International Research Fellowship Program: Particle Tracking and Anomalous Statistics in a Basic Plasma Physics Experiment

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。国际研究奖学金项目使美国科学家和工程师能够在国外进行9至24个月的研究。该计划的奖励为联合研究提供了机会，并利用独特或互补的设施、专业知识和国外的实验条件。该奖项将支持Kyle B. Gustafson博士与瑞士联邦理工学院（Ecole Polytech Federale）的Paolo Ricci博士进行为期24个月的研究。等离子体湍流在许多情况下都很重要，从聚变能研究中的热量和粒子的传输到天体物理等离子体的加热。目前人们感兴趣的一个尚未解决的问题是，湍流输运是否一般可以用由布朗随机游走假设导出的标准扩散方程来描述。用连续时间随机游走和分数扩散方程对输运的精细描述最近被应用于等离子体湍流的模拟。例如，连续时间随机行走允许步长和等待时间的分布是非高斯分布，可能具有幂律依赖性。分数扩散方程在扩散方程的推广中使用非局部积分微分算子描述粒子系综的宏观传播。到目前为止，结果是有希望的，但与实际实验和观察的比较受到诊断可能性的限制。瑞士洛桑的国际研究博士后奖学金旨在促进在基本等离子体实验中寻找异常或非布朗输运迹象，同时在实验模拟中进行研究。这种方法将有助于确认或否认非布朗输运的相关性，在一个基本的实验，鱼雷，与前所未有的诊断工具集。它还将根据来自实验的高分辨率数据验证和验证模拟，同时使用模拟来指导实验操作的重点。我们使用的诊断包括一个大型朗缪尔探针阵列，快速离子注入和气体喷涌成像与快速相机。模拟基于三维流体方程，在生成的场中具有被动粒子跟踪。我们解决以下问题。粒子的能量、质量和电荷如何影响描述这些粒子输运的非布朗模型的相关性？器件的参数，如场拓扑和温度和密度梯度，如何影响非布朗输运？计算结果和非布朗输运模型在多大程度上解释了鱼雷在各种条件下的高分辨率数据？这些比较如何推广？位于洛桑的等离子体物理研究中心（CRPP）是聚变和工业等离子体物理研究的主要机构。基本的环形装置称为鱼雷具有一套完全独特的诊断，特别是研究磁化湍流中的粒子运动。鱼雷的模拟已经开发出来，并准备用于粒子跟踪研究。CRPP的计算设施为这一目的装备精良。这项研究与欧洲规模庞大且不断增长的等离子体物理研究，包括具有里程碑意义的ITER实验，形成了协同效应。这些关于等离子体微湍流的详细实验结果将与美国的各种团体分享。非布朗输运研究的结果将与湍流热、动量和湍流加热的输运有关。在天体物理学中，将对粒子的能量和加热有更好的理解。核聚变能的研究主要依赖于粒子输运的正确表征，因为一个有效的机器必须在核心有很大的能量密度。本研究将通过对鱼雷的数据分析和仿真来改进这一特性。

0853498GustafsonThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four-month research fellowship by Dr. Kyle B. Gustafson to work with Dr. Paolo Ricci at Ecole Polytech Federale in Switzerland.Plasma turbulence is important in many contexts, from transport of heat and particles in fusion energy research to heating of astrophysical plasmas. An unresolved question of current interest is whether turbulent transport can generally be described using the standard diffusion equation derived from the assumptions of a Brownian random walk. Subtler descriptions of transport in terms of continuous time random walks and fractional diffusion equations have recently been applied to simulations of plasma turbulence. For example, continuous time random walks allow the distribution of step sizes and waiting times for the walkers to be non-Gaussian, possibly with power law dependence. Fractional diffusion equations describe the macroscopic propagation of an ensemble of particles using nonlocal, integro-differential operators in a generalization of the diffusion equation. The results so far have been promising, but comparison with actual experiment and observation has been limited by diagnostic possibilities. This International Research Postdoctoral Fellowship in Lausanne, Switzerland is intended to facilitate a search for anomalous, or non-Brownian, transport indications in a basic plasma experiment and, simultaneously, in simulations of the experiment. This approach will help confirm or deny the relevance of non-Brownian transport in a fundamental experiment, TORPEX, with an unprecedented set of diagnostic tools. It will also verify and validate simulations against highly resolved data from the experiment, while using the simulations to guide the focus of the experimental operation. We use diagnostics including a large Langmuir probe array, fast-ion injection and gas puff imaging with a fast camera. Simulations are based on three-dimensional fluid equations with passive particle tracking in the generated fields. We address the following questions. How do the energy, mass and charge of particles affect the relevance of non-Brownian models for describing transport of those particles? How do the parameters of the device, such as field topology and gradients of temperature and density, affect non-Brownian transport? To what extent do computational results and non-Brownian transport models explain the high-resolution data from TORPEX in various conditions and how can these comparisons be generalized?The Centre de Recherches en Physique des Plasmas (CRPP) in Lausanne is a major facility for fusion and industrial plasma physics research. The basic toroidal device called TORPEX possesses a completely unique set of diagnostics especially for studying the movement of particles in magnetized turbulence. Simulations of TORPEX have been developed and are ready to be used for particle tracking studies. The CRPP computational facilities are well-equipped for this purpose. This research synergizes with the large and growing plasma physics efforts in Europe, including the landmark ITER experiment. The results of these detailed experiments on plasma microturbulence will be shared with a variety of communities in the U.S. Results from the study of non-Brownian transport will be relevant to transport of turbulent heat and momentum and turbulent heating. In astrophysics, a better understanding of particle energization and heating will be achieved. Fusion energy research depends critically on a proper characterization of particle transport, since an effective machine must have a large energy density in the core. This characterization will be improved by the analysis of the data and simulations of TORPEX in this research.