Unraveling the Link Between Radio-frequency Wave Propagation and High Ionization Efficiency of Helicon Waves

这个研究项目的重点是为未来的粒子加速器应用产生非常均匀的等离子体的物理学。等离子体是物质的第四种状态，在许多科学和工业应用中具有重要意义，其中之一是作为下一代粒子加速器的介质。等离子体的电学特性允许高加速电场梯度，比现有的基于固体的粒子加速器高100倍。这可以转化为更紧凑、更有能量、更便宜的加速器。在瑞士日内瓦的欧洲核子研究中心，AWAKE项目旨在使用等离子体柱作为基于尾流场加速概念的下一代电子加速器的介质。这笔拨款将支持旨在提高对等离子体柱如何形成和调整以满足AWAKE加速器应用要求的理解的研究。对这种等离子体源的理解也与其他各种应用直接相关，例如工业和生命科学中的等离子体处理，基于聚变的中子源的等离子体产生，以及天体物理等离子体湍流风洞实验的发展。在这个项目中产生等离子体的具体方法是所谓的螺旋波。这些是哨声状态下的射频波，以可靠地产生高密度的磁化等离子体和非常高的电离分数而闻名。在10^3高斯的磁场范围内，这些波通常被称为螺旋子。它们的特点是从电感耦合、低密度和低电离状态过渡到高密度和几乎完全的气体电离状态。这种向螺旋态的转变和在这种状态下的电离动力学还没有被完全理解。这与等离子体作为粒子加速介质的应用有关。这种应用要求在加速粒子束路径方向上的等离子体密度具有前所未有的均匀性。本研究的目的是解决螺旋跃迁，并了解跃迁期间和之后不久的电离动力学。等离子体诊断将基于分析等离子体发出的光来了解等离子体的轴向均匀性，并使用主动的局部气体注入方法来控制轴向等离子体密度。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The focus of this research project is on the physics of generating very uniform plasmas for future particle accelerator applications. Plasmas, the fourth state of matter, are of importance for many science and industrial applications, one of which is as a medium for next generation particle accelerators. The electrical features of a plasma allow for high accelerating electric field gradients which are up to a factor of a hundred greater than in existing solid-state-based particle accelerators. This can translate into much more compact, energetic, and cheap accelerators. At CERN in Geneva, Switzerland, the AWAKE project aims to use a plasma column as a medium for a next generation electron accelerator based on the wakefield acceleration concept. This grant will support research aimed at improving the understanding of how a plasma column can be formed and tuned for the requirements in the AWAKE accelerator application. The understanding of such plasma sources is also of direct relevance to a variety of other applications, such as plasma processing in industry and life-sciences, plasma generation for fusion-based neutron sources, and development of a wind-tunnel experiment for astrophysical plasma turbulence.The specific method used for plasma generation in this project is the so-called Helicon wave. These are radio-frequency waves in the whistler regime, known broadly for reliable generation of magnetized plasmas at high density with very high ionization fractions. In the magnetic field regimes of 10^3 Gauss, these waves are canonically called Helicons. They are characterized by a transition from an inductively coupled, low density and low ionization regime into a regime of high density and almost complete gas ionization. This transition into the helicon regime and the ionization dynamics in this regime are not yet fully understood. This is linked to the application of a plasma as the medium for particle acceleration. This application requires unprecedented levels of homogeneity in the plasma density in the direction of the accelerated particle beam path. The goal of this research is to resolve the helicon transition and understand the ionization dynamics during the transition and shortly afterwards. Plasma diagnostics based on analyzing the light emitted from the plasma will be used to understand the plasma axial homogeneity and methods of active, local gas injection will be used to gain control of the axial plasma density.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.