Fabrication of circling orbit in LHD vacuum vessel and confirmation work of its installation

National Institute for Fusion Science aims to generate the plasma with even higher performance using large helical device (LHD). For this purpose, reinforcement of heating equipment, renewal of basic equipment such as a vacuum exhaust system, and improvement of measuring equipment, etc. are promoted. Calibration with a calibration radiation source is required to increase the accuracy of instrument to evaluate the performance of plasma. This paper summarized the fabrication and installation confirmation operation of the circling orbit installed in the LHD vacuum vessel for instrument calibration. In the vacuum vessel, there is a restriction on the carried-in items to prevent contamination, and there is also a restriction on the size of parts that can be carried in due to the shape of inlet. There was another problem that needs to be cleared: for example, installation needed to be carried out in a limited time for maintenance work and prevention of interference. As for the circling orbit body, it was possible to reduce the production period and budget by the use of a railway model that has been proven by other devices. As for the circling moving body, this project enhanced the durability of the drive unit and stabilized the continuous operation. In preparation for actual calibration experiments, the installation procedure was changed since track installation tests revealed the necessity of installing fall prevention guides. In the future, this project plans to install a radiation source for simulated calibration onto the circling moving body and to conduct circling experiments. It is also necessary to examine the installation procedure in detail, to make workers understand the detail of work, and to prepare a circuit counting method. (A.O.)