Pandya Shwetang N, Peterson Byron J, Kobayashi Masahiro, Pandya Santosh P, Mukai Kiyofumi, Sano Ryuichi
High Temperature Plasma Physics Research Division, The Graduate University of Advanced Studies, 322-6 Oroshi-cho, Toki 509-5292, Japan.
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan.
Rev Sci Instrum. 2014 Dec;85(12):123501. doi: 10.1063/1.4902183.
The infrared imaging video bolometer (IRVB) used for measurement of the two-dimensional (2D) radiation profiles from the Large Helical Device has been significantly upgraded recently to improve its signal to noise ratio, sensitivity, and calibration, which ultimately provides quantitative measurements of the radiation from the plasma. The reliability of the quantified data needs to be established by various checks. The noise estimates also need to be revised and more realistic values need to be established. It is shown that the 2D heat diffusion equation can be used for estimating the power falling on the IRVB foil, even with a significant amount of spatial variation in the thermal diffusivity across the area of the platinum foil found experimentally during foil calibration. The equation for the noise equivalent power density (NEPD) is re-derived to include the errors in the measurement of the thermophysical and the optical properties of the IRVB foil. The theoretical value estimated using this newly derived equation matches closely, within 5.5%, with the mean experimental value. The change in the contribution of each error term of the NEPD equation with rising foil temperature is also studied and the blackbody term is found to dominate the other terms at elevated operating temperatures. The IRVB foil is also sensitive to the charge exchange (CX) neutrals escaping from the plasma. The CX neutral contribution is estimated to be marginally higher than the noise equivalent power (NEP) of the IRVB. It is also established that the radiation measured by the IRVB originates from the impurity line radiation from the plasma and not from the heated divertor tiles. The change in the power density due to noise reduction measures such as data smoothing and averaging is found to be comparable to the IRVB NEPD. The precautions that need to be considered during background subtraction are also discussed with experimental illustrations. Finally, the analysis algorithm with all the improvements is validated and found to reproduce the input power well within 10% accuracy. This article answers many fundamental questions relevant to the IRVB and illustrates the care to be exercised while processing the IRVB data.
用于测量大型螺旋装置二维辐射轮廓的红外成像视频测辐射热计（IRVB）最近进行了重大升级，以提高其信噪比、灵敏度和校准，最终实现对等离子体辐射的定量测量。量化数据的可靠性需要通过各种检查来确定。噪声估计也需要修订，并确定更符合实际的值。结果表明，即使在箔片校准过程中实验发现铂箔区域内热扩散率存在显著空间变化的情况下，二维热扩散方程仍可用于估算落在IRVB箔片上的功率。重新推导了噪声等效功率密度（NEPD）的方程，以纳入IRVB箔片热物理和光学性质测量中的误差。使用这个新推导的方程估计的理论值与平均实验值非常接近，误差在5.5%以内。还研究了NEPD方程各误差项的贡献随箔片温度升高的变化，发现黑体项在较高工作温度下占主导地位。IRVB箔片对从等离子体中逸出的电荷交换（CX）中性粒子也很敏感。CX中性粒子的贡献估计略高于IRVB的噪声等效功率（NEP）。还确定了IRVB测量的辐射源自等离子体的杂质线辐射，而非来自加热的偏滤器瓦块。发现诸如数据平滑和平均等降噪措施导致的功率密度变化与IRVB的NEPD相当。还通过实验示例讨论了背景扣除过程中需要考虑的注意事项。最后，对包含所有改进的分析算法进行了验证，发现其能在10%的精度范围内很好地再现输入功率。本文回答了许多与IRVB相关的基本问题，并说明了处理IRVB数据时需要注意的事项。
