Gourdain P-A, Peebles W A
Department of Physics and Astronomy, University of California Los Angeles, California 90095-1547, USA.
Rev Sci Instrum. 2008 Oct;79(10):10F102. doi: 10.1063/1.2969075.
Reflectometry has successfully demonstrated measurements of many important parameters in high temperature tokamak fusion plasmas. However, implementing such capabilities in a high-field, large plasma, such as ITER, will be a significant challenge. In ITER, the ratio of plasma size (meters) to the required reflectometry source wavelength (millimeters) is significantly larger than in existing fusion experiments. This suggests that the flow of the launched reflectometer millimeter-wave power can be realistically analyzed using three-dimensional ray tracing techniques. The analytical and numerical studies presented will highlight the fact that the group velocity (or power flow) of the launched microwaves is dependent on the direction of wave propagation relative to the internal magnetic field. It is shown that this dependence strongly modifies power flow near the cutoff layer in a manner that embeds the local magnetic field direction in the "footprint" of the power returned toward the launch antenna. It will be shown that this can potentially be utilized to locally determine the magnetic field pitch angle at the cutoff location. The resultant beam drift and distortion due to magnetic field and relativistic effects also have significant consequences on the design of reflectometry systems for large, high-field fusion experiments. These effects are discussed in the context of the upcoming ITER burning plasma experiment.
反射测量法已成功用于测量高温托卡马克聚变等离子体中的许多重要参数。然而，在像国际热核聚变实验堆（ITER）这样的高场大等离子体中实现这些功能将是一项重大挑战。在ITER中，等离子体尺寸（米）与所需反射测量源波长（毫米）的比值显著大于现有聚变实验中的比值。这表明可以使用三维射线追踪技术对发射的反射计毫米波功率流进行实际分析。所呈现的分析和数值研究将突出这样一个事实，即发射的微波的群速度（或功率流）取决于波传播方向相对于内部磁场的方向。结果表明，这种依赖性会以一种将局部磁场方向嵌入返回发射天线的功率“足迹”的方式，强烈改变截止层附近的功率流。还将表明，这有可能用于在截止位置局部确定磁场俯仰角。由于磁场和相对论效应导致的光束漂移和畸变，对大型高场聚变实验的反射测量系统设计也有重大影响。将在即将开展的ITER燃烧等离子体实验的背景下讨论这些效应。
