Microwave interferometry has been used extensively for plasma diagnostics in tokamak for real-time electron density measurements. Real-time density measurement is an indispensable part of advanced tokamaks, as it can be used as feedback to control the plasma operation. In this article, we report the development of the phase extraction method in a heterodyne interferometer for real-time density estimation using a field-programmable gate array (FPGA). FPGA provides parallel processing, minimum control delay, more efficient processing architecture, and jitter-free synchronization between different control layers. Digital CORDIC algorithm is used for the estimation of the phase between two arms of the interferometer. A LabVIEW program is developed for the FPGA target and host controller to acquire the data and estimate electron density in real time, which can be used for feedback purpose by regulating the amount of gas injection using piezoelectric valve that requires a high voltage (~100 V) for about 1 ms. The delay in generating the feedback signal is proportional to the sampling speed (100 kHz) of the analog signal. In this work, line-averaged electron density measurement using digital signal processing (DSP) and LabVIEW-FPGA technology is presented. The developed interferometer and data acquisition (DAQ) system installed on ADITYA-U tokamak can measure the electron density in the range of 1 ×1018 - 1 ×1020 m-3. The algorithm used for the estimation of phase difference is validated using a conventional arctan method. The developed reconfigurable FPGA-based DAQ system uses low power, has a reconfigurable hardware structure for fast real-time signal processing, and can be easily upgraded.

中文翻译：

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基于 LabVIEW-FPGA 的 ADITYA-U 外差干涉测量实时数据采集系统


微波干涉测量法已广泛用于托卡马克等离子体诊断中的实时电子密度测量。实时密度测量是先进托卡马克不可或缺的一部分，因为它可以用作控制等离子体运行的反馈。在本文中，我们报告了使用现场可编程门阵列 (FPGA) 进行实时密度估计的外差干涉仪相位提取方法的开发。 FPGA提供并行处理、最小控制延迟、更高效的处理架构以及不同控制层之间的无抖动同步。数字 CORDIC 算法用于估计干涉仪两个臂之间的相位。为FPGA目标和主机控制器开发了一个LabVIEW程序，用于实时获取数据并估计电子密度，可以通过使用需要高电压（~100 V）的压电阀调节气体注入量来实现反馈目的）约1毫秒。生成反馈信号的延迟与模拟信号的采样速度 (100 kHz) 成正比。在这项工作中，提出了使用数字信号处理 (DSP) 和 LabVIEW-FPGA 技术进行线平均电子密度测量。所开发的干涉仪和数据采集（DAQ）系统安装在ADITYA-U托卡马克上，可以测量1×1018 - 1×1020 m-3范围内的电子密度。使用传统的反正切方法验证了用于估计相位差的算法。所开发的基于FPGA的可重构DAQ系统功耗低，具有可重构硬件结构，可实现快速实时信号处理，并且可以轻松升级。