。等离子体参数将通过两种或两种以上技术来确定，例如，发射探头、激光诱导荧光、朗缪尔探头、离子声波测量和光学发射光谱的组合。实验将采用目前正在运行的热丝多偶极子源、电容源、感应源和螺旋源。

This project will investigate the physical properties of a near-surface layer of a plasma, a plasma sheath, which forms when a solid body is placed into a plasma. Plasmas are gases consisting of free ions and electrons; they are abundant in the universe, have many industrial applications and are the critical component of controlled fusion research. Nearly a half of the manufacturing steps necessary to fabricate a computer microprocessor employ plasmas. The interaction of plasmas with materials depends on the region close to the surfaces known as the plasma sheath. Better understanding of sheaths will lead to improved microprocessor fabrications and might be essential in achieving controlled fusion. The tabletop experiments employed in this study are also ideal for, and will greatly contribute to, training of students in the field of plasma physics and other STEM fields. Proposed new and continuing experiments are aimed at establishing the basic properties of sheaths and associated presheaths, which accelerate ions to the sheath. The specific questions that will be addressed are: 1. What are the details of the newly recognized instability-enhanced collisional friction? 2. What happens to the anisotropy of ion velocity distribution functions (IVDFs) along the presheath and at the sheath-edge? 3. Why do experimental transverse IVDF results differ from simulations? 4. Are the ions in three species weakly collisional plasmas all lost at the system sound velocity when they have comparable densities? 5. Are there separate presheaths associated with ion-neutral collisions and oblique magnetic fields? 6. How do sheaths and presheaths at dielectric and mixed boundaries differ from those at conductors? 7. Does the sheath disappear or not when a small electrode is biased to the plasma potential? Coordinated studies of these phenomena will be carried out at the University of Wisconsin-Madison and the University of San Diego. Experiments will determine the presheath and sheath plasma potential profiles and the resulting IVDFs associated with ion acceleration. Most of the experiments will be carried out in Madison and led by the PI Prof. Noah Hershkowitz. Laser induced fluorescence (LIF) diagnostic development will be carried out on both campuses and led by the Co-PI Prof. Greg Severn. Plasma parameters will be determined with two or more techniques, e.g. combinations of emissive probes, LIF, Langmuir probes, ion acoustic wave measurements, and optical emission spectroscopy. Experiments will employ hot filament multi-dipole, capacitive, inductive, and helicon sources currently in operation.