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High-resolution millimeter-wave reflectometry for electron density profile measurements in tokamak plasmas

机译：用于托卡马克等离子体中电子密度分布测量的高分辨率毫米波反射仪

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摘要

A highly reliable density profile reflectometer system, which is relevant for current and future magnetic fusion research devices, has been developed on the DIII-D tokamak. Broadband frequency-modulated (EM) reflectometry has been selected as a benchmark system for this thesis research, while simultaneously assessing the relative merits of alternative techniques. Utilized broadband FM systems are a BWO-based reflectometer and a new solid-state fast-sweep reflectometer. A significant improvement in reflectometer profile measurements has been achieved through the advanced signal analysis utilizing digital complex demodulation (CDM) which improved phase accuracy (${le}pi/10).$ The CDM, which is a software implementation of heterodyne quadrature techniques, has been successfully applied for broadband FM reflectometry for the first time. In processing reflectometer profiles, important radar design parameters such as range resolution, precision and spatial sampling were optimized for reliable measurements. The reflectometer-measured profiles were generally in good agreement with other independently calibrated diagnostics such as Thomson scattering, Langmuir probe and multichannel interferometry. In low density discharges the reflectometer profiles reached almost to the machine center. The measured profiles were also used for physics studies such as the RF wave coupling with plasmas. While the BWO-based system with a moderate frequency sweep rate (400-600 $mu$s) produced reliable profiles with the improved analysis, the time resolution was limited due to tube reset-time ($sim$3 ms) and phase averaging to minimize density fluctuation effects. However, with development of the fast-sweep system, the rf frequency was swept fullband every 100 $mu$S without reset-time. Since fast frequency sweep significantly reduced turbulence effects on measurements, the system has produced very reliable individual profiles, which greatly enhanced the time resolution. The fast-sweep system has resolved fast-changing profiles across L-H transitions and dramatic edge density changes during ELMs with high temporal (${le}100mu$s) and spatial ($sim$1 cm) resolution, which is unprecedented using any other techniques. New information on the edge profile transition time in L-H transitions and ELMs has been obtained from the measurements. The thesis presents details of basic principles, analysis techniques, numerical simulations and implementation of the profile reflectometer system as well as the experimental results obtained in tokamak plasmas.
机译：在DIII-D托卡马克上已经开发了高度可靠的密度分布反射仪系统，该系统与当前和将来的磁聚变研究设备相关。宽带调频（EM）反射法已被选为本文研究的基准系统，同时评估了替代技术的相对优点。利用的宽带FM系统是基于BWO的反射仪和新的固态快速扫描反射仪。通过利用数字复合解调（CDM）进行的高级信号分析，可以提高反射仪的轮廓测量结果，从而改善了相位精度（$ {le} pi / 10）。CDM是外差正交技术的软件实现，首次成功应用于宽带FM反射仪。在处理反射仪轮廓时，对重要的雷达设计参数（例如距离分辨率，精度和空间采样）进行了优化，以实现可靠的测量。反射计测量的轮廓通常与其他独立校准的诊断程序（例如Thomson散射，Langmuir探头和多通道干涉仪）非常吻合。在低密度放电中，反射仪的轮廓几乎到达了机器中心。测得的轮廓还用于物理研究，例如与等离子体耦合的RF波。虽然基于BWO的系统具有中等频率扫描速率（400-600μs/μs），并通过改进的分析产生了可靠的曲线，但由于电子管复位时间（sim3μs）和相位平均到最小化密度波动的影响。但是，随着快速扫描系统的发展，射频频率每100μμS扫描全频带，而无需复位时间。由于快速扫频显着减少了湍流对测量的影响，因此该系统生成了非常可靠的单个轮廓，从而大大提高了时间分辨率。快速扫描系统已解决了在LM过渡期间快速变化的轮廓以及在ELM中具有高时间（$ {le} 100mu $ s）和空间（$ sim $ 1 cm）分辨率的急剧变化的边缘密度变化的情况，这是任何其他技术都无法做到的。从测量中获得了有关L-H过渡和ELM中边缘轮廓过渡时间的新信息。本文详细介绍了轮廓反射仪系统的基本原理，分析技术，数值模拟和实现，以及在托卡马克等离子体中获得的实验结果。

著录项

  • 作者

    Kim, Kang Wook.;

  • 作者单位

    University of California, Los Angeles.;

  • 授予单位 University of California, Los Angeles.;
  • 学科 Electrical engineering.;Plasma physics.
  • 学位 Ph.D.
  • 年度 1996
  • 页码 283 p.
  • 总页数 283
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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