UKAEA/CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom.
Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GL, United Kingdom.
Rev Sci Instrum. 2023 Jan 1;94(1):013506. doi: 10.1063/5.0128057.
Thomson scattered light is polarized in the same orientation as the incident laser beam at low electron temperatures (T). At high T, part of the spectrum begins to become randomly polarized due to relativistic reasons. First measurements of the depolarized Thomson scattering spectrum were obtained from Joint European Torus (JET) pulses in 2016. This paper builds upon these initial measurements with the data obtained during 2021. These new measurements improve upon first results, in particular, by obtaining spectral measurements of the depolarized spectrum. The recent JET campaign was well suited to these measurements with long and hot plasmas. The resulting data are averaged over many plasmas and laser pulses to obtain a measurement of the amount of "p" and "s" scattered light as a function of T. This experimentally obtained d(p/s)/dT is then fitted and found to show reasonable agreement with the theoretically predicted depolarized fraction. Error estimates on the measured "p/s" have been obtained and show that the measurements are meaningful. This is good news for ITER for which the intention is to use this measurement as a check on T determined by the core plasma Thomson scattering diagnostic by using conventional spectral measurement techniques.
在低电子温度（T）下，汤姆逊散射光的偏振方向与入射激光束相同。在高温下，由于相对论的原因，部分光谱开始变得随机偏振。2016 年，首次从联合欧洲托卡马克（JET）脉冲中获得了去极化汤姆逊散射光谱的测量结果。本文基于这些初始测量结果，结合 2021 年获得的数据进行了研究。这些新的测量结果改进了最初的结果，特别是通过获得了去极化光谱的光谱测量结果。最近的 JET 实验非常适合进行这些测量，因为实验获得了长时间的高温等离子体。最终的数据是通过对许多等离子体和激光脉冲进行平均得到的，以获得 T 随散射光“p”和“s”的散射光的测量值。然后对实验获得的 d(p/s)/dT 进行拟合，发现与理论预测的去极化部分具有很好的一致性。对测量的“p/s”进行了误差估计，并表明测量结果是有意义的。这对 ITER 来说是个好消息，因为其目的是使用这种测量方法作为对核心等离子体汤姆逊散射诊断确定的 T 的检查，该诊断方法使用传统的光谱测量技术。
