Time response improvement for divertor heat flux monitoring in nuclear fusion devices

ITER is expected to be the first fusion device that produces net energy with fusion energy gain factor of more than 10. During unsteady stages in the operation, short time plasma heat load would be higher than that of the sun surface and finally exposes to the divertor plate. Thus, monitoring and controlling the heat load to plasma facing material are essential issues in plasma physics, material science, and heat transfer technology. The scope of this study is to deduce the time dependent heat flux from temperature evolution of plasma facing material target. To do that, constructed sensor must reproduce the real temperature evolution, and the corresponding estimation model must satisfy the heat conservation law. Recently, sensor designs have been upgraded to have a smaller effective size to reduce thermal diffusion time. However, a common delay coming from TC system with order of approximately hundreds ms is reported to involve in the thermocouple signal in several fusion devices in Japan such as Heliotron J (Kyoto University), GAMMA 10/PDX (University of Tsukuba), and LHD (National Institute for Fusion Science). To verify the estimation model and investigate the reason of time delay, we have conducted sensor test in neutral beam (short pulse) facility. Besides, commercial thermocouple delay tests were also carried out for the same purpose. Details would be presented on the conference site. (author)