Studies of Laser-Aided Plasma Diagnostics on Fusion Machine

本研究的目的是将九州大学开发的激光辅助等离子体诊断方法应用于大尺寸的聚变等离子体装置，该装置由于存在大型加热系统，导流板和DT燃烧期间的中子屏蔽（最终用于超导磁体的低温恒温器）而具有有限的光学通道，并验证其实用性。为此目的，我们执行了三个研究方案。它们是：(1)以高空间和时间分辨率测量电子温度和密度，(2)研究测量电子密度波动的可能性，这被认为是导致磁场中异常快速的等离子体损失的原因，以及(3)研究测量被限制在磁场中的aloha粒子的密度和速度分布的可能性。研究的主要结果如下：对于项目(1)，JET之前引入了激光雷达汤姆逊散射来克服传统汤姆逊散射的缺点，传统汤姆逊散射需要两个大窗口来测量电子温度和密度。然而，激光雷达汤姆逊散射的空间分辨率，由光电倍增管的响应时间决定，超过120毫米有时是不够的。我们开发了一种利用条纹相机作为探测器的技术，提高了探测器的响应时间，从而将空间分辨率提高到50毫米。利用该装置，出现了精细的电子密度结构，特别是在等离子体边缘和颗粒燃料放电过程中，存在较大的密度梯度。为了改善这些测量的时间行为，需要一种新的激光器，我们提出了使用激光脉冲压缩方案来获得这样的激光器。对于项目(2)，我们研究了我们开发的用于测量电子密度波动的激光相位对比方法对JET等离子体的适用性，并发现这是可行的。同时，对反射仪测量中电子密度波动的局域化进行了理论研究，发现反射激光器的波动对信号的影响最为深刻。对于第(3)项，从理论上评估了速度分布对回旋管散射测量信号的影响，并在此基础上讨论了测量精度。此外，还同喷气加速器工作人员一起为计划从1993年下半年开始进行的主要DT实验准备回旋加速器实验。除了这些方案外，在这一合作过程中，我们认识到在分流区测量原子氢密度的重要性。为此，我们提出了我们在实验室开发的双光子激发激光诱导荧光，并进行了JET的设计研究。总结这些结果，我们获得了利用激光诊断聚变等离子体的非常有价值的信息，并显示了新的诊断潜力。这些发现将用于设计和执行下一代核聚变机器的测量，如ITER。少

the objective of this research is to apply the laser-aided plasma diagnostic methods developed Kyushu University, to a fusion plasma device with large dimension, which has a limited optical access due to the presence of large heating systems, divertor plates and neutron shielding during DT burning (and eventually a cryostat for superconducting magnets), and to verify their usefulness. We have performed three research programmes for this purpose. These are, (1) to measure electron temperature and density with high spatial and temporal resolutions, (2) to investigate a possibility of measuring electron density fluctuations, which have been believed to be responsible for an anomalously fast plasma losses across a magnetic field, and (3) to investigate a possibility of measuring density and velocity ditribution of aloha particles confined in a magnetic field. Main results of the study is as follows.For the item (1), JET had previously introduced a LIDAR Thomson scattering t overcome the sh … More ortcoming of the conventional Thomson scattering, which required two large windows, for measurements of electron temperature and density. However, the spatial resolution of the LIDAR Thomson scattering, decided by the responce time of a photomultiplier, of more than 120 mm was sometimes not sufficient. We have developed a technique to utilize a streak camera as a detector to improve the responce time of the detector, and consequently the spatial resolution was improved to 50 mm. Using this device, a fine structure of electron density has been emerged, especially at the plasma edge and during the pellet-fueled discharges, where a large density density gradient existed. In to order to improve the temporal behavior of these measurements, a new laser is required and we proposed t get such a laser using a laser pulse compression scheme.For the item (2), We studied an applicability of laser phase contrast method, which we have developed for measurements of electron density fluctuations, to JET plasmas, and found that this is feasible. Also, a theoretical study was carried out about the localization of electron density fluctuations on a reflectometer measurement, and it was found that fluctuations at the reflecting laser most profoundly affected the signal.And for the item (3), the effect of velocity distribution on the measured signal of gyrotron scattering was assessed theoretically, and the measurement accuracy was discussed based on the result. In addition, a preparation of the gyrotron experiment was made, together with the JET staff, for the main DT experiment planned from the latter half of the year 1993.In addition to these programmes, in the course of this collaboration, we have recognized the importance of measuring atomic hydrogen density at the divertor region. For this measurement, we proposed two-photon excited laser induced fluorescence, which we have developed at our laboratory, and design study for JET was performed.Summarizing these results, we gained a very valuable information of fusion plasmas using laser diagnostics, and showed potentials of new diagnostics. These findings will be used for the design and execution of measurements on the next generation of fusion machine, such as ITER. Less