892. JT-60粒子入射加熱装置(NBI)用クライオポンプ内気液二相ヘリウムの自然循環方式による流動特性

The cryopump for a JT-60 neutral beam injector (NBI) consists of six cryopanels cooled by liquid He below 3.7 K. To evacuate the H2 gas stably, it is necessary to supply liquid He to the six cryopanels sufficiently. Visual experiments were made with a glass model of the JT-60 NBI cryopump in order to confirm usefulness of the natural circulation for cooling the cryopanels. The two-phase He flow was observed to be homogenious flow, liquid and gas mixed uniformly, circulating smoothly through the cryopanels and pipes. The velocities of two-phase He through the channels were measured by means of the tracer introduced in the liquid He. A one-dimensional network calculation model of the cryopump was developed to calculate the flow distributions of the two-phase He into the cryopanels in the natural circulation. The model predicted well the velocities of the two-phase He in the glass model, and was used to predict the natural circulation flow characteristics in the JT-60 NBI cryopump. From the result of the sufficient supply of liquid He to the cryopanels, the natural circulation system was adopted for cooling the JT-60 NBI cryopanels.