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

该项目将研究等离子体近表层的物理特性，即等离子体鞘层，当固体被放入等离子体中时形成。等离子体是由自由离子和电子组成的气体；它们在宇宙中丰富，有许多工业应用，是可控核聚变研究的关键组成部分。制造计算机微处理器所需的近一半的制造步骤都要用到等离子体。等离子体与物质的相互作用取决于靠近表面的区域，即等离子体鞘层。更好地了解鞘层将有助于改进微处理器的制造，并且可能对实现可控聚变至关重要。本研究中使用的桌面实验对于等离子体物理和其他STEM领域的学生训练也是理想的，并且将大大有助于。提出了新的和持续的实验，旨在建立鞘和相关的预鞘的基本性质，加速离子鞘。将讨论的具体问题有：1。新认识到的不稳定增强的碰撞摩擦的细节是什么？2. 沿鞘前和鞘边的离子速度分布函数（ivdf）的各向异性发生了什么变化？3. 为什么横向IVDF实验结果与模拟结果不同？4. 当密度相当时，三种弱碰撞等离子体中的离子是否在系统声速下全部丢失？5. 是否存在与离子中性碰撞和斜磁场相关的单独预鞘？6. 介电和混合边界处的护套和预护套与导体处的护套有何不同？7. 当一个小电极偏向于等离子体电位时，鞘层是否消失？对这些现象的协调研究将在威斯康星大学麦迪逊分校和圣地亚哥大学进行。实验将确定鞘前和鞘内等离子体电位分布以及由此产生的与离子加速相关的ivdf。大部分实验将在麦迪逊进行，并由PI教授Noah Hershkowitz领导。激光诱导荧光（LIF）诊断开发将在两个校区进行，并由联合主任Greg Severn教授领导。等离子体参数将通过两种或两种以上的技术来确定，例如发射探针、LIF、Langmuir探针、离子声波测量和光学发射光谱的组合。实验将采用热丝多偶极子，电容，电感，和螺旋源目前的操作。

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.